diff --git a/src/passes/wasm/compile_package.rs b/src/passes/wasm/compile_package.rs
index cd62c6e..0e158a6 100644
--- a/src/passes/wasm/compile_package.rs
+++ b/src/passes/wasm/compile_package.rs
@@ -233,8 +233,7 @@ fn compile_one(
     })?;
   let marks = crate::passes::debug_marks::analyse(&lifted, &desugared);
   let fqn_prefix = format!("{canonical_url}:");
-  let mut frag = super::lower::lower(&lifted.result, &desugared.ast, &fqn_prefix);
-  frag.module_id = module_id;
+  let mut frag = super::lower::lower(&lifted.result, &desugared.ast, &fqn_prefix, module_id);
   // module_imports stays as raw-URL → ModuleId. The package compiler
   // resolves URLs at the call site; the lower pass populates this
   // field by walking `cps.module_imports` keys and mapping each raw
@@ -340,6 +339,7 @@ pub const MIGRATED_STDLIB_FNK: &[&str] = &[
   "std/testing.fnk",
   "std/io.fnk",
   "std/iter.fnk",
+  "std/trace.fnk",
 ];
 
 #[cfg(feature = "compile")]
diff --git a/src/passes/wasm/emit.rs b/src/passes/wasm/emit.rs
index d9a16d9..c5a0766 100644
--- a/src/passes/wasm/emit.rs
+++ b/src/passes/wasm/emit.rs
@@ -53,6 +53,31 @@ use wasm_encoder::{
 use super::ir::*;
 use super::runtime_contract::import_key;
 
+// ── linear-memory map ────────────────────────────────────────────
+//
+// emit is the single owner of linear-memory byte layout. The linker
+// remaps symbol *indices* (which global, which data segment); the
+// *byte offsets* of everything in linear memory are assigned here.
+//
+// Layout of the single memory page (64 KiB):
+//
+//   [0, TRACE_BYTES)            trace activation-stack region (reserved)
+//   [TRACE_BYTES, SCRATCH_BASE) literal data pool (grows up at compile time)
+//   [SCRATCH_BASE, 64 KiB)      host-IO scratch window
+//
+// SCRATCH_BASE is the host-exchange window the JS interop bounces
+// bytes through. It is declared in the runtime WAT today; this constant
+// is the layout authority's copy used to bound the data pool.
+
+/// Trace activation-stack region at the bottom of memory. Must match
+/// rt/trace.wat's window: TRACE_CAP (64) frames x FRAME_BYTES (16, four
+/// i32s `{fn_mid, fn_cid, call_mid, call_cid}`) = 1024 bytes.
+const RING_BYTES: u32 = 64 * 16;
+
+/// Host-IO scratch window base. Must match the runtime WAT's
+/// `SCRATCH_BASE` global (`interop/js/interop.wat`).
+const SCRATCH_BASE: u32 = 0xC000;
+
 /// Output of `emit::emit`. The binary plus a per-InstrId map of absolute
 /// byte offsets in the binary. Only InstrIds that were tagged with a
 /// `cps_id` in lower (and thus need to participate in mark finalisation)
@@ -160,6 +185,7 @@ fn linked_runtime(interop: Interop) -> &'static LinkedRuntime {
     let modules: &[(&str, &str)] = &[
       ("interop.wat",      interop_src),
       ("rt/apply.wat",     include_str!("../../runtime/rt/apply.wat")),
+      ("rt/trace.wat",     include_str!("../../runtime/rt/trace.wat")),
       ("rt/opaque.wat",    include_str!("../../runtime/rt/opaque.wat")),
       ("rt/modules.wat",   include_str!("../../runtime/rt/modules.wat")),
       ("rt/protocols.wat", include_str!("../../runtime/rt/protocols.wat")),
@@ -713,15 +739,26 @@ pub fn emit_with_offsets(frag: &Fragment, interop: Interop) -> EmitOutput {
   };
 
   // Data: lay out user fragment's `frag.data` blobs sequentially in
-  // memory starting at offset 0. Each `DataSym(i)` resolves to the
-  // running offset, used by `Operand::DataRef` at emit time.
+  // memory starting at `RING_BYTES` (the bottom region is reserved for
+  // the trace ring). Each `DataSym(i)` resolves to its absolute byte
+  // offset, used by `Operand::DataRef` at emit time.
   let mut data_offsets: Vec<u32> = Vec::with_capacity(frag.data.len());
   let mut data_blob: Vec<u8> = Vec::new();
   for d in &frag.data {
-    data_offsets.push(data_blob.len() as u32);
+    data_offsets.push(RING_BYTES + data_blob.len() as u32);
     data_blob.extend_from_slice(&d.bytes);
   }
 
+  // The data pool must not grow into the host-IO scratch window. Data
+  // size is fully known here, so this is a hard compile-time invariant.
+  let data_top = RING_BYTES + data_blob.len() as u32;
+  assert!(
+    data_top <= SCRATCH_BASE,
+    "literal data pool ({} bytes ending at {data_top:#x}) overflows into \
+     the host-IO scratch window at {SCRATCH_BASE:#x}",
+    data_blob.len(),
+  );
+
   // Code: runtime's bodies raw, then user's bodies encoded.
   let mut code_sec = CodeSection::new();
   for body in &rt.code_bodies_raw {
@@ -738,16 +775,16 @@ pub fn emit_with_offsets(frag: &Fragment, interop: Interop) -> EmitOutput {
     user_body_offsets.push((final_idx, body_offsets));
   }
 
-  // Data section: one active segment at offset 0 in memory 0 holding
-  // the concatenated blobs. Skip if there's no data.
+  // Data section: one active segment at `RING_BYTES` in memory 0
+  // holding the concatenated blobs. Skip if there's no data.
   let data_sec = if data_blob.is_empty() {
     None
   } else {
     let mut sec = wasm_encoder::DataSection::new();
     sec.active(
-      0,                                 // memory index
-      &ConstExpr::i32_const(0),          // offset
-      data_blob.iter().copied(),         // bytes
+      0,                                       // memory index
+      &ConstExpr::i32_const(RING_BYTES as i32), // offset
+      data_blob.iter().copied(),               // bytes
     );
     Some(sec)
   };
@@ -1186,6 +1223,54 @@ mod tests {
     assert!(!lr.bytes.is_empty(), "JS runtime should link to non-empty bytes");
   }
 
+  /// The linear-memory map reserves a RING region at the bottom of
+  /// memory; the literal data pool must start at `RING_BYTES`, not at
+  /// offset 0. Asserted via the emitted data section's active-segment
+  /// offset.
+  #[test]
+  fn data_pool_starts_above_ring_region() {
+    let mut frag = Fragment::default();
+    frag.data.push(DataDecl { bytes: b"hi".to_vec(), display: None });
+
+    let bytes = emit(&frag, Interop::Js);
+
+    let mut seg_offset: Option<u64> = None;
+    let parser = wasmparser::Parser::new(0);
+    for payload in parser.parse_all(&bytes) {
+      if let Ok(wasmparser::Payload::DataSection(reader)) = payload {
+        for data in reader.into_iter().flatten() {
+          if let wasmparser::DataKind::Active { offset_expr, .. } = data.kind {
+            let mut ops = offset_expr.get_operators_reader();
+            if let Ok(wasmparser::Operator::I32Const { value }) = ops.read() {
+              seg_offset = Some(value as u32 as u64);
+            }
+          }
+        }
+      }
+    }
+
+    assert_eq!(
+      seg_offset,
+      Some(RING_BYTES as u64),
+      "data active segment should start at RING_BYTES ({RING_BYTES}), \
+       leaving [0, RING_BYTES) reserved for the trace ring"
+    );
+  }
+
+  /// The data pool growing into the scratch window is a hard compile-
+  /// time error, not silent corruption.
+  #[test]
+  #[should_panic(expected = "overflows into the host-IO scratch window")]
+  fn data_pool_overflowing_scratch_window_panics() {
+    let mut frag = Fragment::default();
+    // One blob large enough that RING_BYTES + len exceeds SCRATCH_BASE.
+    frag.data.push(DataDecl {
+      bytes: vec![0u8; SCRATCH_BASE as usize],
+      display: None,
+    });
+    emit(&frag, Interop::Js);
+  }
+
   #[test]
   fn js_runtime_exports_i31_helpers() {
     let lr = linked_runtime(Interop::Js);
diff --git a/src/passes/wasm/lower.rs b/src/passes/wasm/lower.rs
index 05215e7..172e183 100644
--- a/src/passes/wasm/lower.rs
+++ b/src/passes/wasm/lower.rs
@@ -50,6 +50,29 @@ fn origin_of(cps: &CpsResult, ast: &Ast<'_>, id: CpsId) -> Option<ByteRange> {
   Some(ByteRange::new(loc.start.idx, loc.end.idx))
 }
 
+/// True iff this CpsId's source origin is an `Apply` AST node — i.e. a
+/// call the user actually wrote, not a desugar-synthesised apply (pipe
+/// expansion, partial application, etc.) whose origin is the surrounding
+/// `InfixOp`/`Pipe`/lambda node. Used to gate trace instrumentation so
+/// the trace reflects source-level calls.
+fn is_source_apply(cps: &CpsResult, ast: &Ast<'_>, id: CpsId) -> bool {
+  let Some(Some(ast_id)) = cps.origin.try_get(id) else { return false };
+  matches!(ast.nodes.get(*ast_id).kind, crate::ast::NodeKind::Apply { .. })
+}
+
+/// True iff this CpsId's source origin is a `Fn` AST node — i.e. a
+/// function the user actually wrote, not a desugar-synthesised
+/// `CpsFunction` (e.g. the `m_0`/`mp_N` match-block wrappers, whose
+/// origin is the surrounding `Match` node). Used to gate trace-frame
+/// pushes so the activation stack reflects only source-level functions;
+/// synth `CpsFunction`s route through the no-push/inherit path like a
+/// `CpsClosure`, keeping push/pop balanced and the trace free of `:0`
+/// synth frames.
+fn is_source_fn(cps: &CpsResult, ast: &Ast<'_>, id: CpsId) -> bool {
+  let Some(Some(ast_id)) = cps.origin.try_get(id) else { return false };
+  matches!(ast.nodes.get(*ast_id).kind, crate::ast::NodeKind::Fn { .. })
+}
+
 /// Lower a lifted CPS result to an unlinked wasm IR `Fragment`.
 ///
 /// `fqn_prefix` is the module's fully-qualified URL prefix (e.g.
@@ -62,7 +85,7 @@ fn origin_of(cps: &CpsResult, ast: &Ast<'_>, id: CpsId) -> Option<ByteRange> {
 /// Phase-4A: prefix is purely a cosmetic / naming concern. The entry
 /// function's export name still stays `"fink_module"`; rewiring the
 /// body to the `import_module` init-guard shape lands in 4D.
-pub fn lower(cps: &CpsResult, ast: &Ast<'_>, fqn_prefix: &str) -> Fragment {
+pub fn lower(cps: &CpsResult, ast: &Ast<'_>, fqn_prefix: &str, module_id: ModuleId) -> Fragment {
   let mut usage = runtime_contract::scan(cps);
   // Fn3 / ctx-aware lowering routes user-fn calls through `apply_3`
   // instead of `apply`. Mark the Apply3 runtime symbol so `declare()`
@@ -70,6 +93,15 @@ pub fn lower(cps: &CpsResult, ast: &Ast<'_>, fqn_prefix: &str) -> Fragment {
   // harmless here; lower_ctx never emits a call to it.
   usage.mark(runtime_contract::Sym::Apply3);
   usage.mark(runtime_contract::Sym::Fn3);
+  // Trace instrumentation (rt/trace.wat): each userland fn body pushes a
+  // frame on entry and pops on return; each userland call site marks the
+  // current frame's call site.
+  usage.mark(runtime_contract::Sym::TracePush);
+  usage.mark(runtime_contract::Sym::TraceMark);
+  usage.mark(runtime_contract::Sym::TracePop);
+  // Each fink_module self-registers its (module_id, url) so trace frames
+  // resolve to a source url (rt/modules.wat).
+  usage.mark(runtime_contract::Sym::RegisterModule);
   // Per-module wrapper synthesised below uses init_module and the
   // closure/captures/str primitives.
   usage.mark(runtime_contract::Sym::ModulesInitModule);
@@ -77,7 +109,11 @@ pub fn lower(cps: &CpsResult, ast: &Ast<'_>, fqn_prefix: &str) -> Fragment {
   usage.mark(runtime_contract::Sym::Captures);
   usage.mark(runtime_contract::Sym::Cell);
   usage.mark(runtime_contract::Sym::StrFromData);
-  let mut frag = Fragment::default();
+  // module_id set here (not after lowering): trace_push / register_module
+  // bake the module id as a constant at emit time, so it must be correct
+  // during lowering. (compile_package used to set frag.module_id after
+  // lower returned, which was too late for those emitted constants.)
+  let mut frag = Fragment { module_id, ..Default::default() };
   let rt = runtime_contract::declare(&mut frag, &usage);
 
   // CPS root shape: App(FinkModule, [Cont::Expr { args: [ƒctx, ƒret], body }]).
@@ -172,7 +208,7 @@ pub fn lower(cps: &CpsResult, ast: &Ast<'_>, fqn_prefix: &str) -> Fragment {
     // CpsId. We walk the chain pre-order: outer LetFn first.
     let mut top_fn_syms: HashMap<CpsId, FuncSym> = HashMap::new();
     let mut node = &lcx.cps.root;
-    while let ExprKind::LetFn { name, params, fn_body, cont, .. } = &node.kind {
+    while let ExprKind::LetFn { name, params, fn_body, cont, fn_kind, .. } = &node.kind {
       let mut cap_ids: Vec<CpsId> = Vec::new();
       let mut user_ids: Vec<(CpsId, bool)> = Vec::new();
       for p in params {
@@ -188,10 +224,17 @@ pub fn lower(cps: &CpsResult, ast: &Ast<'_>, fqn_prefix: &str) -> Fragment {
       }
       let raw_display = cps_ident_for_bind(lcx.cps, lcx.ast, name);
       let display = format!("{}{}", lcx.fqn_prefix, raw_display);
+      use crate::passes::cps::ir::CpsFnKind;
+      let trace = match fn_kind {
+        CpsFnKind::CpsFunction if is_source_fn(lcx.cps, lcx.ast, name.id) =>
+          TraceFrame::entry(name.id),
+        _ => TraceFrame::cont(None),  // synth/closure: no frame, no enclosing
+      };
       let fn_sym = lower_fn(
         &mut lcx,
         &cap_ids, &user_ids, fn_body, &display,
         &top_fn_syms,
+        trace,
       );
       top_fn_syms.insert(name.id, fn_sym);
       node = match cont {
@@ -207,6 +250,7 @@ pub fn lower(cps: &CpsResult, ast: &Ast<'_>, fqn_prefix: &str) -> Fragment {
       module_body,
       &module_display,
       &top_fn_syms,
+      TraceFrame::cont(None),  // module body is synth: no frame, no enclosing
     );
     let FuncSym::Local(_) = fink_module else { panic!("lower: fink_module must be Local"); };
     // No WASM-level export for fink_module — host accesses the module
@@ -214,6 +258,10 @@ pub fn lower(cps: &CpsResult, ast: &Ast<'_>, fqn_prefix: &str) -> Fragment {
     // canonical FQN. fink_module stays as a bare internal func; the
     // wrapper holds a no-capture closure over it.
 
+    // Self-register (module_id, url) at the top of fink_module so trace
+    // frames (which carry module_id) can resolve back to a source url.
+    prepend_module_registration(&mut lcx, fink_module);
+
     // Per-module host-facing wrapper. Exported under the module's
     // canonical FQN so the host can call any module by URL string
     // (`instance.get_func(canonical_url)`). The wrapper composes the
@@ -250,6 +298,47 @@ pub fn lower(cps: &CpsResult, ast: &Ast<'_>, fqn_prefix: &str) -> Fragment {
 /// synthesises a placeholder ctx (ref.i31 42) and tail-calls the
 /// body's Fn3 entry. Once the substrate lands, host-provided ctx
 /// flows in through the same channel.
+/// Prepend a `register_module(module_id, url)` call to the top of the
+/// module's `fink_module` body. `module_id` is the fragment's own id (a
+/// compile-time constant); `url` is the canonical url materialised as a
+/// `$Str`. This is how the runtime learns module_id → url for resolving
+/// trace frames.
+fn prepend_module_registration(lcx: &mut LowerCtx<'_>, fink_module: FuncSym) {
+  let FuncSym::Local(fi) = fink_module else {
+    panic!("prepend_module_registration: fink_module must be Local");
+  };
+  let fi = fi as usize;
+
+  let canonical_url = lcx.fqn_prefix.trim_end_matches(':').to_string();
+  let mid = lit_i32(lcx.frag.module_id.0 as i32);
+
+  // Allocate a fresh local on fink_module for the url $Str. New locals
+  // index after params + existing locals.
+  let url_idx = LocalIdx(
+    (lcx.frag.funcs[fi].params.len() + lcx.frag.funcs[fi].locals.len()) as u32,
+  );
+  lcx.frag.funcs[fi].locals.push(LocalDecl {
+    ty: val_anyref(true),
+    display: Some(":mod_reg_url".to_string()),
+  });
+
+  // url = from_data(intern(canonical_url)) — same materialisation the
+  // host wrapper uses for the registry key.
+  let sym = intern_data(lcx.frag, canonical_url.as_bytes());
+  let len = canonical_url.len() as u32;
+  let i_url = push_call(lcx.frag, lcx.rt.str_from_data(),
+    vec![Operand::DataRef { sym, len }], Some(url_idx));
+
+  // register_module(mid, url)
+  let i_reg = push_call(lcx.frag, lcx.rt.register_module(),
+    vec![mid, op_local(url_idx)], None);
+
+  // Prepend both, url-const first, before the existing body.
+  let body = &mut lcx.frag.funcs[fi].body;
+  body.insert(0, i_reg);
+  body.insert(0, i_url);
+}
+
 fn synth_host_wrapper(
   lcx: &mut LowerCtx<'_>,
   fink_module: FuncSym,
@@ -367,6 +456,24 @@ struct LowerCtx<'a> {
 
 /// Lower a CPS function — either the module body or a LetFn'd helper.
 ///
+/// Trace identity for a lowered function. `entry = Some(id)` means this
+/// is a real userland function entry: push a frame for `id` at the
+/// prologue and pops inside it target `id`. `entry = None` means a lifted
+/// continuation (CpsClosure) - no push; its ret-cont pops target the
+/// *enclosing* userland fn in `enclosing`.
+#[derive(Clone, Copy, Default)]
+struct TraceFrame {
+  entry: Option<CpsId>,
+  enclosing: Option<CpsId>,
+}
+
+impl TraceFrame {
+  /// A real userland function entry, traced under its own id.
+  fn entry(id: CpsId) -> Self { Self { entry: Some(id), enclosing: None } }
+  /// A lifted continuation: no frame; ret-cont pops target `enclosing`.
+  fn cont(enclosing: Option<CpsId>) -> Self { Self { entry: None, enclosing } }
+}
+
 /// `cap_params` and `user_params` are the CpsIds of the function's
 /// cap-params (read from `$_caps` via `array.get`) and user-params
 /// (unpacked from `$_args` via successive `args_head`/`args_tail`).
@@ -379,6 +486,7 @@ fn lower_fn(
   body: &Expr,
   display: &str,
   fn_syms: &HashMap<CpsId, FuncSym>,
+  trace: TraceFrame,
 ) -> FuncSym {
   // CRITICAL: `fn_syms` is cloned (not shared) into the child FnCtx.
   // Sibling and ancestor LetFn FuncSyms must be visible to this fn's
@@ -449,6 +557,20 @@ fn lower_fn(
     }
   }
 
+  // Trace: a real userland function entry pushes an activation frame
+  // stamped with its own identity; pops inside it (when it invokes its
+  // return cont) target that frame. A lifted continuation (CpsClosure)
+  // does NOT push - it is part of the enclosing function - but its
+  // ret-cont invocations must pop the enclosing function's frame, so it
+  // inherits the enclosing fn's id for pop targeting.
+  ctx.trace_fn_id = trace.entry.or(trace.enclosing);
+  if let Some(fn_id) = trace.entry {
+    let mid = lit_i32(lcx.frag.module_id.0 as i32);
+    let cid = lit_i32(fn_id.0 as i32);
+    let i = push_call(lcx.frag, lcx.rt.trace_push(), vec![mid, cid], None);
+    ctx.instrs.push(i);
+  }
+
   // Walk the body.
   lower_expr(lcx, &mut ctx, body);
 
@@ -493,6 +615,12 @@ struct FnCtx {
   /// every "fresh" ctx CpsId at thread_ctx time aliases to the same
   /// wasm value at runtime.
   ctx_local: Option<LocalIdx>,
+  /// This function's own identity for trace instrumentation: the
+  /// defining LetFn's CpsId. `Some` for userland source functions (which
+  /// push/pop an activation frame); `None` for synth/runtime functions
+  /// (module body, host wrapper) which are not traced. Read by the
+  /// ret-cont arm to emit `trace_pop(module_id, fn_id)`.
+  trace_fn_id: Option<CpsId>,
 }
 
 impl FnCtx {
@@ -505,6 +633,7 @@ impl FnCtx {
       next_local_idx: 0,
       fn_syms,
       ctx_local: None,
+      trace_fn_id: None,
     }
   }
 
@@ -662,7 +791,7 @@ fn lower_expr(
       lower_cont(lcx, ctx, cont);
     }
 
-    ExprKind::LetFn { name, params, fn_body, cont, .. } => {
+    ExprKind::LetFn { name, params, fn_body, cont, fn_kind, .. } => {
       // Collect cap + user params by role. The `Bind::Caps` param is
       // the ƒcaps record (post closure-conversion); everything else is
       // a user param. User params carry their spread flag so the
@@ -685,10 +814,22 @@ fn lower_expr(
       // module's FQN prefix so cross-fragment merges stay collision-free.
       let raw_display = cps_ident_for_bind(lcx.cps, lcx.ast, name);
       let display = format!("{}{}", lcx.fqn_prefix, raw_display);
+      // A source-level CpsFunction is a real userland fn (push its own
+      // frame); a CpsClosure is a lifted continuation (no push; its
+      // ret-cont pops the enclosing fn, inherited via ctx.trace_fn_id).
+      // Synth CpsFunctions (e.g. the m_0/mp_N match-block wrappers)
+      // inherit too — they are not source-level activations.
+      use crate::passes::cps::ir::CpsFnKind;
+      let trace = match fn_kind {
+        CpsFnKind::CpsFunction if is_source_fn(lcx.cps, lcx.ast, name.id) =>
+          TraceFrame::entry(name.id),
+        _ => TraceFrame::cont(ctx.trace_fn_id),
+      };
       let fn_sym = lower_fn(
         lcx,
         &cap_ids, &user_ids, fn_body, &display,
         &ctx.fn_syms,
+        trace,
       );
       // The LetFn binds `name.id` to a funcref-valued local; we model
       // it as an anyref local holding a `ref.func` funcref. Actual
@@ -1041,6 +1182,20 @@ fn lower_expr(
         }
       };
 
+      // Trace pop: invoking this fn's return cont is the fn returning -
+      // pop its activation frame. Only for userland fns (trace_fn_id Some)
+      // and only when the cont being applied is this fn's Ret-kind cont.
+      if let Some(fn_id) = ctx.trace_fn_id
+        && matches!(
+          lcx.bind_kinds.try_get(cont_id).and_then(|b| *b),
+          Some(Bind::Cont(crate::passes::cps::ir::ContKind::Ret)))
+      {
+        let mid = lit_i32(lcx.frag.module_id.0 as i32);
+        let cid = lit_i32(fn_id.0 as i32);
+        let i = push_call(lcx.frag, lcx.rt.trace_pop(), vec![mid, cid], None);
+        ctx.instrs.push(i);
+      }
+
       let (ctx_op, rest_args) = split_ctx_arg(lcx, ctx, args);
       let l_args_list = build_args_list(lcx, ctx, rest_args);
       let i_app = push_return_call(lcx.frag, lcx.rt.apply_3(),
@@ -1069,6 +1224,7 @@ fn lower_expr(
 
       let (ctx_op, rest_args) = split_ctx_arg(lcx, ctx, args);
       let l_args_list = build_args_list(lcx, ctx, rest_args);
+      mark_call_site(lcx, ctx, expr.id);
       let i_app = push_return_call(lcx.frag, lcx.rt.apply_3(),
         vec![op_local(l_args_list), ctx_op, op_local(callee)]);
       set_cps_id(lcx.frag, i_app, expr.id);
@@ -1328,6 +1484,25 @@ fn unbox_anyref(
 /// `done`) or a Cont::Expr (lifted into a closure — not handled here
 /// since the lifting pass already produces that as App(FnClosure)
 /// ahead of the tail call).
+/// Emit `trace_mark(module_id, cps_id)` recording this call site into the
+/// current (top) activation frame, immediately before the user-fn dispatch.
+/// `cps_id` is the Apply node's id (the call site); `module_id` is the
+/// fragment's own id. Updates "where in the current function we are".
+///
+/// Only userland calls are marked: an Apply is marked iff it has a source
+/// origin. Desugar-synthesised applies (pipe expansion, partial
+/// application, etc.) have no origin and are skipped, so the trace
+/// reflects source-level calls, not the finer post-desugar CPS structure.
+fn mark_call_site(lcx: &mut LowerCtx<'_>, ctx: &mut FnCtx, call_site: CpsId) {
+  if !is_source_apply(lcx.cps, lcx.ast, call_site) {
+    return;
+  }
+  let module_id = lit_i32(lcx.frag.module_id.0 as i32);
+  let cps_id = lit_i32(call_site.0 as i32);
+  let i = push_call(lcx.frag, lcx.rt.trace_mark(), vec![module_id, cps_id], None);
+  ctx.instrs.push(i);
+}
+
 /// Build the `apply_3` args list from a heterogeneous arg sequence.
 ///
 /// Two-phase to keep the locals/instr order stable across changes:
diff --git a/src/passes/wasm/mod.rs b/src/passes/wasm/mod.rs
index db91801..cf18d15 100644
--- a/src/passes/wasm/mod.rs
+++ b/src/passes/wasm/mod.rs
@@ -204,7 +204,7 @@ mod tests {
     // Generic synthetic FQN — every fragment in the IR must have a
     // non-empty fqn_prefix; tests use `test:` so emitted exports
     // (per-module wrapper, etc.) are addressable by a stable name.
-    let user_frag = super::lower::lower(&lifted.result, &desugared.ast, "test:");
+    let user_frag = super::lower::lower(&lifted.result, &desugared.ast, "test:", crate::passes::wasm::ir::ModuleId(0));
     // Single-module programs today: the link step is a passthrough,
     // but routing through it keeps the tracer test surface honest
     // when multi-fragment merge arrives.
@@ -292,7 +292,7 @@ mod tests {
   #[cfg(test)]
   fn emit_for(src: &str) -> Vec<u8> {
     let (lifted, desugared) = crate::to_lifted(src, "test").unwrap_or_else(|e| panic!("{e}"));
-    let user_frag = super::lower::lower(&lifted.result, &desugared.ast, "test:");
+    let user_frag = super::lower::lower(&lifted.result, &desugared.ast, "test:", crate::passes::wasm::ir::ModuleId(0));
     let linked = super::link::link(&[user_frag]);
     super::emit::emit(&linked, super::emit::Interop::Rust)
   }
@@ -306,6 +306,35 @@ mod tests {
   /// helpers (args_empty + args_prepend) to construct. That full
   /// execution handshake is exercised by emit_executes_42 below.
   #[cfg(feature = "run")]
+  /// A user-function call site emits a `trace_push` recording the
+  /// call-site `(module_id, cps_id)` into the trace buffer, before the
+  /// `apply_3` dispatch. Builtin/runtime calls do NOT push.
+  #[test]
+  fn user_call_emits_trace_push() {
+    let out = wat("\
+add = fn a, b:
+  a + b
+add 3, 4
+");
+    assert!(
+      out.contains("rt/trace.wat:trace_push"),
+      "user-fn call should emit a trace_push at the call site; got:\n{out}"
+    );
+  }
+
+  /// Every module's `fink_module` self-registers its `(module_id, url)`
+  /// so `get_module_url` can resolve a trace frame's module id back to a
+  /// source url. The id is a compile-time constant; the url is the
+  /// module's canonical url string.
+  #[test]
+  fn fink_module_registers_its_url() {
+    let out = wat("42");
+    assert!(
+      out.contains("rt/modules.wat:register_module"),
+      "fink_module should call register_module(mod_id, url); got:\n{out}"
+    );
+  }
+
   #[test]
   fn emit_instantiates_in_wasmtime() {
     use wasmtime::{Config, Engine, Module, Store, Linker, Error, ExternType};
diff --git a/src/passes/wasm/runtime_contract.rs b/src/passes/wasm/runtime_contract.rs
index 0088a4a..52839f3 100644
--- a/src/passes/wasm/runtime_contract.rs
+++ b/src/passes/wasm/runtime_contract.rs
@@ -99,6 +99,18 @@ pub enum Sym {
   // 2c-B; until then, references are emitted as imports that will
   // remain unresolved (Phase A is shape-only, not runnable).
   Apply3,
+  // The trace primitives maintain a bounded activation stack in linear
+  // memory (rt/trace.wat). All `(i32, i32) -> ()`.
+  //   TracePush(fn_mid, fn_cid)   -- enter a userland fn body.
+  //   TraceMark(call_mid, call_cid) -- a call site within the current fn.
+  //   TracePop(fn_mid, fn_cid)    -- leave a userland fn body.
+  TracePush,
+  TraceMark,
+  TracePop,
+  // RegisterModule records module_id → url so trace frames can resolve
+  // to a source url. Signature `(i32, anyref) -> ()`. Each fink_module
+  // self-registers. Defined in rt/modules.wat.
+  RegisterModule,
 
   // ── polymorphic protocol operators (rt/protocols.wat) ─────────
   // All binary operators share the shape (anyref, anyref, anyref)
@@ -333,6 +345,10 @@ pub struct Runtime {
   args_concat:  Option<FuncSym>,
   apply:        Option<FuncSym>,
   apply_3:      Option<FuncSym>,
+  trace_push:   Option<FuncSym>,
+  trace_mark:   Option<FuncSym>,
+  trace_pop:    Option<FuncSym>,
+  register_module: Option<FuncSym>,
   // polymorphic protocol operators
   op_plus:    Option<FuncSym>,
   op_minus:   Option<FuncSym>,
@@ -427,6 +443,10 @@ impl Runtime {
   pub fn str_match(&self)    -> FuncSym { self.str_match.expect("rt: str_match not declared") }
   pub fn apply(&self)        -> FuncSym { self.apply.expect("rt: _apply not declared") }
   pub fn apply_3(&self)      -> FuncSym { self.apply_3.expect("rt: apply_3 not declared") }
+  pub fn trace_push(&self)   -> FuncSym { self.trace_push.expect("rt: trace_push not declared") }
+  pub fn trace_mark(&self)   -> FuncSym { self.trace_mark.expect("rt: trace_mark not declared") }
+  pub fn trace_pop(&self)    -> FuncSym { self.trace_pop.expect("rt: trace_pop not declared") }
+  pub fn register_module(&self) -> FuncSym { self.register_module.expect("rt: register_module not declared") }
   pub fn fn3(&self)          -> TypeSym { self.fn3.expect("rt: Fn3 not declared") }
 
   /// Look up the runtime func for a protocol operator `Sym`. Panics
@@ -511,6 +531,10 @@ pub(super) fn import_key(sym: Sym) -> &'static str {
     Sym::VarArgs         => "rt/apply.wat:VarArgs",
     Sym::Apply           => "rt/apply.wat:apply",
     Sym::Apply3          => "rt/apply.wat:apply_3",
+    Sym::TracePush       => "rt/trace.wat:trace_push",
+    Sym::TraceMark       => "rt/trace.wat:trace_mark",
+    Sym::TracePop        => "rt/trace.wat:trace_pop",
+    Sym::RegisterModule  => "rt/modules.wat:register_module",
 
     Sym::ArgsHead        => "rt/apply.wat:args_head",
     Sym::ArgsTail        => "rt/apply.wat:args_tail",
@@ -663,6 +687,10 @@ pub fn declare(frag: &mut Fragment, usage: &RuntimeUsage) -> Runtime {
   if needed.contains(&Sym::ArgsConcat)  { rt.args_concat  = Some(FuncSym::Runtime(Sym::ArgsConcat)); }
   if needed.contains(&Sym::Apply)       { rt.apply        = Some(FuncSym::Runtime(Sym::Apply)); }
   if needed.contains(&Sym::Apply3)      { rt.apply_3      = Some(FuncSym::Runtime(Sym::Apply3)); }
+  if needed.contains(&Sym::TracePush)   { rt.trace_push   = Some(FuncSym::Runtime(Sym::TracePush)); }
+  if needed.contains(&Sym::TraceMark)   { rt.trace_mark   = Some(FuncSym::Runtime(Sym::TraceMark)); }
+  if needed.contains(&Sym::TracePop)    { rt.trace_pop    = Some(FuncSym::Runtime(Sym::TracePop)); }
+  if needed.contains(&Sym::RegisterModule) { rt.register_module = Some(FuncSym::Runtime(Sym::RegisterModule)); }
 
   for sym in BINARY_OPS {
     if needed.contains(sym) {
diff --git a/src/passes/wasm/test_bindings.fnk b/src/passes/wasm/test_bindings.fnk
index 603523a..db6d827 100644
--- a/src/passes/wasm/test_bindings.fnk
+++ b/src/passes/wasm/test_bindings.fnk
@@ -19,6 +19,9 @@ test 'single binding export', fn:
         (local $:pub_name (ref null any))
         (local $:unwrap_foo_0 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_1 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_foo_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:foo (local.get $:cell_foo_0))
@@ -46,7 +49,7 @@ test 'single binding export', fn:
       (data $d_0 "test")
       (data $d_1 "foo")
     )
-    ;; sm:EbQIAJgBAJgBAGgBAAOGAQCgAQCqAQCUAQCWAQDKAQCwAQBuAM4BAKYFAHoA5gEAjAEA
+    ;; sm:E4YJAJwBAKYBAJgBAJgBAGgBAAOGAQCgAQCqAQCUAQCWAQDKAQCwAQBuAM4BAKYFAHoA5gEAjAEA
 
 
 
@@ -66,6 +69,9 @@ test 'let binding', fn:
         (local $:pub_name (ref null any))
         (local $:unwrap_x_0 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_1 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_x_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:x (local.get $:cell_x_0))
@@ -93,7 +99,7 @@ test 'let binding', fn:
       (data $d_0 "test")
       (data $d_1 "x")
     )
-    ;; sm:EaQIAJgBAJQBAGABAAGEAQCYAQCiAQCUAQCWAQDGAQCoAQBuAMoBAKYFAHoA5gEAjAEA
+    ;; sm:E_YIAJwBAKYBAJgBAJQBAGABAAGEAQCYAQCiAQCUAQCWAQDGAQCoAQBuAMoBAKYFAHoA5gEAjAEA
 
 
 
@@ -119,6 +125,9 @@ test 'multiple let bindings used', fn:
         (local $:pub_name (ref null any))
         (local $:unwrap_x_0 (ref null any))
         (local $:unwrap_y_1 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_2 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_x_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:x (local.get $:cell_x_0))
@@ -155,7 +164,7 @@ test 'multiple let bindings used', fn:
       (data $d_1 "x")
       (data $d_2 "y")
     )
-    ;; sm:GMQLAJgBAJQBAGAAlAEAYAEAAYIBAJgBAKIBAJQBAJYBAMYBAQwBggEAmAEAogEAlAEAlgEAxgEAqAEAqAEBDAXuBQB6AOYBAIwBAA
+    ;; sm:GpYMAJwBAKYBAJgBAJQBAGAAlAEAYAEAAYIBAJgBAKIBAJQBAJYBAMYBAQwBggEAmAEAogEAlAEAlgEAxgEAqAEAqAEBDAXuBQB6AOYBAIwBAA
 
 
 
@@ -176,6 +185,7 @@ test 'binding rhs is a call', fn:
         (local.set $a_2 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $b_3 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 61))
         (return_call $std/operators.fnk:op_plus (local.get $:ctx_param) (local.get $a_2) (local.get $b_3) (local.get $:ret_6))
       )
       (func $test::v_55 (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -219,6 +229,9 @@ test 'binding rhs is a call', fn:
         (local $:lit_14 (ref null any))
         (local $:lit_15 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_4 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_add_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:add (local.get $:cell_add_0))
@@ -240,6 +253,7 @@ test 'binding rhs is a call', fn:
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_15) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_14) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:v_45) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 21))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_add_0))
       )
       (func $test::host_wrapper (export "test") (type $test::Fn_host_wrapper) (param $:cont (ref null any))
@@ -258,7 +272,7 @@ test 'binding rhs is a call', fn:
       (data $d_1 "x")
       (data $d_2 "add")
     )
-    ;; sm:LoIFAJgBAJoBAJIBAJoBAJIBAR4FwgoAlgEAugEAzgEAugEAxAEAngEAogEAlAEAlgEAxgEArAEAbgDMAQCYDQCYAQCYAQBoAJQBAGAAegDOAQCeAQCqAQCUAQCWAQDKAQDeAQDQAQCwAQEcAYoBAQYBigEAbgDCAQDCAQC-AQC0BQB6AOYBAIwBAA
+    ;; sm:MoIFAJgBAJoBAJIBAJoBAJIBAIIBAR4FwgoAlgEAugEAzgEAugEAxAEAngEAogEAlAEAlgEAxgEArAEAbgDMAQDqDQCcAQCmAQCYAQCYAQBoAJQBAGAAegDOAQCeAQCqAQCUAQCWAQDKAQDeAQDQAQCwAQEcAYoBAQYBigEAbgDCAQDCAQC-AQCCAQC0BQB6AOYBAIwBAA
 
 
 
@@ -280,6 +294,7 @@ test 'top-level rec destructure then fn using binding', fn:
         (local.set $:ret_30 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $a_2 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 100))
         (local.set $:caps_cast (ref.cast (ref $rt/apply.wat:Captures) (local.get $:caps_param)))
         (local.set $:slot_95_raw (array.get $rt/apply.wat:Captures (local.get $:caps_cast) (i32.const 0)))
         (local.set $:slot_95 (ref.cast (ref null $rt/apply.wat:Cell) (local.get $:slot_95_raw)))
@@ -412,6 +427,9 @@ test 'top-level rec destructure then fn using binding', fn:
         (local $:lit_4 (ref null any))
         (local $:lit_5 (ref null any))
         (local $:lit_6 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_3 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_x_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test::x_0 (local.get $:cell_x_0))
@@ -440,6 +458,6 @@ test 'top-level rec destructure then fn using binding', fn:
       (data $d_1 "foo")
       (data $d_2 "x")
     )
-    ;; sm:VL4IAJoBAJoBAJIBALoBAM4BALoBAKwBATQF3AoAlgEAugEAxgEAogEAvAEA0gEAoAEAqgEAlAEAlgEAygEAsAEAbgDOAQD8BgCWAQCaAQCWAQC6AQDIAQBuAL4BAMoIAJYBALoBAMgBAMgBALoBANIBATMNkgEBAA28BgC6AQDIAQBuAMgIAJwBAJoBAJwBAJoBAJQBAOQBANIBALgBANIBAQANtAQAWACkCQCUAQC6AQDGAQC4AQDSAQB6ANIBAHoA0gEAbgC8AQC-AQC-AQCwCQCYAQCUAQBmAJgBAGgAtAEA0gEBDAdgAQIBkAEBBgKKAQEFBewFAHoA5gEAjAEA
+    ;; sm:V74IAJoBAJoBAJIBAIQBALoBAM4BALoBAKwBATQF3AoAlgEAugEAxgEAogEAvAEA0gEAoAEAqgEAlAEAlgEAygEAsAEAbgDOAQD8BgCWAQCaAQCWAQC6AQDIAQBuAL4BAMoIAJYBALoBAMgBAMgBALoBANIBATMNkgEBAA28BgC6AQDIAQBuAMgIAJwBAJoBAJwBAJoBAJQBAOQBANIBALgBANIBAQANtAQAWACkCQCUAQC6AQDGAQC4AQDSAQB6ANIBAHoA0gEAbgC8AQC-AQC-AQCCCgCcAQCmAQCYAQCUAQBmAJgBAGgAtAEA0gEBDAdgAQIBkAEBBgKKAQEFBewFAHoA5gEAjAEA
 
 
diff --git a/src/passes/wasm/test_collections.fnk b/src/passes/wasm/test_collections.fnk
index c5bb608..7dc119f 100644
--- a/src/passes/wasm/test_collections.fnk
+++ b/src/passes/wasm/test_collections.fnk
@@ -84,6 +84,9 @@ test 'list with spread at tail', fn:
         (local $:caps_arg (ref null $rt/apply.wat:Captures))
         (local $:lit_3 (ref null any))
         (local $:lit_4 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_1 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_xs_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:xs (local.get $:cell_xs_0))
@@ -109,7 +112,7 @@ test 'list with spread at tail', fn:
       (data $d_0 "test")
       (data $d_1 "xs")
     )
-    ;; sm:K8AHAJYBALoBAM4BALoBAMQBAK4BARoEiAwAlAEAugEAzgEAugEAxAEAnAEApgEAlAEAlgEAyAEA4gEA0AEBDAGKAQENCXIBDgHSCQCUAQC6AQDOAQC6AQDEAQDiAQDQAQEZAYgBAQABoggAmAEAlgEAZADgAQDQAQEGAYgBAQcGcAEIAcwFAHoA5gEAjAEA
+    ;; sm:LcAHAJYBALoBAM4BALoBAMQBAK4BARoEiAwAlAEAugEAzgEAugEAxAEAnAEApgEAlAEAlgEAyAEA4gEA0AEBDAGKAQENCXIBDgHSCQCUAQC6AQDOAQC6AQDEAQDiAQDQAQEZAYgBAQAB9AgAnAEApgEAmAEAlgEAZADgAQDQAQEGAYgBAQcGcAEIAcwFAHoA5gEAjAEA
 
 
 test 'list with spread at head', fn:
@@ -185,6 +188,9 @@ test 'list with spread at head', fn:
         (local $:caps_arg (ref null $rt/apply.wat:Captures))
         (local $:lit_3 (ref null any))
         (local $:lit_4 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_1 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_xs_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:xs (local.get $:cell_xs_0))
@@ -209,7 +215,7 @@ test 'list with spread at head', fn:
       (data $d_0 "test")
       (data $d_1 "xs")
     )
-    ;; sm:KfgFAJYBALoBAMQBARoBiAEBAAGIDACUAQC6AQDOAQC6AQDEAQCcAQCmAQCUAQCWAQDIAQC2AQDQAQCuAQEBCXIBCATcCQCUAQC6AQDOAQC6AQDEAQDiAQDQAQETAYgBAQABoggAmAEAlgEAZADgAQDQAQEGAYgBAQcGcAEIAcwFAHoA5gEAjAEA
+    ;; sm:K_gFAJYBALoBAMQBARoBiAEBAAGIDACUAQC6AQDOAQC6AQDEAQCcAQCmAQCUAQCWAQDIAQC2AQDQAQCuAQEBCXIBCATcCQCUAQC6AQDOAQC6AQDEAQDiAQDQAQETAYgBAQAB9AgAnAEApgEAmAEAlgEAZADgAQDQAQEGAYgBAQcGcAEIAcwFAHoA5gEAjAEA
 
 
 test 'list with two spreads', fn:
@@ -355,6 +361,9 @@ test 'list with two spreads', fn:
         (local $:caps_arg (ref null $rt/apply.wat:Captures))
         (local $:lit_4 (ref null any))
         (local $:lit_5 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_2 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_a_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:a (local.get $:cell_a_0))
@@ -390,4 +399,4 @@ test 'list with two spreads', fn:
       (data $d_1 "b")
       (data $d_2 "a")
     )
-    ;; sm:Tb4HAJYBALoBAM4BALoBAMQBAKwBAS4Dyg0AlgEAugEAzgEAugEAzgEAugEAxAEAngEAogEAlAEAlgEAxgEA4gEA0AEArAEBAQpyAQwDnAsAlgEAugEAzgEAugEAzgEAugEAxgEAkAIA0AEBFwGKAQEAAb4NAJQBALoBANABAL4BANABAL4BAMYBAJ4BAKIBAJQBAJYBAMYBAJQCANIBAQYBigEBBwZyAQgBmAsAlAEAugEA0AEAvgEA0AEAvgEAxgEAlAIA0gEBGwGIAQEAAYoJAJgBAJQBAGAAlAEAYACIAgDSAQEGAYgBAQcGcAEIAcwFAHoA5gEAjAEA
+    ;; sm:T74HAJYBALoBAM4BALoBAMQBAKwBAS4Dyg0AlgEAugEAzgEAugEAzgEAugEAxAEAngEAogEAlAEAlgEAxgEA4gEA0AEArAEBAQpyAQwDnAsAlgEAugEAzgEAugEAzgEAugEAxgEAkAIA0AEBFwGKAQEAAb4NAJQBALoBANABAL4BANABAL4BAMYBAJ4BAKIBAJQBAJYBAMYBAJQCANIBAQYBigEBBwZyAQgBmAsAlAEAugEA0AEAvgEA0AEAvgEAxgEAlAIA0gEBGwGIAQEAAdwJAJwBAKYBAJgBAJQBAGAAlAEAYACIAgDSAQEGAYgBAQcGcAEIAcwFAHoA5gEAjAEA
diff --git a/src/passes/wasm/test_effects.fnk b/src/passes/wasm/test_effects.fnk
index 741bc8f..2628f89 100644
--- a/src/passes/wasm/test_effects.fnk
+++ b/src/passes/wasm/test_effects.fnk
@@ -32,6 +32,7 @@ test 'set_ctx import + call', fn:
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_28) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_114) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 31))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $set_ctx_0))
       )
       (func $test::v_81 (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -133,6 +134,9 @@ test 'set_ctx import + call', fn:
         (local $:imp_val_set_ctx (ref null any))
         (local $:imp_key_set_ctx (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_2 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_2 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:caps_arg (array.new_fixed $rt/apply.wat:Captures 1 (local.get $:ret_2)))
         (local.set $:v_73 (struct.new $rt/apply.wat:Closure (ref.func $test::v_127) (local.get $:caps_arg)))
@@ -157,4 +161,4 @@ test 'set_ctx import + call', fn:
       (data $d_1 "set_ctx")
       (data $d_2 "test")
     )
-    ;; sm:RYYIAJYBALoBAMYBAQIHXAFSBZIBAG4AwgEAxAEA-gYAlgEAmgEAlgEAugEAxgEAbgC-AQDCCACWAQC6AQDGAQDGAQC4AQDQAQFTIZIBAQAhtgYAugEAxgEAbgDCCACaAQCaAQCaAQCaAQCUAQDgAQDQAQC2AQDQAQEAIbQEAFgApAkAlAEAugEAxgEAuAEA0gEAegDSAQB6ANIBAG4AvAEAvgEAvgEAgAoAmAEAtAEA0gEAZAB-AKQBAJYCAG4AxAEApAUAegDmAQCMAQA
+    ;; sm:SIYIAJYBALoBAMYBAQIHXAFSBZIBAG4AwgEAxAEAggEA-gYAlgEAmgEAlgEAugEAxgEAbgC-AQDCCACWAQC6AQDGAQDGAQC4AQDQAQFTIZIBAQAhtgYAugEAxgEAbgDCCACaAQCaAQCaAQCaAQCUAQDgAQDQAQC2AQDQAQEAIbQEAFgApAkAlAEAugEAxgEAuAEA0gEAegDSAQB6ANIBAG4AvAEAvgEAvgEA0goAnAEApgEAmAEAtAEA0gEAZAB-AKQBAJYCAG4AxAEApAUAegDmAQCMAQA
diff --git a/src/passes/wasm/test_functions.fnk b/src/passes/wasm/test_functions.fnk
index 35412e7..b38d861 100644
--- a/src/passes/wasm/test_functions.fnk
+++ b/src/passes/wasm/test_functions.fnk
@@ -19,6 +19,7 @@ test 'user fn call', fn:
         (local.set $a_1 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $b_2 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 35))
         (return_call $std/operators.fnk:op_plus (local.get $:ctx_param) (local.get $a_1) (local.get $b_2) (local.get $:ret_5))
       )
       (func $test::fink_module (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -33,6 +34,9 @@ test 'user fn call', fn:
         (local $:lit_13 (ref null any))
         (local $:lit_14 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_3 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_add_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:add (local.get $:cell_add_0))
@@ -50,6 +54,7 @@ test 'user fn call', fn:
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_14) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_13) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_3) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 17))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_add_0))
       )
       (func $test::host_wrapper (export "test") (type $test::Fn_host_wrapper) (param $:cont (ref null any))
@@ -65,7 +70,7 @@ test 'user fn call', fn:
       (data $d_0 "test")
       (data $d_1 "add")
     )
-    ;; sm:HIIFAJgBAJoBAJIBAJoBAJIBASIFngsAmAEAmAEAaAB6AM4BAJ4BAKoBAJQBAJYBAMoBALABARQBigEBBgGKAQBuAMIBAMIBAMABALQFAHoA5gEAjAEA
+    ;; sm:IIIFAJgBAJoBAJIBAJoBAJIBAIIBASIF8AsAnAEApgEAmAEAmAEAaAB6AM4BAJ4BAKoBAJQBAJYBAMoBALABARQBigEBBgGKAQBuAMIBAMIBAMABAIIBALQFAHoA5gEAjAEA
 
 
 test 'chained fn calls', fn:
@@ -87,6 +92,7 @@ test 'chained fn calls', fn:
         (local.set $:ret_7 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $x_3 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 89))
         (local.set $:lit_9 (struct.new $std/int.wat:I64 (i64.const 2)))
         (return_call $std/operators.fnk:op_mul (local.get $:ctx_param) (local.get $x_3) (local.get $:lit_9) (local.get $:ret_7))
       )
@@ -97,6 +103,7 @@ test 'chained fn calls', fn:
         (local.set $:ret_15 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $x_4 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 83))
         (local.set $:lit_17 (struct.new $std/int.wat:I64 (i64.const 1)))
         (return_call $std/operators.fnk:op_plus (local.get $:ctx_param) (local.get $x_4) (local.get $:lit_17) (local.get $:ret_15))
       )
@@ -131,6 +138,7 @@ test 'chained fn calls', fn:
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:unwrap_x_68) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_70) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 30))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_inc_69))
       )
       (func $test::fink_module (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -153,6 +161,9 @@ test 'chained fn calls', fn:
         (local $:unwrap_double_0 (ref null any))
         (local $:lit_23 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_5 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_double_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:double (local.get $:cell_double_0))
@@ -181,6 +192,7 @@ test 'chained fn calls', fn:
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_23) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:v_65) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 34))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_double_0))
       )
       (func $test::host_wrapper (export "test") (type $test::Fn_host_wrapper) (param $:cont (ref null any))
@@ -202,7 +214,7 @@ test 'chained fn calls', fn:
       (data $d_2 "double")
       (data $d_3 "inc")
     )
-    ;; sm:PYgFAJgBAJoBAJIBASoBiAEBBwX6BQCaAQCaAQCSAQEwAYoBAQcF3AwAlgEAugEAzgEAugEAzgEAugEAxAEAngEAogEAlAEAlgEAxgEAsAEArAEAbgDMAQDCAQD4EACYAQCeAQB0AJgBAGgAlAEAYAB6AM4BAKQBALYBAJQBAJYBANABAHoA0AEAoAEAqgEAlAEAlgEAygEAjAIA0AEAvAEBJAGKAQBuAMIBAL4BALoFAHoA5gEAjAEA
+    ;; sm:Q4gFAJgBAJoBAJIBAIIBASoBiAEBBwX6BQCaAQCaAQCSAQCCAQEwAYoBAQcF3AwAlgEAugEAzgEAugEAzgEAugEAxAEAngEAogEAlAEAlgEAxgEAsAEArAEAbgDMAQDCAQCCAQDKEQCcAQCmAQCYAQCeAQB0AJgBAGgAlAEAYAB6AM4BAKQBALYBAJQBAJYBANABAHoA0AEAoAEAqgEAlAEAlgEAygEAjAIA0AEAvAEBJAGKAQBuAMIBAL4BAIIBALoFAHoA5gEAjAEA
 
 
 test 'pipe unary', fn:
@@ -223,6 +235,7 @@ test 'pipe unary', fn:
         (local.set $:ret_6 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $x_2 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 79))
         (local.set $:lit_8 (struct.new $std/int.wat:I64 (i64.const 2)))
         (return_call $std/operators.fnk:op_mul (local.get $:ctx_param) (local.get $x_2) (local.get $:lit_8) (local.get $:ret_6))
       )
@@ -233,6 +246,7 @@ test 'pipe unary', fn:
         (local.set $:ret_14 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $x_3 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 73))
         (local.set $:lit_16 (struct.new $std/int.wat:I64 (i64.const 1)))
         (return_call $std/operators.fnk:op_plus (local.get $:ctx_param) (local.get $x_3) (local.get $:lit_16) (local.get $:ret_14))
       )
@@ -274,6 +288,9 @@ test 'pipe unary', fn:
         (local $:unwrap_double_0 (ref null any))
         (local $:lit_21 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_4 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_double_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:double (local.get $:cell_double_0))
@@ -318,7 +335,7 @@ test 'pipe unary', fn:
       (data $d_1 "double")
       (data $d_2 "inc")
     )
-    ;; sm:M4gFAJgBAJoBAJIBASoBiAEBBwX6BQCaAQCaAQCSAQEwAYoBAQcF8AgAlgEAugEAzgEAugEAxAEAsAEAbgC-AQDCAQCOEACYAQCeAQB0AJgBAGgAegDOAQCkAQC2AQCUAQCWAQDQAQB6ANABAKABAKoBAJQBAJYBAMoBAOIBANABALwBAQ4BigEAbgDCAQC-AQC6BQB6AOYBAIwBAA
+    ;; sm:N4gFAJgBAJoBAJIBAIIBASoBiAEBBwX6BQCaAQCaAQCSAQCCAQEwAYoBAQcF8AgAlgEAugEAzgEAugEAxAEAsAEAbgC-AQDCAQDgEACcAQCmAQCYAQCeAQB0AJgBAGgAegDOAQCkAQC2AQCUAQCWAQDQAQB6ANABAKABAKoBAJQBAJYBAMoBAOIBANABALwBAQ4BigEAbgDCAQC-AQC6BQB6AOYBAIwBAA
 
 
 test 'match literal first arm', fn:
@@ -511,6 +528,9 @@ test 'match literal first arm', fn:
         (local $:caps_arg (ref null $rt/apply.wat:Captures))
         (local $:lit_1 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:caps_arg (ref.null $rt/apply.wat:Captures))
         (local.set $:v_25 (struct.new $rt/apply.wat:Closure (ref.func $test::v_190) (local.get $:caps_arg)))
@@ -539,7 +559,7 @@ test 'match literal first arm', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:aIgFAJoBARwCjAEAbgDCAQC4BgC6AQDCAQDIAQBuAMYBALIIAJYBALoBAMgBAMgBAIYBAHwAwgwAmgEAmgEAmgEAmgEAlAEA4AEA1AEBBQGKAQEAAdYKAJoBAJoBAJoBAJoBAJQBALoBAMIBAN4BANIBAHoA0gEAbgC8AQDCAQC-AQDIBQCaAQEWAowBAG4AwgEAxAcAnAEAmgEAnAEAmgEAlgEAugEAwgEAbgDEAQCABABYAIQHALoBAMIBAMYBAMIBAHoA1AEAbgDAAQDAAQDEAQD0CACaAQCaAQCWAQC6AQDCAQDCAQCEAgDUAQBuAL4BAMABAMIBAOAMAJgBAHoA0gEAsgEA0gEAegDSAQCyAQDSAQDYAQDSAQEfAYgBAG4AwAEAwAEApAUAegDmAQCMAQA
+    ;; sm:aogFAJoBARwCjAEAbgDCAQC4BgC6AQDCAQDIAQBuAMYBALIIAJYBALoBAMgBAMgBAIYBAHwAwgwAmgEAmgEAmgEAmgEAlAEA4AEA1AEBBQGKAQEAAdYKAJoBAJoBAJoBAJoBAJQBALoBAMIBAN4BANIBAHoA0gEAbgC8AQDCAQC-AQDIBQCaAQEWAowBAG4AwgEAxAcAnAEAmgEAnAEAmgEAlgEAugEAwgEAbgDEAQCABABYAIQHALoBAMIBAMYBAMIBAHoA1AEAbgDAAQDAAQDEAQD0CACaAQCaAQCWAQC6AQDCAQDCAQCEAgDUAQBuAL4BAMABAMIBALINAJwBAKYBAJgBAHoA0gEAsgEA0gEAegDSAQCyAQDSAQDYAQDSAQEfAYgBAG4AwAEAwAEApAUAegDmAQCMAQA
 
 
 test 'match with binding', fn:
@@ -743,6 +763,9 @@ test 'match with binding', fn:
         (local $:caps_arg (ref null $rt/apply.wat:Captures))
         (local $:unwrap_x_0 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_1 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_x_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:x (local.get $:cell_x_0))
@@ -782,7 +805,7 @@ test 'match with binding', fn:
       (data $d_0 "test")
       (data $d_1 "x")
     )
-    ;; sm:cogFAJoBASgBigEAbgDCAQC4BgC6AQDCAQDIAQBuAMYBALIIAJYBALoBAMgBAMgBAIYBAHwAxAwAmgEAmgEAnAEAmgEAlAEA4gEA1AEBBQGKAQEAAdYKAJoBAJoBAJoBAJoBAJQBALoBAMIBAN4BANIBAHoA0gEAbgC8AQDCAQC-AQCKCACaAQC6AQDQAQC-AQCwAQEcAYoBAQcFiAgAnAEAmgEAnAEAmgEAlgEAugEAwgEAbgDEAQCABABYAIQHALoBAMIBAMYBAMIBAHoA1AEAbgDAAQDAAQDEAQD0CACaAQCaAQCWAQC6AQDCAQDCAQCEAgDUAQBuAL4BAMABAMIBAPQPAJgBAJQBAGABNQGCAQCYAQCiAQCUAQCWAQDGAQB6ANIBALIBANIBALYBANIBALIBANIBANgBANIBAKgBAG4AygEAwAEApAUAegDmAQCMAQA
+    ;; sm:dIgFAJoBASgBigEAbgDCAQC4BgC6AQDCAQDIAQBuAMYBALIIAJYBALoBAMgBAMgBAIYBAHwAxAwAmgEAmgEAnAEAmgEAlAEA4gEA1AEBBQGKAQEAAdYKAJoBAJoBAJoBAJoBAJQBALoBAMIBAN4BANIBAHoA0gEAbgC8AQDCAQC-AQCKCACaAQC6AQDQAQC-AQCwAQEcAYoBAQcFiAgAnAEAmgEAnAEAmgEAlgEAugEAwgEAbgDEAQCABABYAIQHALoBAMIBAMYBAMIBAHoA1AEAbgDAAQDAAQDEAQD0CACaAQCaAQCWAQC6AQDCAQDCAQCEAgDUAQBuAL4BAMABAMIBAMYQAJwBAKYBAJgBAJQBAGABNQGCAQCYAQCiAQCUAQCWAQDGAQB6ANIBALIBANIBALYBANIBALIBANIBANgBANIBAKgBAG4AygEAwAEApAUAegDmAQCMAQA
 
 
 test 'simple recursion', fn:
@@ -906,6 +929,7 @@ test 'simple recursion', fn:
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:v_50) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_171) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 54))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_recurse_170))
       )
       (func $test::v_223 (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -1012,6 +1036,7 @@ test 'simple recursion', fn:
         (local.set $:ret_4 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $n_1 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 245))
         (local.set $:caps_cast (ref.cast (ref $rt/apply.wat:Captures) (local.get $:caps_param)))
         (local.set $:slot_240_raw (array.get $rt/apply.wat:Captures (local.get $:caps_cast) (i32.const 0)))
         (local.set $:slot_240 (ref.cast (ref null $rt/apply.wat:Cell) (local.get $:slot_240_raw)))
@@ -1041,6 +1066,9 @@ test 'simple recursion', fn:
         (local $:unwrap_recurse_0 (ref null any))
         (local $:lit_91 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_2 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_recurse_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:recurse (local.get $:cell_recurse_0))
@@ -1056,6 +1084,7 @@ test 'simple recursion', fn:
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_91) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_2) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 94))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_recurse_0))
       )
       (func $test::host_wrapper (export "test") (type $test::Fn_host_wrapper) (param $:cont (ref null any))
@@ -1074,7 +1103,7 @@ test 'simple recursion', fn:
       (data $d_0 "test")
       (data $d_1 "recurse")
     )
-    ;; sm:igGIBQCaAQFEAowBAG4AwgEAuAYAugEAwgEAyAEAbgDGAQCyCACWAQC6AQDIAQDIAQCGAQB8AMgMAJwBAJoBAJwBAJoBAJYBAOQBANQBAQUBigEBAAHYCgCaAQCaAQCaAQCaAQCUAQC6AQDCAQDeAQDSAQB6ANIBAG4AvAEAwgEAvgEAzggAlgEAugEA0AEAvgEAxgEAvAEAbgC-AQDEAQDOCQCaAQC6AQDQAQC-AQDAAQDkAQDUAQEyAYoBAQcF-AcAnAEAmgEAnAEAmgEAlgEAugEAwgEAbgDEAQCABABYAIQHALoBAMIBAMYBAMIBAHoA1AEAbgDAAQDAAQDEAQD0CACaAQCaAQCWAQC6AQDCAQDCAQCEAgDUAQBuAL4BAMABAMIBAPYOAJgBAJoBAJIBALoBANABAL4BAHoA0gEAsgEA0gEA3AEA0gEAsgEA0gEA2AEA0gEAbgC6AQDAAQDECgCYAQCgAQB4AMIBANABAKYBALoBAJQBAJYBANIBAMABARwBigEAbgDCAQDAAQC8BQB6AOYBAIwBAA
+    ;; sm:jwGIBQCaAQFEAowBAG4AwgEAuAYAugEAwgEAyAEAbgDGAQCyCACWAQC6AQDIAQDIAQCGAQB8AMgMAJwBAJoBAJwBAJoBAJYBAOQBANQBAQUBigEBAAHYCgCaAQCaAQCaAQCaAQCUAQC6AQDCAQDeAQDSAQB6ANIBAG4AvAEAwgEAvgEAzggAlgEAugEA0AEAvgEAxgEAvAEAbgC-AQDEAQCCAQDOCQCaAQC6AQDQAQC-AQDAAQDkAQDUAQEyAYoBAQcF-AcAnAEAmgEAnAEAmgEAlgEAugEAwgEAbgDEAQCABABYAIQHALoBAMIBAMYBAMIBAHoA1AEAbgDAAQDAAQDEAQD0CACaAQCaAQCWAQC6AQDCAQDCAQCEAgDUAQBuAL4BAMABAMIBAPYOAJgBAJoBAJIBAIQBALoBANABAL4BAHoA0gEAsgEA0gEA3AEA0gEAsgEA0gEA2AEA0gEAbgC6AQDAAQCWCwCcAQCmAQCYAQCgAQB4AMIBANABAKYBALoBAJQBAJYBANIBAMABARwBigEAbgDCAQDAAQCCAQC8BQB6AOYBAIwBAA
 
 
 test 'mutual recursion — ping pong', fn:
@@ -1096,6 +1125,7 @@ test 'mutual recursion — ping pong', fn:
         (local.set $:ret_6 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $x_2 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 63))
         (local.set $:caps_cast (ref.cast (ref $rt/apply.wat:Captures) (local.get $:caps_param)))
         (local.set $:slot_58_raw (array.get $rt/apply.wat:Captures (local.get $:caps_cast) (i32.const 0)))
         (local.set $:slot_58 (ref.cast (ref null $rt/apply.wat:Cell) (local.get $:slot_58_raw)))
@@ -1103,6 +1133,7 @@ test 'mutual recursion — ping pong', fn:
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $x_2) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_6) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 11))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_pong_58))
       )
       (func $test::v_55 (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -1116,6 +1147,7 @@ test 'mutual recursion — ping pong', fn:
         (local.set $:ret_14 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $x_3 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 55))
         (local.set $:caps_cast (ref.cast (ref $rt/apply.wat:Captures) (local.get $:caps_param)))
         (local.set $:slot_50_raw (array.get $rt/apply.wat:Captures (local.get $:caps_cast) (i32.const 0)))
         (local.set $:slot_50 (ref.cast (ref null $rt/apply.wat:Cell) (local.get $:slot_50_raw)))
@@ -1123,6 +1155,7 @@ test 'mutual recursion — ping pong', fn:
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $x_3) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_14) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 19))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_ping_50))
       )
       (func $test::fink_module (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -1142,6 +1175,9 @@ test 'mutual recursion — ping pong', fn:
         (local $:unwrap_ping_0 (ref null any))
         (local $:lit_22 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_4 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_ping_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:ping (local.get $:cell_ping_0))
@@ -1166,6 +1202,7 @@ test 'mutual recursion — ping pong', fn:
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_22) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_4) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 25))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_ping_0))
       )
       (func $test::host_wrapper (export "test") (type $test::Fn_host_wrapper) (param $:cont (ref null any))
@@ -1185,7 +1222,7 @@ test 'mutual recursion — ping pong', fn:
       (data $d_1 "ping")
       (data $d_2 "pong")
     )
-    ;; sm:M_gHAJgBAJoBAJIBALoBAM4BALoBALIBAG4AugEAwAEAzggAmgEAmgEAkgEAugEAzgEAugEAsgEAbgC6AQDCAQDSDgCYAQCaAQBsAJoBAGwAvAEAzgEAoAEArgEAlAEAlgEAzAEAvAEA0AEAogEArgEAlAEAlgEAzAEAtAEBWgGKAQBuAMIBAMABALYFAHoA5gEAjAEA
+    ;; sm:OvgHAJgBAJoBAJIBAIIBALoBAM4BALoBALIBAG4AugEAwAEAggEAzggAmgEAmgEAkgEAggEAugEAzgEAugEAsgEAbgC6AQDCAQCCAQCkDwCcAQCmAQCYAQCaAQBsAJoBAGwAvAEAzgEAoAEArgEAlAEAlgEAzAEAvAEA0AEAogEArgEAlAEAlgEAzAEAtAEBWgGKAQBuAMIBAMABAIIBALYFAHoA5gEAjAEA
 
 
 test 'mutual recursion — is_even / is_odd', fn:
@@ -1312,6 +1349,7 @@ test 'mutual recursion — is_even / is_odd', fn:
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:v_52) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_305) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 56))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_is_odd_304))
       )
       (func $test::v_357 (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -1418,6 +1456,7 @@ test 'mutual recursion — is_even / is_odd', fn:
         (local.set $:ret_6 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $n_2 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 483))
         (local.set $:caps_cast (ref.cast (ref $rt/apply.wat:Captures) (local.get $:caps_param)))
         (local.set $:slot_478_raw (array.get $rt/apply.wat:Captures (local.get $:caps_cast) (i32.const 0)))
         (local.set $:slot_478 (ref.cast (ref null $rt/apply.wat:Cell) (local.get $:slot_478_raw)))
@@ -1546,6 +1585,7 @@ test 'mutual recursion — is_even / is_odd', fn:
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:v_139) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_401) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 143))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_is_even_400))
       )
       (func $test::v_453 (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -1652,6 +1692,7 @@ test 'mutual recursion — is_even / is_odd', fn:
         (local.set $:ret_93 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $n_3 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 475))
         (local.set $:caps_cast (ref.cast (ref $rt/apply.wat:Captures) (local.get $:caps_param)))
         (local.set $:slot_470_raw (array.get $rt/apply.wat:Captures (local.get $:caps_cast) (i32.const 0)))
         (local.set $:slot_470 (ref.cast (ref null $rt/apply.wat:Cell) (local.get $:slot_470_raw)))
@@ -1687,6 +1728,9 @@ test 'mutual recursion — is_even / is_odd', fn:
         (local $:unwrap_is_even_0 (ref null any))
         (local $:lit_180 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_4 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_is_even_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:is_even (local.get $:cell_is_even_0))
@@ -1711,6 +1755,7 @@ test 'mutual recursion — is_even / is_odd', fn:
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_180) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_4) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 183))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_is_even_0))
       )
       (func $test::host_wrapper (export "test") (type $test::Fn_host_wrapper) (param $:cont (ref null any))
@@ -1734,7 +1779,7 @@ test 'mutual recursion — is_even / is_odd', fn:
       (data $d_1 "is_even")
       (data $d_2 "is_odd")
     )
-    ;; sm:iQKIBQCaAQFEBGIAbgDCAQC4BgC6AQDCAQDIAQBuAMYBALIIAJYBALoBAMgBAMgBAIYBAHwAyAwAnAEAmgEAnAEAmgEAlgEA5AEA1AEBBQGKAQEAAdoKAJoBAJoBAJwBAJoBAJQBALoBAMIBAN4BANIBAHoA0gEAbgC8AQDEAQC-AQDMCACWAQC6AQDQAQC-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-AgAnAEAmgEAmAEAugEAwgEAwgEAiAIA1AEAbgDAAQDAAQDEAQCCDwCaAQCaAQCSAQC6AQDQAQC-AQB6ANQBALQBANQBANwBANQBALQBANQBANwBANQBAG4AugEAwgEA3A4AmAEAoAEAeACeAQB0AMABANABAKYBALoBAJQBAJYBANIBAMIBANIBAKYBALYBAJQBAJYBANABAMABARwBjAEAbgDEAQDAAQC8BQB6AOYBAIwBAA
+    ;; sm:kAKIBQCaAQFEBGIAbgDCAQC4BgC6AQDCAQDIAQBuAMYBALIIAJYBALoBAMgBAMgBAIYBAHwAyAwAnAEAmgEAnAEAmgEAlgEA5AEA1AEBBQGKAQEAAdoKAJoBAJoBAJwBAJoBAJQBALoBAMIBAN4BANIBAHoA0gEAbgC8AQDEAQC-AQDMCACWAQC6AQDQAQC-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-AgAnAEAmgEAmAEAugEAwgEAwgEAiAIA1AEAbgDAAQDAAQDEAQCCDwCaAQCaAQCSAQCEAQC6AQDQAQC-AQB6ANQBALQBANQBANwBANQBALQBANQBANwBANQBAG4AugEAwgEArg8AnAEApgEAmAEAoAEAeACeAQB0AMABANABAKYBALoBAJQBAJYBANIBAMIBANIBAKYBALYBAJQBAJYBANABAMABARwBjAEAbgDEAQDAAQCEAQC8BQB6AOYBAIwBAA
 
 
 test 'closure construction and call', fn:
@@ -1754,6 +1799,7 @@ test 'closure construction and call', fn:
         (local.set $:ret_8 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $y_3 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 59))
         (local.set $:caps_cast (ref.cast (ref $rt/apply.wat:Captures) (local.get $:caps_param)))
         (local.set $x_54 (array.get $rt/apply.wat:Captures (local.get $:caps_cast) (i32.const 0)))
         (return_call $std/operators.fnk:op_plus (local.get $:ctx_param) (local.get $x_54) (local.get $y_3) (local.get $:ret_8))
@@ -1767,8 +1813,10 @@ test 'closure construction and call', fn:
         (local.set $:ret_6 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $x_2 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 79))
         (local.set $:caps_arg (array.new_fixed $rt/apply.wat:Captures 1 (local.get $x_2)))
         (local.set $:v_7 (struct.new $rt/apply.wat:Closure (ref.func $test::v_59) (local.get $:caps_arg)))
+        (call $rt/trace.wat:trace_pop (i32.const 0) (i32.const 79))
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:v_7) (local.get $:args)))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:ret_6))
@@ -1800,6 +1848,7 @@ test 'closure construction and call', fn:
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_22) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_67) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 25))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_add1_66))
       )
       (func $test::fink_module (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -1816,6 +1865,9 @@ test 'closure construction and call', fn:
         (local $:unwrap_add_0 (ref null any))
         (local $:lit_18 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_4 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_add_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:add (local.get $:cell_add_0))
@@ -1835,6 +1887,7 @@ test 'closure construction and call', fn:
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_18) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:v_51) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 29))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_add_0))
       )
       (func $test::host_wrapper (export "test") (type $test::Fn_host_wrapper) (param $:cont (ref null any))
@@ -1853,7 +1906,7 @@ test 'closure construction and call', fn:
       (data $d_1 "add1")
       (data $d_2 "add")
     )
-    ;; sm:Nu4FAJgBAJoBAJIBALoBAL4BASgFnAcAmAEAmgEAkgEArgEAzgEAbgC8AQDuCgCWAQC6AQDOAQC6AQDEAQCeAQCuAQCUAQCWAQDMAQCyAQEwAYoBAG4AwgEAwgEA5gwAmAEAmAEAaACaAQBsAHoAzgEAngEAqgEAlAEAlgEAygEA5AEA0AEAsAEBDQGKAQBuAMIBAL4BALQFAHoA5gEAjAEA
+    ;; sm:Pe4FAJgBAJoBAJIBAIIBALoBAL4BASgFnAcAmAEAmgEAkgEAggEArgEAzgEAgAEAbgC8AQDuCgCWAQC6AQDOAQC6AQDEAQCeAQCuAQCUAQCWAQDMAQCyAQEwAYoBAG4AwgEAwgEAggEAuA0AnAEApgEAmAEAmAEAaACaAQBsAHoAzgEAngEAqgEAlAEAlgEAygEA5AEA0AEAsAEBDQGKAQBuAMIBAL4BAIIBALQFAHoA5gEAjAEA
 
 
 test 'self-recursive fn defined inside another fn', fn:
@@ -1981,6 +2034,7 @@ test 'self-recursive fn defined inside another fn', fn:
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:v_54) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_188) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 58))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_inner_187))
       )
       (func $test::v_240 (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -2088,6 +2142,7 @@ test 'self-recursive fn defined inside another fn', fn:
         (local.set $:ret_8 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $n_3 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 266))
         (local.set $:caps_cast (ref.cast (ref $rt/apply.wat:Captures) (local.get $:caps_param)))
         (local.set $x_259 (array.get $rt/apply.wat:Captures (local.get $:caps_cast) (i32.const 0)))
         (local.set $:slot_260_raw (array.get $rt/apply.wat:Captures (local.get $:caps_cast) (i32.const 1)))
@@ -2119,6 +2174,7 @@ test 'self-recursive fn defined inside another fn', fn:
         (local.set $:ret_6 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $x_1 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 272))
         (local.set $:cell_inner_2 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test::inner_2 (local.get $:cell_inner_2))
         (local.set $:caps_arg (array.new_fixed $rt/apply.wat:Captures 2 (local.get $x_1) (global.get $test::inner_2)))
@@ -2129,6 +2185,7 @@ test 'self-recursive fn defined inside another fn', fn:
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_95) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_6) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 98))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_inner_2))
       )
       (func $test::fink_module (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -2142,6 +2199,9 @@ test 'self-recursive fn defined inside another fn', fn:
         (local $:unwrap_outer_0 (ref null any))
         (local $:lit_106 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_4 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_outer_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:outer (local.get $:cell_outer_0))
@@ -2157,6 +2217,7 @@ test 'self-recursive fn defined inside another fn', fn:
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_106) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_4) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 109))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_outer_0))
       )
       (func $test::host_wrapper (export "test") (type $test::Fn_host_wrapper) (param $:cont (ref null any))
@@ -2176,7 +2237,7 @@ test 'self-recursive fn defined inside another fn', fn:
       (data $d_0 "test")
       (data $d_1 "outer")
     )
-    ;; sm:mgHuBQCaAQC6AQDAAQBuAL4BALgGALoBAMIBAMgBAG4AxgEAsggAlgEAugEAyAEAyAEAhgEAfADIDACcAQCaAQCcAQCaAQCWAQDkAQDUAQFiAYoBAQAB3goAnAEAmgEAnAEAmgEAlgEAugEAwgEA4AEA0gEAegDSAQBuAL4BAMQBAL4BAMoIAJYBALoBANABAL4BAMYBALgBAG4AvgEAxAEAygkAmgEAugEA0AEAvgEAwAEA5AEA1AEBMAGKAQEHBfgHAJwBAJoBAJwBAJoBAJYBALoBAMIBAG4AxAEAgAQAWACEBwC6AQDCAQDGAQDCAQB6ANQBAG4AwAEAwAEAxAEA9AgAmgEAmgEAlgEAugEAwgEAwgEAhAIA1AEAbgC-AQDAAQDCAQC6DwCYAQCaAQCSAQC6AQDAAQDQAQC-AQCyAQDSAQCyAQDSAQDcAQDSAQCyAQDSAQDYAQDSAQBuALoBAMABAIQJAJgBAJoBAJIBAJwBAHYA5gEA0AEAqAEAvgEBHAGKAQBuAMIBAMABAM4KAJgBAJwBAHAAegDQAQCiAQCyAQCUAQCWAQDOAQC4AQESAo4BAG4AxAEAwAEAuAUAegDmAQCMAQA
+    ;; sm:oQHuBQCaAQC6AQDAAQBuAL4BALgGALoBAMIBAMgBAG4AxgEAsggAlgEAugEAyAEAyAEAhgEAfADIDACcAQCaAQCcAQCaAQCWAQDkAQDUAQFiAYoBAQAB3goAnAEAmgEAnAEAmgEAlgEAugEAwgEA4AEA0gEAegDSAQBuAL4BAMQBAL4BAMoIAJYBALoBANABAL4BAMYBALgBAG4AvgEAxAEAggEAygkAmgEAugEA0AEAvgEAwAEA5AEA1AEBMAGKAQEHBfgHAJwBAJoBAJwBAJoBAJYBALoBAMIBAG4AxAEAgAQAWACEBwC6AQDCAQDGAQDCAQB6ANQBAG4AwAEAwAEAxAEA9AgAmgEAmgEAlgEAugEAwgEAwgEAhAIA1AEAbgC-AQDAAQDCAQC6DwCYAQCaAQCSAQCEAQC6AQDAAQDQAQC-AQCyAQDSAQCyAQDSAQDcAQDSAQCyAQDSAQDYAQDSAQBuALoBAMABAIQJAJgBAJoBAJIBAIQBAJwBAHYA5gEA0AEAqAEAvgEBHAGKAQBuAMIBAMABAIIBAKALAJwBAKYBAJgBAJwBAHAAegDQAQCiAQCyAQCUAQCWAQDOAQC4AQESAo4BAG4AxAEAwAEAhAEAuAUAegDmAQCMAQA
 
 
 # TODO, duplicate?
@@ -2334,6 +2395,7 @@ test 'recursive list sum', fn:
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:v_85) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $rest_307) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_306) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 89))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_sum_305))
       )
       (func $test::v_402 (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -2541,6 +2603,7 @@ test 'recursive list sum', fn:
         (local.set $items_1 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $c_2 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 466))
         (local.set $:caps_cast (ref.cast (ref $rt/apply.wat:Captures) (local.get $:caps_param)))
         (local.set $:slot_461_raw (array.get $rt/apply.wat:Captures (local.get $:caps_cast) (i32.const 0)))
         (local.set $:slot_461 (ref.cast (ref null $rt/apply.wat:Cell) (local.get $:slot_461_raw)))
@@ -2579,6 +2642,7 @@ test 'recursive list sum', fn:
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_151) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:v_149) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_422) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 154))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_sum_421))
       )
       (func $test::v_438 (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -2650,6 +2714,9 @@ test 'recursive list sum', fn:
         (local $:caps_arg (ref null $rt/apply.wat:Captures))
         (local $:lit_141 (ref null any))
         (local $:lit_142 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_5 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_sum_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:sum (local.get $:cell_sum_0))
@@ -2686,7 +2753,7 @@ test 'recursive list sum', fn:
       (data $d_0 "test")
       (data $d_1 "sum")
     )
-    ;; sm: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-AQDGAQC0AQFgAYwBAG4AxAEAwAEAxAEAzAkAmAEAugEA0AEAvgEAxgEA5gEA1AEBGQGMAQEAAeYJAJgBALoBANABAL4BAMYBAOYBANQBAQYBjAEBAAHmCQCYAQC6AQDQAQC-AQDGAQDmAQDUAQEGAYwBAQAB0AsAmAEAmAEAaAC6AQDQAQCeAQCqAQCUAQCWAQDKAQDiAQDUAQEGAYwBARMMdAEUAdYFAHoA5gEAjAEA
+    ;; sm:_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-AQDGAQC0AQFgAYwBAG4AxAEAwAEAxAEAhAEAzAkAmAEAugEA0AEAvgEAxgEA5gEA1AEBGQGMAQEAAeYJAJgBALoBANABAL4BAMYBAOYBANQBAQYBjAEBAAHmCQCYAQC6AQDQAQC-AQDGAQDmAQDUAQEGAYwBAQABogwAnAEApgEAmAEAmAEAaAC6AQDQAQCeAQCqAQCUAQCWAQDKAQDiAQDUAQEGAYwBARMMdAEUAdYFAHoA5gEAjAEA
 
 
 
@@ -2705,6 +2772,8 @@ test 'main returns exit code', fn:
         (local $:lit_4 (ref null any))
         (local $:args (ref any))
         (local.set $:ret_3 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 28))
+        (call $rt/trace.wat:trace_pop (i32.const 0) (i32.const 28))
         (local.set $:lit_4 (struct.new $std/int.wat:I64 (i64.const 0)))
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_4) (local.get $:args)))
@@ -2720,6 +2789,9 @@ test 'main returns exit code', fn:
         (local $:pub_name (ref null any))
         (local $:unwrap_main_0 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_1 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_main_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:main (local.get $:cell_main_0))
@@ -2748,4 +2820,4 @@ test 'main returns exit code', fn:
       (data $d_0 "test")
       (data $d_1 "main")
     )
-    ;; sm:F4IFAJgBARoBiAEAbgDAAQDsCQCYAQCaAQBsAHoAzgEAoAEArgEAlAEAlgEAzAEAtAEAbgDQAQCmBQB6AOYBAIwBAA
+    ;; sm:G4IFAJgBAIIBAIABARoBiAEAbgDAAQC-CgCcAQCmAQCYAQCaAQBsAHoAzgEAoAEArgEAlAEAlgEAzAEAtAEAbgDQAQCmBQB6AOYBAIwBAA
diff --git a/src/passes/wasm/test_io.fnk b/src/passes/wasm/test_io.fnk
index 52299d4..45f1076 100644
--- a/src/passes/wasm/test_io.fnk
+++ b/src/passes/wasm/test_io.fnk
@@ -31,6 +31,7 @@ test 'std io import handling', fn:
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:v_82) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $stderr_198) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_197) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 86))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $write_196))
       )
       (func $test::v_219 (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -88,6 +89,7 @@ test 'std io import handling', fn:
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:v_73) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $stdout_226) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:v_163) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 92))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $write_222))
       )
       (func $test::v_249 (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -163,6 +165,7 @@ test 'std io import handling', fn:
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_66) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $stdin_2) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:v_169) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 98))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $read_3))
       )
       (func $test::v_265 (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -368,6 +371,9 @@ test 'std io import handling', fn:
         (local $:imp_url (ref null any))
         (local $:imp_caps_arg (ref null $rt/apply.wat:Captures))
         (local $:imp_mod_clos (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_1 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_7 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_ham_5 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:ham (local.get $:cell_ham_5))
@@ -401,4 +407,4 @@ test 'std io import handling', fn:
       (data $d_8 "stdout")
       (data $d_9 "std/io.fnk")
     )
-    ;; sm: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
+    ;; sm: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
diff --git a/src/passes/wasm/test_linking.fnk b/src/passes/wasm/test_linking.fnk
index 461d455..2cd55b7 100644
--- a/src/passes/wasm/test_linking.fnk
+++ b/src/passes/wasm/test_linking.fnk
@@ -28,6 +28,7 @@ test 'multi module import', fn:
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_28) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_114) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 31))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $shrub_0))
       )
       (func $./test.fnk::v_81 (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -127,6 +128,9 @@ test 'multi module import', fn:
         (local $:imp_url (ref null any))
         (local $:imp_caps_arg (ref null $rt/apply.wat:Captures))
         (local $:imp_mod_clos (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_2 10)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_2 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:caps_arg (array.new_fixed $rt/apply.wat:Captures 1 (local.get $:ret_2)))
         (local.set $:v_73 (struct.new $rt/apply.wat:Closure (ref.func $./test.fnk::v_127) (local.get $:caps_arg)))
@@ -153,11 +157,13 @@ test 'multi module import', fn:
         (local.set $:ret_30 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $ham_3 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 1) (i32.const 100))
         (local.set $:caps_cast (ref.cast (ref $rt/apply.wat:Captures) (local.get $:caps_param)))
         (local.set $foo_95 (array.get $rt/apply.wat:Captures (local.get $:caps_cast) (i32.const 0)))
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $ham_3) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_30) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 1) (i32.const 35))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $foo_95))
       )
       (func $./test_link/simple.fnk::v_146 (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -286,6 +292,9 @@ test 'multi module import', fn:
         (local $:imp_url (ref null any))
         (local $:imp_caps_arg (ref null $rt/apply.wat:Captures))
         (local $:imp_mod_clos (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_3 22)))
+        (call $rt/modules.wat:register_module (i32.const 1) (local.get $:mod_reg_url))
         (local.set $:ret_4 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_shrub_1 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $./test_link/simple.fnk:shrub (local.get $:cell_shrub_1))
@@ -312,6 +321,7 @@ test 'multi module import', fn:
         (local.set $:ret_4 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $ni_1 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 2) (i32.const 31))
         (local.set $:lit_6 (struct.new $std/int.wat:I64 (i64.const 2)))
         (return_call $std/operators.fnk:op_mul (local.get $:ctx_param) (local.get $ni_1) (local.get $:lit_6) (local.get $:ret_4))
       )
@@ -325,6 +335,9 @@ test 'multi module import', fn:
         (local $:pub_name (ref null any))
         (local $:unwrap_foo_0 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_7 27)))
+        (call $rt/modules.wat:register_module (i32.const 2) (local.get $:mod_reg_url))
         (local.set $:ret_2 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_foo_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $./test_link/foobar/spam.fnk:foo (local.get $:cell_foo_0))
@@ -361,7 +374,7 @@ test 'multi module import', fn:
       (data $d_7 "./test_link/foobar/spam.fnk")
       (data $d_8 "foo")
     )
-    ;; sm:rAHmCwCWAQC6AQDGAQECBVgBXgKMAQBuAMIBAMQBAIIHAJYBAJoBAJYBALoBAMYBAG4AvgEAzggAlgEAugEAxgEAxgEAuAEA3AEBXymSAQEAKcIGALoBAMYBAG4AzggAmgEAmgEAmgEAmgEAlAEA4AEA3AEAtgEA3AEBACnABABYALAJAJQBALoBAMYBALgBAN4BAHoA3gEAegDeAQBuALwBAL4BAL4BAKoIAJgBALQBAN4BAJYBAIIBAJoCAIgGAHoA8gEAjgEAogcAmgEAmgEAlgEAugEAwgEAbgC-AQDCAQCQCwCWAQC6AQDGAQECA1QAsgEA9gEAyAEA1gEAlgEAlgEAzgEA3AEAbgDSAQCgBwCWAQCaAQCWAQC6AQDIAQBuAL4BAO4IAJYBALoBAMgBAMgBALoBAPYBAQEikgEBACLgBgC6AQDIAQBuAOwIAJwBAJoBAJwBAJoBAJQBAOQBAPYBALgBAPYBAQAi2AQAWADICQCUAQC6AQDGAQC4AQD2AQB6APYBAHoA9gEAbgC8AQC-AQC-AQC0CQCYAQCcAQCUAQC0AQD2AQCWAQCCAQCkAgDQBgB6AIoCAI4BAIIGAJgBAJoBAJQBASgBiAEBCQbCCgCYAQCYAQCWAQB6APwBAMwBANgBAJYBAJYBAMoBAN4BAG4AzgEAsAYAegCUAgCOAQA
+    ;; sm:tgHmCwCWAQC6AQDGAQECBVgBXgKMAQBuAMIBAMQBAIIBAIIHAJYBAJoBAJYBALoBAMYBAG4AvgEAzggAlgEAugEAxgEAxgEAuAEA3AEBXymSAQEAKcIGALoBAMYBAG4AzggAmgEAmgEAmgEAmgEAlAEA4AEA3AEAtgEA3AEBACnABABYALAJAJQBALoBAMYBALgBAN4BAHoA3gEAegDeAQBuALwBAL4BAL4BAPwIAJ4BAKYBAJgBALQBAN4BAJYBAIIBAJoCAIgGAHoA8gEAjgEAogcAmgEAmgEAlgEAhAEAugEAwgEAbgC-AQDCAQCCAQCQCwCWAQC6AQDGAQECA1QAsgEA9gEAyAEA1gEAlgEAlgEAzgEA3AEAbgDSAQCgBwCWAQCaAQCWAQC6AQDIAQBuAL4BAO4IAJYBALoBAMgBAMgBALoBAPYBAQEikgEBACLgBgC6AQDIAQBuAOwIAJwBAJoBAJwBAJoBAJQBAOQBAPYBALgBAPYBAQAi2AQAWADICQCUAQC6AQDGAQC4AQD2AQB6APYBAHoA9gEAbgC8AQC-AQC-AQCGCgCeAQCmAQCYAQCcAQCUAQC0AQD2AQCWAQCCAQCkAgDQBgB6AIoCAI4BAIIGAJgBAJoBAJQBAIIBASgBiAEBCQaUCwCeAQCmAQCYAQCYAQCWAQB6APwBAMwBANgBAJYBAJYBAMoBAN4BAG4AzgEAsAYAegCUAgCOAQA
 
 
 ---
@@ -498,6 +511,9 @@ test 'diamond with two paths to same dep', fn:
         (local $:imp_url (ref null any))
         (local $:imp_caps_arg (ref null $rt/apply.wat:Captures))
         (local $:imp_mod_clos (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_2 10)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_2 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:caps_arg (array.new_fixed $rt/apply.wat:Captures 1 (local.get $:ret_2)))
         (local.set $:v_70 (struct.new $rt/apply.wat:Closure (ref.func $./test.fnk::v_124) (local.get $:caps_arg)))
@@ -899,6 +915,9 @@ test 'diamond with two paths to same dep', fn:
         (local $:imp_url (ref null any))
         (local $:imp_caps_arg (ref null $rt/apply.wat:Captures))
         (local $:imp_mod_clos (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_3 23)))
+        (call $rt/modules.wat:register_module (i32.const 1) (local.get $:mod_reg_url))
         (local.set $:ret_5 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_total_3 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $./test_link/diamond.fnk:total (local.get $:cell_total_3))
@@ -927,6 +946,9 @@ test 'diamond with two paths to same dep', fn:
         (local $:pub_name (ref null any))
         (local $:unwrap_base_0 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_11 26)))
+        (call $rt/modules.wat:register_module (i32.const 2) (local.get $:mod_reg_url))
         (local.set $:ret_1 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_base_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $./test_link/sub/common.fnk:base (local.get $:cell_base_0))
@@ -1087,6 +1109,9 @@ test 'diamond with two paths to same dep', fn:
         (local $:imp_url (ref null any))
         (local $:imp_caps_arg (ref null $rt/apply.wat:Captures))
         (local $:imp_mod_clos (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_13 24)))
+        (call $rt/modules.wat:register_module (i32.const 3) (local.get $:mod_reg_url))
         (local.set $:ret_3 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_left_val_1 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $./test_link/sub/left.fnk:left_val (local.get $:cell_left_val_1))
@@ -1243,6 +1268,9 @@ test 'diamond with two paths to same dep', fn:
         (local $:imp_url (ref null any))
         (local $:imp_caps_arg (ref null $rt/apply.wat:Captures))
         (local $:imp_mod_clos (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_17 25)))
+        (call $rt/modules.wat:register_module (i32.const 4) (local.get $:mod_reg_url))
         (local.set $:ret_3 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_right_val_1 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $./test_link/sub/right.fnk:right_val (local.get $:cell_right_val_1))
@@ -1288,4 +1316,4 @@ test 'diamond with two paths to same dep', fn:
       (data $d_19 "base")
       (data $d_20 "./test_link/sub/common.fnk")
     )
-    ;; sm:ugPsDwCWAQC6AQDGAQECBVgAbgDCAQCEBwCWAQCaAQCWAQC6AQDGAQBuAL4BAM4IAJYBALoBAMYBAMYBALgBANwBAQEqkgEBACrCBgC6AQDGAQBuAM4IAJoBAJoBAJoBAJoBAJQBAOABANwBALYBANwBAQAqwAQAWACwCQCUAQC6AQDGAQC4AQDeAQB6AN4BAHoA3gEAbgC8AQC-AQC-AQCqCACYAQC0AQDeAQCWAQCCAQCcAgCIBgB6APIBAI4BAKAJAJYBALoBAMYBAMoBANgBAJYBAJYBAM4BAN4BAG4A0gEArggAlgEAugEAxgEA0AEAuAEA-gEBgAkbggoAlgEAugEAxgEA0AEAzgEBqwMEVgDuAQD6AQGsAw_eBwCWAQCaAQCWAQC6AQDIAQBuAL4BAPIIAJYBALoBAMgBAMgBALoBAPoBAa0DIpIBAQAi5AYAugEAyAEAbgD0CACcAQCaAQCcAQCaAQCWAQDkAQD6AQC4AQD6AQEAIuAEAFgA8goAlgEAugEAxgEA0AEAzgEAogIA-AEAegD4AQB6APgBAG4AvgEAvgEAvgEAjgsAlgEAugEAxgEAzgEBSwlgAJ4CAPoBAJYBAIIBAKICAN4HAJYBAJoBAJYBALoBAMgBAG4AvgEA8ggAlgEAugEAyAEAyAEAugEA-gEBASaSAQEAJuQGALoBAMgBAG4A9AgAnAEAmgEAnAEAmgEAlgEA5AEA-gEAuAEA-gEBACbgBABYAKIKAJYBALoBAMYBAM4BAOwBAPoBAHoA-AEAegD6AQBuAL4BAMABAMABALoKAJYBALoBAMYBAUcIXgDoAQD6AQCWAQCCAQCgAgDeBwCWAQCaAQCWAQC6AQDIAQBuAL4BAPIIAJYBALoBAMgBAMgBALoBAPoBAQEkkgEBACTkBgC6AQDIAQBuAPQIAJwBAJoBAJwBAJoBAJYBAOQBAPoBALgBAPoBAQAk4AQAWADOCQCUAQC6AQDGAQC4AQD6AQB6APgBAHoA-gEAbgC8AQDAAQDAAQC4CQCYAQCcAQCWAQC0AQD6AQCYAQCCAQCeAgDYBgB6AIwCAI4BALIJAJgBAJoBAJgBAbkEBIoBANABANoBAJgBAJgBAMwBAOABAG4A0AEAqgYAegCSAgCQAQCqCQCWAQC6AQDEAQDSAQDmAQCYAQCYAQDUAQDsAQBuANgBAOYIAJYBALoBAMYBAe4BBFYAuAEA-AEBYgGKAQENCNQHAJYBAJoBAJYBALoBAMgBAG4AvgEA8ggAlgEAugEAyAEAyAEAugEA-gEBVR6UAQEAHuQGALoBAMgBAG4A7ggAmgEAmgEAnAEAmgEAlAEA4gEA-gEAuAEA-gEBAB7cBABYAMwJAJQBALoBAMYBALgBAPoBAHoA-gEAegD6AQBuALwBAL4BAL4BAL4JAJgBAKIBAKQBALQBAPoBAJgBAIIBAKICANwGAHoAjgIAkAEAsAkAlgEAugEAxAEA1gEA7AEAmAEAmAEA1gEA8gEAbgDaAQDoCACWAQC6AQDGAQGMAwRWALgBAPoBAW4BigEBDQjWBwCWAQCaAQCWAQC6AQDIAQBuAL4BAPQIAJYBALoBAMgBAMgBALoBAPwBAWEjlAEBACPmBgC6AQDIAQBuAPAIAJoBAJoBAJwBAJoBAJQBAOIBAPwBALgBAPwBAQAj3gQAWADOCQCUAQC6AQDGAQC4AQD8AQB6APwBAHoA_AEAbgC8AQC-AQC-AQDCCQCYAQCkAQCqAQC0AQD8AQCYAQCCAQCiAgDiBgB6AJACAJABAA
+    ;; sm:xAPsDwCWAQC6AQDGAQECBVgAbgDCAQCEBwCWAQCaAQCWAQC6AQDGAQBuAL4BAM4IAJYBALoBAMYBAMYBALgBANwBAQEqkgEBACrCBgC6AQDGAQBuAM4IAJoBAJoBAJoBAJoBAJQBAOABANwBALYBANwBAQAqwAQAWACwCQCUAQC6AQDGAQC4AQDeAQB6AN4BAHoA3gEAbgC8AQC-AQC-AQD8CACeAQCmAQCYAQC0AQDeAQCWAQCCAQCcAgCIBgB6APIBAI4BAKAJAJYBALoBAMYBAMoBANgBAJYBAJYBAM4BAN4BAG4A0gEArggAlgEAugEAxgEA0AEAuAEA-gEBgAkbggoAlgEAugEAxgEA0AEAzgEBqwMEVgDuAQD6AQGsAw_eBwCWAQCaAQCWAQC6AQDIAQBuAL4BAPIIAJYBALoBAMgBAMgBALoBAPoBAa0DIpIBAQAi5AYAugEAyAEAbgD0CACcAQCaAQCcAQCaAQCWAQDkAQD6AQC4AQD6AQEAIuAEAFgA8goAlgEAugEAxgEA0AEAzgEAogIA-AEAegD4AQB6APgBAG4AvgEAvgEAvgEAjgsAlgEAugEAxgEAzgEBSwlgAJ4CAPoBAJYBAIIBAKICAN4HAJYBAJoBAJYBALoBAMgBAG4AvgEA8ggAlgEAugEAyAEAyAEAugEA-gEBASaSAQEAJuQGALoBAMgBAG4A9AgAnAEAmgEAnAEAmgEAlgEA5AEA-gEAuAEA-gEBACbgBABYAKIKAJYBALoBAMYBAM4BAOwBAPoBAHoA-AEAegD6AQBuAL4BAMABAMABALoKAJYBALoBAMYBAUcIXgDoAQD6AQCWAQCCAQCgAgDeBwCWAQCaAQCWAQC6AQDIAQBuAL4BAPIIAJYBALoBAMgBAMgBALoBAPoBAQEkkgEBACTkBgC6AQDIAQBuAPQIAJwBAJoBAJwBAJoBAJYBAOQBAPoBALgBAPoBAQAk4AQAWADOCQCUAQC6AQDGAQC4AQD6AQB6APgBAHoA-gEAbgC8AQDAAQDAAQCKCgCeAQCmAQCYAQCcAQCWAQC0AQD6AQCYAQCCAQCeAgDYBgB6AIwCAI4BAIQKAKABAKYBAJgBAJoBAJgBAbkEBIoBANABANoBAJgBAJgBAMwBAOABAG4A0AEAqgYAegCSAgCQAQCqCQCWAQC6AQDEAQDSAQDmAQCYAQCYAQDUAQDsAQBuANgBAOYIAJYBALoBAMYBAe4BBFYAuAEA-AEBYgGKAQENCNQHAJYBAJoBAJYBALoBAMgBAG4AvgEA8ggAlgEAugEAyAEAyAEAugEA-gEBVR6UAQEAHuQGALoBAMgBAG4A7ggAmgEAmgEAnAEAmgEAlAEA4gEA-gEAuAEA-gEBAB7cBABYAMwJAJQBALoBAMYBALgBAPoBAHoA-gEAegD6AQBuALwBAL4BAL4BAJAKAKABAKYBAJgBAKIBAKQBALQBAPoBAJgBAIIBAKICANwGAHoAjgIAkAEAsAkAlgEAugEAxAEA1gEA7AEAmAEAmAEA1gEA8gEAbgDaAQDoCACWAQC6AQDGAQGMAwRWALgBAPoBAW4BigEBDQjWBwCWAQCaAQCWAQC6AQDIAQBuAL4BAPQIAJYBALoBAMgBAMgBALoBAPwBAWEjlAEBACPmBgC6AQDIAQBuAPAIAJoBAJoBAJwBAJoBAJQBAOIBAPwBALgBAPwBAQAj3gQAWADOCQCUAQC6AQDGAQC4AQD8AQB6APwBAHoA_AEAbgC8AQC-AQC-AQCUCgCgAQCmAQCYAQCkAQCqAQC0AQD8AQCYAQCCAQCiAgDiBgB6AJACAJABAA
diff --git a/src/passes/wasm/test_literals.fnk b/src/passes/wasm/test_literals.fnk
index 96c9e28..9de6a46 100644
--- a/src/passes/wasm/test_literals.fnk
+++ b/src/passes/wasm/test_literals.fnk
@@ -12,6 +12,9 @@ test 'literal bool', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (ref.i31 (i32.const 1)))
         (local.set $:args (call $rt/apply.wat:args_empty))
@@ -29,7 +32,7 @@ test 'literal bool', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CZAFAJgBAQAEYABuAMABAKYFAHoA5gEAjAEA
+    ;; sm:C-IFAJwBAKYBAJgBAQAEYABuAMABAKYFAHoA5gEAjAEA
 
 
 test 'literal bool false', fn:
@@ -42,6 +45,9 @@ test 'literal bool false', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (ref.i31 (i32.const 0)))
         (local.set $:args (call $rt/apply.wat:args_empty))
@@ -59,7 +65,7 @@ test 'literal bool false', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CZAFAJgBAQAFYABuAMABAKYFAHoA5gEAjAEA
+    ;; sm:C-IFAJwBAKYBAJgBAQAFYABuAMABAKYFAHoA5gEAjAEA
 
 
 test 'literal int', fn:
@@ -72,6 +78,9 @@ test 'literal int', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (struct.new $std/int.wat:I64 (i64.const 42)))
         (local.set $:args (call $rt/apply.wat:args_empty))
@@ -89,7 +98,7 @@ test 'literal int', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CZAFAJgBAQACigEAbgDAAQCmBQB6AOYBAIwBAA
+    ;; sm:C-IFAJwBAKYBAJgBAQACigEAbgDAAQCmBQB6AOYBAIwBAA
 
 
 test 'literal neg 0', fn:
@@ -102,6 +111,9 @@ test 'literal neg 0', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (struct.new $std/int.wat:I64 (i64.const 0)))
         (local.set $:args (call $rt/apply.wat:args_empty))
@@ -119,7 +131,7 @@ test 'literal neg 0', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CZAFAJgBAQACiAEAbgDAAQCmBQB6AOYBAIwBAA
+    ;; sm:C-IFAJwBAKYBAJgBAQACiAEAbgDAAQCmBQB6AOYBAIwBAA
 
 
 
@@ -133,6 +145,9 @@ test 'literal float', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (struct.new $std/float.wat:F64 (f64.const 123400)))
         (local.set $:args (call $rt/apply.wat:args_empty))
@@ -150,7 +165,7 @@ test 'literal float', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CZAFAJgBAQAIlgEAbgDAAQCmBQB6AOYBAIwBAA
+    ;; sm:C-IFAJwBAKYBAJgBAQAIlgEAbgDAAQCmBQB6AOYBAIwBAA
 
 
 test 'literal decimal', fn:
@@ -163,6 +178,9 @@ test 'literal decimal', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (struct.new $std/decimal.wat:Decimal (i64.const 10) (i32.const -1)))
         (local.set $:args (call $rt/apply.wat:args_empty))
@@ -180,7 +198,7 @@ test 'literal decimal', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CZAFAJgBAQAEuAEAbgDAAQCmBQB6AOYBAIwBAA
+    ;; sm:C-IFAJwBAKYBAJgBAQAEuAEAbgDAAQCmBQB6AOYBAIwBAA
 
 
 
diff --git a/src/passes/wasm/test_operators.fnk b/src/passes/wasm/test_operators.fnk
index 3cb0b6c..06e29e9 100644
--- a/src/passes/wasm/test_operators.fnk
+++ b/src/passes/wasm/test_operators.fnk
@@ -13,6 +13,9 @@ test 'add two literals', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:lit_2 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (struct.new $std/int.wat:I64 (i64.const 2)))
         (local.set $:lit_2 (struct.new $std/int.wat:I64 (i64.const 3)))
@@ -29,7 +32,7 @@ test 'add two literals', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CJwFAJgBAQABiAEBCAGIAQEHBdoFAHoA5gEAjAEA
+    ;; sm:Cu4FAJwBAKYBAJgBAQABiAEBCAGIAQEHBdoFAHoA5gEAjAEA
 
 
 
@@ -56,6 +59,9 @@ test 'chained arithmetic', fn:
         (local $:caps_arg (ref null $rt/apply.wat:Captures))
         (local $:lit_1 (ref null any))
         (local $:lit_2 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:caps_arg (array.new_fixed $rt/apply.wat:Captures 1 (local.get $:ret_0)))
         (local.set $:v_16 (struct.new $rt/apply.wat:Closure (ref.func $test::v_24) (local.get $:caps_arg)))
@@ -74,7 +80,7 @@ test 'chained arithmetic', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:D_YFAJQBALoBAMQBARABiAEBDwnGBwCYAQC0AQDQAQEAAYgBAQgBiAEBBwXWBQB6AOYBAIwBAA
+    ;; sm:EfYFAJQBALoBAMQBARABiAEBDwmYCACcAQCmAQCYAQC0AQDQAQEAAYgBAQgBiAEBBwXWBQB6AOYBAIwBAA
 
 
 test 'unary not', fn:
@@ -86,6 +92,9 @@ test 'unary not', fn:
       (func $test::fink_module (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (ref.i31 (i32.const 1)))
         (return_call $std/operators.fnk:op_not (local.get $:ctx_param) (local.get $:lit_1) (local.get $:ret_0))
@@ -101,7 +110,7 @@ test 'unary not', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:B9YEAJgBAQgEYAEHCLAFAHoA5gEAjAEA
+    ;; sm:CagFAJwBAKYBAJgBAQgEYAEHCLAFAHoA5gEAjAEA
 
 
 test 'comparison eq', fn:
@@ -114,6 +123,9 @@ test 'comparison eq', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:lit_2 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (struct.new $std/int.wat:I64 (i64.const 2)))
         (local.set $:lit_2 (struct.new $std/int.wat:I64 (i64.const 3)))
@@ -130,7 +142,7 @@ test 'comparison eq', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CJwFAJgBAQABiAEBCgGIAQEJBtYFAHoA5gEAjAEA
+    ;; sm:Cu4FAJwBAKYBAJgBAQABiAEBCgGIAQEJBtYFAHoA5gEAjAEA
 
 
 test 'comparison lt', fn:
@@ -143,6 +155,9 @@ test 'comparison lt', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:lit_2 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (struct.new $std/int.wat:I64 (i64.const 2)))
         (local.set $:lit_2 (struct.new $std/int.wat:I64 (i64.const 3)))
@@ -159,7 +174,7 @@ test 'comparison lt', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CJwFAJgBAQABiAEBCAGIAQEHBdYFAHoA5gEAjAEA
+    ;; sm:Cu4FAJwBAKYBAJgBAQABiAEBCAGIAQEHBdYFAHoA5gEAjAEA
 
 
 test 'logical and', fn:
@@ -172,6 +187,9 @@ test 'logical and', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:lit_2 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (ref.i31 (i32.const 1)))
         (local.set $:lit_2 (ref.i31 (i32.const 0)))
@@ -188,7 +206,7 @@ test 'logical and', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CJwFAJgBAQAEYAESBWABEQ7YBQB6AOYBAIwBAA
+    ;; sm:Cu4FAJwBAKYBAJgBAQAEYAESBWABEQ7YBQB6AOYBAIwBAA
 
 
 test 'logical or', fn:
@@ -201,6 +219,9 @@ test 'logical or', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:lit_2 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (ref.i31 (i32.const 1)))
         (local.set $:lit_2 (ref.i31 (i32.const 0)))
@@ -217,7 +238,7 @@ test 'logical or', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CJwFAJgBAQAEYAEQBWABDw3WBQB6AOYBAIwBAA
+    ;; sm:Cu4FAJwBAKYBAJgBAQAEYAEQBWABDw3WBQB6AOYBAIwBAA
 
 
 test 'power', fn:
@@ -230,6 +251,9 @@ test 'power', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:lit_2 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (struct.new $std/int.wat:I64 (i64.const 2)))
         (local.set $:lit_2 (struct.new $std/int.wat:I64 (i64.const 8)))
@@ -246,7 +270,7 @@ test 'power', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CJwFAJgBAQABiAEBCgGIAQEJBtgFAHoA5gEAjAEA
+    ;; sm:Cu4FAJwBAKYBAJgBAQABiAEBCgGIAQEJBtgFAHoA5gEAjAEA
 
 
 test 'power float', fn:
@@ -259,6 +283,9 @@ test 'power float', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:lit_2 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (struct.new $std/float.wat:F64 (f64.const 2)))
         (local.set $:lit_2 (struct.new $std/float.wat:F64 (f64.const 0.5)))
@@ -275,7 +302,7 @@ test 'power float', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CJwFAJgBAQADjAEBDgOQAQENCtgFAHoA5gEAjAEA
+    ;; sm:Cu4FAJwBAKYBAJgBAQADjAEBDgOQAQENCtgFAHoA5gEAjAEA
 
 
 test 'divmod', fn:
@@ -288,6 +315,9 @@ test 'divmod', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:lit_2 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (struct.new $std/int.wat:I64 (i64.const 10)))
         (local.set $:lit_2 (struct.new $std/int.wat:I64 (i64.const 3)))
@@ -304,7 +334,7 @@ test 'divmod', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CJwFAJgBAQACigEBDAGIAQELB94FAHoA5gEAjAEA
+    ;; sm:Cu4FAJwBAKYBAJgBAQACigEBDAGIAQELB94FAHoA5gEAjAEA
 
 
 test 'rotate left', fn:
@@ -317,6 +347,9 @@ test 'rotate left', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:lit_2 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (struct.new $std/int.wat:I64 (i64.const 1)))
         (local.set $:lit_2 (struct.new $std/int.wat:I64 (i64.const 4)))
@@ -333,7 +366,7 @@ test 'rotate left', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CJwFAJgBAQABiAEBDAGIAQELB9oFAHoA5gEAjAEA
+    ;; sm:Cu4FAJwBAKYBAJgBAQABiAEBDAGIAQELB9oFAHoA5gEAjAEA
 
 
 test 'rotate right', fn:
@@ -346,6 +379,9 @@ test 'rotate right', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:lit_2 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (struct.new $std/int.wat:I64 (i64.const 16)))
         (local.set $:lit_2 (struct.new $std/int.wat:I64 (i64.const 4)))
@@ -362,4 +398,4 @@ test 'rotate right', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CJwFAJgBAQACigEBDgGIAQENCNoFAHoA5gEAjAEA
+    ;; sm:Cu4FAJwBAKYBAJgBAQACigEBDgGIAQENCNoFAHoA5gEAjAEA
diff --git a/src/passes/wasm/test_range.fnk b/src/passes/wasm/test_range.fnk
index 85f8f0b..4f3490d 100644
--- a/src/passes/wasm/test_range.fnk
+++ b/src/passes/wasm/test_range.fnk
@@ -12,6 +12,9 @@ test 'range exclusive', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:lit_2 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (struct.new $std/int.wat:I64 (i64.const 0)))
         (local.set $:lit_2 (struct.new $std/int.wat:I64 (i64.const 10)))
@@ -28,7 +31,7 @@ test 'range exclusive', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CJwFAJgBAQABiAEBBgKKAQEFBcwFAHoA5gEAjAEA
+    ;; sm:Cu4FAJwBAKYBAJgBAQABiAEBBgKKAQEFBcwFAHoA5gEAjAEA
 
 
 test 'range inclusive', fn:
@@ -41,6 +44,9 @@ test 'range inclusive', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:lit_2 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (struct.new $std/int.wat:I64 (i64.const 0)))
         (local.set $:lit_2 (struct.new $std/int.wat:I64 (i64.const 10)))
@@ -57,7 +63,7 @@ test 'range inclusive', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CJwFAJgBAQABiAEBCAKKAQEHBswFAHoA5gEAjAEA
+    ;; sm:Cu4FAJwBAKYBAJgBAQABiAEBCAKKAQEHBswFAHoA5gEAjAEA
 
 
 test 'open range exclusive', fn:
@@ -69,6 +75,9 @@ test 'open range exclusive', fn:
       (func $test::fink_module (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (struct.new $std/int.wat:I64 (i64.const 0)))
         (return_call $std/range.fnk:from (local.get $:ctx_param) (local.get $:lit_1) (local.get $:ret_0))
@@ -84,7 +93,7 @@ test 'open range exclusive', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:B9YEAJgBAQABiAEBAAOkBQB6AOYBAIwBAA
+    ;; sm:CagFAJwBAKYBAJgBAQABiAEBAAOkBQB6AOYBAIwBAA
 
 
 test 'range in', fn:
@@ -110,6 +119,9 @@ test 'range in', fn:
         (local $:caps_arg (ref null $rt/apply.wat:Captures))
         (local $:lit_2 (ref null any))
         (local $:lit_3 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:caps_arg (array.new_fixed $rt/apply.wat:Captures 1 (local.get $:ret_0)))
         (local.set $:v_16 (struct.new $rt/apply.wat:Closure (ref.func $test::v_24) (local.get $:caps_arg)))
@@ -128,4 +140,4 @@ test 'range in', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:D_YFAJQBALoBAMQBAQABiAEBAArCBwCYAQC0AQDQAQEKAYgBAQYCigEBBQXKBQB6AOYBAIwBAA
+    ;; sm:EfYFAJQBALoBAMQBAQABiAEBAAqUCACcAQCmAQCYAQC0AQDQAQEKAYgBAQYCigEBBQXKBQB6AOYBAIwBAA
diff --git a/src/passes/wasm/test_records.fnk b/src/passes/wasm/test_records.fnk
index 71fb74b..158cd8b 100644
--- a/src/passes/wasm/test_records.fnk
+++ b/src/passes/wasm/test_records.fnk
@@ -29,6 +29,9 @@ test 'rec literal', fn:
         (local $:lit_1 (ref null any))
         (local $:lit_2 (ref null any))
         (local $:lit_3 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_2 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:caps_arg (array.new_fixed $rt/apply.wat:Captures 1 (local.get $:ret_0)))
         (local.set $:v_18 (struct.new $rt/apply.wat:Closure (ref.func $test::v_26) (local.get $:caps_arg)))
@@ -50,7 +53,7 @@ test 'rec literal', fn:
       (data $d_1 "a")
       (data $d_2 "test")
     )
-    ;; sm:Eb4HAJQBALoBAMQBAQ4BkAEBBgGIAQEFBKAIAJgBALQBANABAQ0MYAECAZABAQYBiAEBBQTsBQB6AOYBAIwBAA
+    ;; sm:E74HAJQBALoBAMQBAQ4BkAEBBgGIAQEFBPIIAJwBAKYBAJgBALQBANABAQ0MYAECAZABAQYBiAEBBQTsBQB6AOYBAIwBAA
 
 
 test 'rec destructure', fn:
@@ -216,6 +219,9 @@ test 'rec destructure', fn:
         (local $:lit_3 (ref null any))
         (local $:lit_4 (ref null any))
         (local $:lit_5 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_2 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_2 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_a_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test::a_0 (local.get $:cell_a_0))
@@ -240,7 +246,7 @@ test 'rec destructure', fn:
       (data $d_1 "a")
       (data $d_2 "test")
     )
-    ;; sm:WIwIAJYBAJoBAJYBALoBAMYBAKIBAQ4BUACuAQEkBfoHAJYBAJoBAJYBALoBAMgBAMIBAG4AvgEAwAEAjgkAlgEAmgEAlgEAugEAyAEAyAEA4AEA0gEBMRiSAQEAGJAJAJYBALoBAMgBAMgBAOgBANIBAQAYkgEBABi8BgC6AQDIAQBuAMoIAJwBAJoBAJwBAJoBAJYBAOQBANIBALgBANIBAQAYtgQAWACmCQCWAQC6AQDGAQC4AQDSAQB6ANIBAHoA0gEAbgC-AQC-AQC-AQC2CACUAQC6AQDGAQC4AQDSAQEmAZABAQYBiAEBBQSICQCYAQCUAQBmALQBANQBAQ0MYAECAZABAQYBiAEBBQTuBQB6AOYBAIwBAA
+    ;; sm:WowIAJYBAJoBAJYBALoBAMYBAKIBAQ4BUACuAQEkBfoHAJYBAJoBAJYBALoBAMgBAMIBAG4AvgEAwAEAjgkAlgEAmgEAlgEAugEAyAEAyAEA4AEA0gEBMRiSAQEAGJAJAJYBALoBAMgBAMgBAOgBANIBAQAYkgEBABi8BgC6AQDIAQBuAMoIAJwBAJoBAJwBAJoBAJYBAOQBANIBALgBANIBAQAYtgQAWACmCQCWAQC6AQDGAQC4AQDSAQB6ANIBAHoA0gEAbgC-AQC-AQC-AQC2CACUAQC6AQDGAQC4AQDSAQEmAZABAQYBiAEBBQTaCQCcAQCmAQCYAQCUAQBmALQBANQBAQ0MYAECAZABAQYBiAEBBQTuBQB6AOYBAIwBAA
 
 test 'rec spread', fn:
   expect wat ƒink:
@@ -321,6 +327,9 @@ test 'rec spread', fn:
         (local $:lit_2 (ref null any))
         (local $:lit_3 (ref null any))
         (local $:lit_4 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_1 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_1 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_r_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:r (local.get $:cell_r_0))
@@ -349,7 +358,7 @@ test 'rec spread', fn:
       (data $d_3 "b")
       (data $d_4 "a")
     )
-    ;; sm:LMQHAJYBALoBAMQBAS4BkgEBBgGKAQEFBKgMAJQBALoBAM4BALoBAMQBAJwBAKIBAJQBAJYBAMYBALYBANABAQsLYgCsAQECA54KAJQBALoBAM4BALoBAMQBAOIBANABAQ0BkAEBBgGIAQEFBIYJAJgBAJQBAGAA3gEA0AEBDQxgAQIBkAEBBgGIAQEFBOwFAHoA5gEAjAEA
+    ;; sm:LsQHAJYBALoBAMQBAS4BkgEBBgGKAQEFBKgMAJQBALoBAM4BALoBAMQBAJwBAKIBAJQBAJYBAMYBALYBANABAQsLYgCsAQECA54KAJQBALoBAM4BALoBAMQBAOIBANABAQ0BkAEBBgGIAQEFBNgJAJwBAKYBAJgBAJQBAGAA3gEA0AEBDQxgAQIBkAEBBgGIAQEFBOwFAHoA5gEAjAEA
 
 test 'rec empty literal', fn:
   expect wat ƒink:
@@ -362,6 +371,9 @@ test 'rec empty literal', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (call $std/rec.fnk:new))
         (local.set $:args (call $rt/apply.wat:args_empty))
@@ -379,7 +391,7 @@ test 'rec empty literal', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CZIGAJgBAQACYABuAMABAKYFAHoA5gEAjAEA
+    ;; sm:C-QGAJwBAKYBAJgBAQACYABuAMABAKYFAHoA5gEAjAEA
 
 test 'rec single field', fn:
   expect wat ƒink:
@@ -393,6 +405,9 @@ test 'rec single field', fn:
         (local $:lit_1 (ref null any))
         (local $:lit_2 (ref null any))
         (local $:lit_3 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_1 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (call $std/rec.fnk:new))
         (local.set $:lit_2 (call $std/str.fnk:from_data (data.ref $d_0 1)))
@@ -411,7 +426,7 @@ test 'rec single field', fn:
       (data $d_0 "a")
       (data $d_1 "test")
     )
-    ;; sm:CeQGAJgBAQAGYAECAZABAQYBiAEBBQTuBQB6AOYBAIwBAA
+    ;; sm:C7YHAJwBAKYBAJgBAQAGYAECAZABAQYBiAEBBQTuBQB6AOYBAIwBAA
 
 test 'rec nested destructure', fn:
   expect wat ƒink:
@@ -646,6 +661,9 @@ test 'rec nested destructure', fn:
         (local $:lit_5 (ref null any))
         (local $:lit_6 (ref null any))
         (local $:lit_7 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_2 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_2 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_a_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test::a_0 (local.get $:cell_a_0))
@@ -673,7 +691,7 @@ test 'rec nested destructure', fn:
       (data $d_1 "a")
       (data $d_2 "test")
     )
-    ;; sm:fcIHAJYBALoBAMYBAKIBAK4BAG4AygEA_AYAlgEAmgEAlgEAugEAyAEAbgC-AQDMCACWAQC6AQDIAQDIAQC6AQDUAQEmB5IBAQAHvgYAugEAyAEAbgDOCACcAQCaAQCcAQCaAQCWAQDkAQDUAQC4AQDUAQEAB7oEAFgA9gkAlgEAugEAxgEAogEAuAEA0gEAegDSAQB6ANIBAK4BAG4AygEAvgEAvgEA9gYAlgEAmgEAlgEAugEAyAEAbgC-AQDMCACWAQC6AQDIAQDIAQC6AQDUAQElEpIBAQASvgYAugEAyAEAbgDOCACcAQCaAQCcAQCaAQCWAQDkAQDUAQC4AQDUAQEAEroEAFgApgkAlgEAugEAxgEAuAEA0gEAegDSAQB6ANIBAG4AvgEAvgEAvgEAuAgAlAEAugEAxgEAuAEA1AEBDAxgAQIBkAEBAAr0CQCYAQCUAQBmAJQBAGYAtAEA1AEBBgdgAQIBkAEBBgKKAQEFBe4FAHoA5gEAjAEA
+    ;; sm:f8IHAJYBALoBAMYBAKIBAK4BAG4AygEA_AYAlgEAmgEAlgEAugEAyAEAbgC-AQDMCACWAQC6AQDIAQDIAQC6AQDUAQEmB5IBAQAHvgYAugEAyAEAbgDOCACcAQCaAQCcAQCaAQCWAQDkAQDUAQC4AQDUAQEAB7oEAFgA9gkAlgEAugEAxgEAogEAuAEA0gEAegDSAQB6ANIBAK4BAG4AygEAvgEAvgEA9gYAlgEAmgEAlgEAugEAyAEAbgC-AQDMCACWAQC6AQDIAQDIAQC6AQDUAQElEpIBAQASvgYAugEAyAEAbgDOCACcAQCaAQCcAQCaAQCWAQDkAQDUAQC4AQDUAQEAEroEAFgApgkAlgEAugEAxgEAuAEA0gEAegDSAQB6ANIBAG4AvgEAvgEAvgEAuAgAlAEAugEAxgEAuAEA1AEBDAxgAQIBkAEBAArGCgCcAQCmAQCYAQCUAQBmAJQBAGYAtAEA1AEBBgdgAQIBkAEBBgKKAQEFBe4FAHoA5gEAjAEA
 
 test 'rec spread merge two', fn:
   expect wat ƒink:
@@ -776,6 +794,9 @@ test 'rec spread merge two', fn:
         (local $:lit_3 (ref null any))
         (local $:lit_4 (ref null any))
         (local $:lit_5 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_2 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_r1_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:r1 (local.get $:cell_r1_0))
@@ -810,7 +831,7 @@ test 'rec spread merge two', fn:
       (data $d_3 "b")
       (data $d_4 "a")
     )
-    ;; sm:OcIIAJYBALoBAM4BALoBAMQBAK4BAT4Ezg0AlgEAugEAzgEAugEAxAEAzgEAugEAngEApgEAlAEAlgEAyAEA4gEA0AEBDQxiAK4BAQIEhA4AlAEAugEAzgEAugEAzgEAugEAxAEAnAEApgEAlAEAlgEAyAEAjgIA0AEBDwZgAQIBkAEBBgGKAQEFBPoJAJgBAJYBAGQAlgEAZACMAgDQAQEZBmABAgGQAQEGAYgBAQUE7AUAegDmAQCMAQA
+    ;; sm:O8IIAJYBALoBAM4BALoBAMQBAK4BAT4Ezg0AlgEAugEAzgEAugEAxAEAzgEAugEAngEApgEAlAEAlgEAyAEA4gEA0AEBDQxiAK4BAQIEhA4AlAEAugEAzgEAugEAzgEAugEAxAEAnAEApgEAlAEAlgEAyAEAjgIA0AEBDwZgAQIBkAEBBgGKAQEFBMwKAJwBAKYBAJgBAJYBAGQAlgEAZACMAgDQAQEZBmABAgGQAQEGAYgBAQUE7AUAegDmAQCMAQA
 
 # TODO: should this be in strings?
 test 'rec format template', fn:
@@ -840,6 +861,9 @@ test 'rec format template', fn:
         (local $:lit_2 (ref null any))
         (local $:lit_3 (ref null any))
         (local $:lit_4 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_2 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:caps_arg (array.new_fixed $rt/apply.wat:Captures 1 (local.get $:ret_0)))
         (local.set $:v_17 (struct.new $rt/apply.wat:Closure (ref.func $test::v_25) (local.get $:caps_arg)))
@@ -861,7 +885,7 @@ test 'rec format template', fn:
       (data $d_1 "a")
       (data $d_2 "test")
     )
-    ;; sm:EeYHAJQBALoBAMQBAQIFkAEA1AEBARDmBwCYAQC0AQDQAQEQBmABAgGQAQEGAYgBAQUE7AUAegDmAQCMAQA
+    ;; sm:E-YHAJQBALoBAMQBAQIFkAEA1AEBARC4CACcAQCmAQCYAQC0AQDQAQEQBmABAgGQAQEGAYgBAQUE7AUAegDmAQCMAQA
 
 test 'rec dot dynamic key', fn:
   expect wat ƒink:
@@ -920,6 +944,9 @@ test 'rec dot dynamic key', fn:
         (local $:lit_3 (ref null any))
         (local $:lit_4 (ref null any))
         (local $:lit_5 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_2 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_r_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:r (local.get $:cell_r_0))
@@ -950,5 +977,5 @@ test 'rec dot dynamic key', fn:
       (data $d_2 "a")
       (data $d_3 "k")
     )
-    ;; sm:JMwOAJQBALoBAM4BALoBAM4BALoBAMQBAJwBAKIBAJQBAJYBAMYBARgBjAEAnAEAogEAlAEAlgEAxgEArAEArAEBEAX6CQCYAQCUAQBgAJQBAGAAiAIA0AEBHwdgAQIBkAEBBgKKAQEFBewFAHoA5gEAjAEA
-BAK4BAMwBAR8HWgECAYoBAQYChAEBBQXYBQB6AOYBAIwBAA
+    ;; sm:JswOAJQBALoBAM4BALoBAM4BALoBAMQBAJwBAKIBAJQBAJYBAMYBARgBjAEAnAEAogEAlAEAlgEAxgEArAEArAEBEAXMCgCcAQCmAQCYAQCUAQBgAJQBAGAAiAIA0AEBHwdgAQIBkAEBBgKKAQEFBewFAHoA5gEAjAEA
+
diff --git a/src/passes/wasm/test_sets.fnk b/src/passes/wasm/test_sets.fnk
index 526618c..440355b 100644
--- a/src/passes/wasm/test_sets.fnk
+++ b/src/passes/wasm/test_sets.fnk
@@ -33,6 +33,7 @@ test 'set import + construction', fn:
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_29) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_28) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_116) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 33))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $set_0))
       )
       (func $test::v_83 (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -134,6 +135,9 @@ test 'set import + construction', fn:
         (local $:imp_val_set (ref null any))
         (local $:imp_key_set (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_1 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_2 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:caps_arg (array.new_fixed $rt/apply.wat:Captures 1 (local.get $:ret_2)))
         (local.set $:v_75 (struct.new $rt/apply.wat:Closure (ref.func $test::v_129) (local.get $:caps_arg)))
@@ -157,7 +161,7 @@ test 'set import + construction', fn:
       (data $d_0 "set")
       (data $d_1 "test")
     )
-    ;; sm:SY4JAJYBALoBAMYBAQIDVAFAAYoBAQYBigEBBgGKAQBuAMIBAMIBAMIBAMQBAPIGAJYBAJoBAJYBALoBAMYBAG4AvgEAxAgAlgEAugEAxgEAxgEAuAEA0AEBTRySAQEAHLYGALoBAMYBAG4AwggAmgEAmgEAmgEAmgEAlAEA4AEA0gEAtgEA0AEBABy0BABYAKQJAJQBALoBAMYBALgBANIBAHoA0gEAegDSAQBuALwBAL4BAL4BANwJAJgBALQBANIBAGQAbACcAQCGAgBuAMQBAKQFAHoA5gEAjAEA
+    ;; sm:TI4JAJYBALoBAMYBAQIDVAFAAYoBAQYBigEBBgGKAQBuAMIBAMIBAMIBAMQBAIIBAPIGAJYBAJoBAJYBALoBAMYBAG4AvgEAxAgAlgEAugEAxgEAxgEAuAEA0AEBTRySAQEAHLYGALoBAMYBAG4AwggAmgEAmgEAmgEAmgEAlAEA4AEA0gEAtgEA0AEBABy0BABYAKQJAJQBALoBAMYBALgBANIBAHoA0gEAegDSAQBuALwBAL4BAL4BAK4KAJwBAKYBAJgBALQBANIBAGQAbACcAQCGAgBuAMQBAKQFAHoA5gEAjAEA
 
 
 test 'set spread', fn:
@@ -181,6 +185,7 @@ test 'set spread', fn:
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_concat (local.get $:v_36) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_107) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 40))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $set_106))
       )
       (func $test::v_123 (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -335,6 +340,9 @@ test 'set spread', fn:
         (local $:imp_val_set (ref null any))
         (local $:imp_key_set (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_1 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_2 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:caps_arg (array.new_fixed $rt/apply.wat:Captures 1 (local.get $:ret_2)))
         (local.set $:v_103 (struct.new $rt/apply.wat:Closure (ref.func $test::v_187) (local.get $:caps_arg)))
@@ -358,7 +366,7 @@ test 'set spread', fn:
       (data $d_0 "set")
       (data $d_1 "test")
     )
-    ;; sm:XboHAJYBALoBAMQBAMYBAG4AvAEAxAEAwAgAlgEAugEAxAEAxgEA4gEA0gEBSAGKAQEAAeQIAJYBALoBAMQBAMYBAOIBANIBAQYBigEBAAGoCQCWAQC6AQDGAQFLA1QA3gEA0gEBUgGKAQENCXIBDgGiBwCWAQCaAQCWAQC6AQDIAQBuAL4BAMoIAJYBALoBAMgBAMgBALoBANIBAVMckgEBABy8BgC6AQDIAQBuAMQIAJoBAJoBAJoBAJoBAJQBAOABANIBALYBANIBAQActAQAWACkCQCUAQC6AQDGAQC4AQDSAQB6ANIBAHoA0gEAbgC8AQC-AQC-AQDeCQCYAQC0AQDUAQBkAGwAnAEAhgIAbgDEAQCmBQB6AOYBAIwBAA
+    ;; sm:YLoHAJYBALoBAMQBAMYBAG4AvAEAxAEAggEAwAgAlgEAugEAxAEAxgEA4gEA0gEBSAGKAQEAAeQIAJYBALoBAMQBAMYBAOIBANIBAQYBigEBAAGoCQCWAQC6AQDGAQFLA1QA3gEA0gEBUgGKAQENCXIBDgGiBwCWAQCaAQCWAQC6AQDIAQBuAL4BAMoIAJYBALoBAMgBAMgBALoBANIBAVMckgEBABy8BgC6AQDIAQBuAMQIAJoBAJoBAJoBAJoBAJQBAOABANIBALYBANIBAQActAQAWACkCQCUAQC6AQDGAQC4AQDSAQB6ANIBAHoA0gEAbgC8AQC-AQC-AQCwCgCcAQCmAQCYAQC0AQDUAQBkAGwAnAEAhgIAbgDEAQCmBQB6AOYBAIwBAA
 
 
 test 'set destructure empty', fn:
@@ -628,6 +636,7 @@ test 'set destructure empty', fn:
         (local.set $:v_198 (struct.new $rt/apply.wat:Closure (ref.func $test::v_318) (local.get $:caps_arg)))
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:v_198) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 118))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $set_0))
       )
       (func $test::v_326 (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -730,6 +739,9 @@ test 'set destructure empty', fn:
         (local $:imp_val_set (ref null any))
         (local $:imp_key_set (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_3 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_s_1 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:s (local.get $:cell_s_1))
@@ -757,7 +769,7 @@ test 'set destructure empty', fn:
       (data $d_1 "s")
       (data $d_2 "set")
     )
-    ;; sm:vwGKBgCaAQFsAYoBAG4AwgEAuAYAugEAwgEAyAEAbgDGAQCyCACWAQC6AQDIAQDIAQCGAQB8ALINAJYBALoBAMgBAMgBAQcCVADoAQDUAQEAAvwFALoBAMgBAG4AzggAnAEAmgEAnAEAmgEAlgEA5AEA1AEAuAEA1AEBAALoCgCcAQCaAQCcAQCaAQCWAQC6AQDCAQDgAQDSAQB6ANIBAG4AvgEAxAEAvgEAyAUAmgEBFgGKAQBuAMIBAMQHAJwBAJoBAJwBAJoBAJYBALoBAMIBAG4AxAEAgAQAWACEBwC6AQDCAQDGAQDCAQB6ANQBAG4AwAEAwAEAxAEA9AgAmgEAmgEAlgEAugEAwgEAwgEAhAIA1AEAbgC-AQDAAQDCAQDyDwCWAQC6AQDGAQCcAQCiAQCUAQCWAQDGAQB6ANIBALIBANIBAHoA0gEAsgEA0gEA2AEA1AEAqAEAbgDKAQDEAQCuCACWAQC6AQDGAQF3A1QAuAEA1AEAbgDAAQD2BgCWAQCaAQCWAQC6AQDIAQBuAL4BAMwIAJYBALoBAMgBAMgBALoBANQBAQEckgEBABy-BgC6AQDIAQBuAMoIAJoBAJoBAJwBAJoBAJQBAOIBANQBALgBANQBAQAcuAQAWACoCQCUAQC6AQDGAQC4AQDUAQB6ANIBAHoA1AEAbgC8AQDAAQDAAQDICgCYAQCUAQBgALQBANQBAGQAbACcAQCGAgBuAMQBAKYFAHoA5gEAjAEA
+    ;; sm:wgGKBgCaAQFsAYoBAG4AwgEAuAYAugEAwgEAyAEAbgDGAQCyCACWAQC6AQDIAQDIAQCGAQB8ALINAJYBALoBAMgBAMgBAQcCVADoAQDUAQEAAvwFALoBAMgBAG4AzggAnAEAmgEAnAEAmgEAlgEA5AEA1AEAuAEA1AEBAALoCgCcAQCaAQCcAQCaAQCWAQC6AQDCAQDgAQDSAQB6ANIBAG4AvgEAxAEAvgEAyAUAmgEBFgGKAQBuAMIBAMQHAJwBAJoBAJwBAJoBAJYBALoBAMIBAG4AxAEAgAQAWACEBwC6AQDCAQDGAQDCAQB6ANQBAG4AwAEAwAEAxAEA9AgAmgEAmgEAlgEAugEAwgEAwgEAhAIA1AEAbgC-AQDAAQDCAQDyDwCWAQC6AQDGAQCcAQCiAQCUAQCWAQDGAQB6ANIBALIBANIBAHoA0gEAsgEA0gEA2AEA1AEAqAEAbgDKAQDEAQCuCACWAQC6AQDGAQF3A1QAuAEA1AEAbgDAAQCEAQD2BgCWAQCaAQCWAQC6AQDIAQBuAL4BAMwIAJYBALoBAMgBAMgBALoBANQBAQEckgEBABy-BgC6AQDIAQBuAMoIAJoBAJoBAJwBAJoBAJQBAOIBANQBALgBANQBAQAcuAQAWACoCQCUAQC6AQDGAQC4AQDUAQB6ANIBAHoA1AEAbgC8AQDAAQDAAQCaCwCcAQCmAQCYAQCUAQBgALQBANQBAGQAbACcAQCGAgBuAMQBAKYFAHoA5gEAjAEA
 
 
 test 'set destructure non-empty', fn:
@@ -1036,6 +1048,7 @@ test 'set destructure non-empty', fn:
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_30) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_29) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:v_201) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 121))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $set_0))
       )
       (func $test::v_329 (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -1138,6 +1151,9 @@ test 'set destructure non-empty', fn:
         (local $:imp_val_set (ref null any))
         (local $:imp_key_set (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_3 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_s_1 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:s (local.get $:cell_s_1))
@@ -1165,7 +1181,7 @@ test 'set destructure non-empty', fn:
       (data $d_1 "s")
       (data $d_2 "set")
     )
-    ;; sm:xQGKBgCaAQF4AYoBAG4AwgEAuAYAugEAwgEAyAEAbgDGAQCyCACWAQC6AQDIAQDIAQCGAQB8ALINAJYBALoBAMgBAMgBAQcCVADoAQDUAQEAAvwFALoBAMgBAG4AzggAnAEAmgEAnAEAmgEAlgEA5AEA1AEAuAEA1AEBAALoCgCcAQCaAQCcAQCaAQCWAQC6AQDCAQDgAQDSAQB6ANIBAG4AvgEAxAEAvgEAyAUAmgEBFgGKAQBuAMIBAMQHAJwBAJoBAJwBAJoBAJYBALoBAMIBAG4AxAEAgAQAWACEBwC6AQDCAQDGAQDCAQB6ANQBAG4AwAEAwAEAxAEA9AgAmgEAmgEAlgEAugEAwgEAwgEAhAIA1AEAbgC-AQDAAQDCAQDyDwCWAQC6AQDGAQCcAQCiAQCUAQCWAQDGAQB6ANIBALIBANIBAHoA0gEAsgEA0gEA2AEA1AEAqAEAbgDKAQDEAQCGCgCWAQC6AQDGAQGDAQNUALgBANQBAUgBigEBBgGKAQEGAYoBAG4AwgEAwgEAwgEAwAEA9gYAlgEAmgEAlgEAugEAyAEAbgC-AQDMCACWAQC6AQDIAQDIAQC6AQDUAQFVHJIBAQAcvgYAugEAyAEAbgDKCACaAQCaAQCcAQCaAQCUAQDiAQDUAQC4AQDUAQEAHLgEAFgAqAkAlAEAugEAxgEAuAEA1AEAegDSAQB6ANQBAG4AvAEAwAEAwAEAyAoAmAEAlAEAYAC0AQDUAQBkAGwAnAEAhgIAbgDEAQCmBQB6AOYBAIwBAA
+    ;; sm:yAGKBgCaAQF4AYoBAG4AwgEAuAYAugEAwgEAyAEAbgDGAQCyCACWAQC6AQDIAQDIAQCGAQB8ALINAJYBALoBAMgBAMgBAQcCVADoAQDUAQEAAvwFALoBAMgBAG4AzggAnAEAmgEAnAEAmgEAlgEA5AEA1AEAuAEA1AEBAALoCgCcAQCaAQCcAQCaAQCWAQC6AQDCAQDgAQDSAQB6ANIBAG4AvgEAxAEAvgEAyAUAmgEBFgGKAQBuAMIBAMQHAJwBAJoBAJwBAJoBAJYBALoBAMIBAG4AxAEAgAQAWACEBwC6AQDCAQDGAQDCAQB6ANQBAG4AwAEAwAEAxAEA9AgAmgEAmgEAlgEAugEAwgEAwgEAhAIA1AEAbgC-AQDAAQDCAQDyDwCWAQC6AQDGAQCcAQCiAQCUAQCWAQDGAQB6ANIBALIBANIBAHoA0gEAsgEA0gEA2AEA1AEAqAEAbgDKAQDEAQCGCgCWAQC6AQDGAQGDAQNUALgBANQBAUgBigEBBgGKAQEGAYoBAG4AwgEAwgEAwgEAwAEAhAEA9gYAlgEAmgEAlgEAugEAyAEAbgC-AQDMCACWAQC6AQDIAQDIAQC6AQDUAQFVHJIBAQAcvgYAugEAyAEAbgDKCACaAQCaAQCcAQCaAQCUAQDiAQDUAQC4AQDUAQEAHLgEAFgAqAkAlAEAugEAxgEAuAEA1AEAegDSAQB6ANQBAG4AvAEAwAEAwAEAmgsAnAEApgEAmAEAlAEAYAC0AQDUAQBkAGwAnAEAhgIAbgDEAQCmBQB6AOYBAIwBAA
 
 
 test 'set destructure peel one', fn:
@@ -1529,6 +1545,7 @@ test 'set destructure peel one', fn:
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_31) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:lit_30) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:v_252) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 153))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $set_0))
       )
       (func $test::v_422 (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -1631,6 +1648,9 @@ test 'set destructure peel one', fn:
         (local $:imp_val_set (ref null any))
         (local $:imp_key_set (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_4 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_s_1 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:s (local.get $:cell_s_1))
@@ -1658,5 +1678,5 @@ test 'set destructure peel one', fn:
       (data $d_1 "s")
       (data $d_2 "set")
     )
-    ;; sm:8QGKBgCaAQF4AYoBAG4AwgEAuAYAugEAwgEAyAEAbgDGAQCyCACWAQC6AQDIAQDIAQCGAQB8ALINAJYBALoBAMgBAMgBAQcCVADoAQDUAQEAAvwFALoBAMgBAG4AzggAnAEAmgEAnAEAmgEAlgEA5AEA1AEAuAEA1AEBAALoCgCcAQCaAQCcAQCaAQCWAQC6AQDCAQDgAQDSAQB6ANIBAG4AvgEAxAEAvgEA0gUAnAEAmgEAkgEBKgOQAQEHB_AHAJYBALoBAMIBAMgBAQ8BUABuAL4BAMYBAPgGAJYBAJoBAJYBALoBAMgBAG4AvgEAhAgAlgEAugEAyAEAyAEAugEA1AEBAQeUBgC6AQDIAQBuAM4IAJwBAJoBAJwBAJoBAJYBAOQBANQBALgBANQBAQAH6goAnAEAmgEAnAEAmgEAlgEAugEAwgEA4AEA1AEAegDSAQBuAL4BAMQBAMABAP4DAFgAhAcAugEAwgEAxgEAwgEAegDUAQBuAMABAMABAMQBAPgIAJwBAJoBAJgBALoBAMIBAMIBAIgCANQBAG4AwAEAwAEAxAEA9g8AlgEAugEAxgEAnAEAogEAlAEAlgEAxgEAegDSAQCyAQDSAQB6ANQBALQBANQBANoBANQBAKgBAG4AygEAxAEAhgoAlgEAugEAxgEBfQNUALgBANQBAUgBigEBBgGKAQEGAYoBAG4AwgEAwgEAwgEAwAEA9gYAlgEAmgEAlgEAugEAyAEAbgC-AQDMCACWAQC6AQDIAQDIAQC6AQDUAQFVHJIBAQAcvgYAugEAyAEAbgDMCACcAQCaAQCcAQCaAQCUAQDkAQDUAQC4AQDUAQEAHLgEAFgAqAkAlAEAugEAxgEAuAEA1AEAegDSAQB6ANQBAG4AvAEAwAEAwAEAyAoAmAEAlAEAYAC0AQDUAQBkAGwAnAEAhgIAbgDEAQCmBQB6AOYBAIwBAA
+    ;; sm:9AGKBgCaAQF4AYoBAG4AwgEAuAYAugEAwgEAyAEAbgDGAQCyCACWAQC6AQDIAQDIAQCGAQB8ALINAJYBALoBAMgBAMgBAQcCVADoAQDUAQEAAvwFALoBAMgBAG4AzggAnAEAmgEAnAEAmgEAlgEA5AEA1AEAuAEA1AEBAALoCgCcAQCaAQCcAQCaAQCWAQC6AQDCAQDgAQDSAQB6ANIBAG4AvgEAxAEAvgEA0gUAnAEAmgEAkgEBKgOQAQEHB_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-AQDMCACWAQC6AQDIAQDIAQC6AQDUAQFVHJIBAQAcvgYAugEAyAEAbgDMCACcAQCaAQCcAQCaAQCUAQDkAQDUAQC4AQDUAQEAHLgEAFgAqAkAlAEAugEAxgEAuAEA1AEAegDSAQB6ANQBAG4AvAEAwAEAwAEAmgsAnAEApgEAmAEAlAEAYAC0AQDUAQBkAGwAnAEAhgIAbgDEAQCmBQB6AOYBAIwBAA
 
diff --git a/src/passes/wasm/test_strings.fnk b/src/passes/wasm/test_strings.fnk
index 80373d4..48d6ad4 100644
--- a/src/passes/wasm/test_strings.fnk
+++ b/src/passes/wasm/test_strings.fnk
@@ -12,6 +12,9 @@ test 'empty string literal', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (call $std/str.fnk:str_empty))
         (local.set $:args (call $rt/apply.wat:args_empty))
@@ -29,7 +32,7 @@ test 'empty string literal', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CZAFAJgBAQACbABuAMABAKYFAHoA5gEAjAEA
+    ;; sm:C-IFAJwBAKYBAJgBAQACbABuAMABAKYFAHoA5gEAjAEA
 
 
 
@@ -43,6 +46,9 @@ test 'string literal', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_1 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (call $std/str.fnk:from_data (data.ref $d_0 5)))
         (local.set $:args (call $rt/apply.wat:args_empty))
@@ -61,7 +67,7 @@ test 'string literal', fn:
       (data $d_0 "hello")
       (data $d_1 "test")
     )
-    ;; sm:CZAFAJgBAQAHkAEAbgDAAQCmBQB6AOYBAIwBAA
+    ;; sm:C-IFAJwBAKYBAJgBAQAHkAEAbgDAAQCmBQB6AOYBAIwBAA
 
 
 test 'string literal dedup', fn:
@@ -85,6 +91,9 @@ test 'string literal dedup', fn:
         (local $:pub_name (ref null any))
         (local $:unwrap_y_1 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_1 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_2 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_x_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:x (local.get $:cell_x_0))
@@ -123,7 +132,7 @@ test 'string literal dedup', fn:
       (data $d_2 "x")
       (data $d_3 "y")
     )
-    ;; sm:Ga4LAJgBAJQBAGAAlAEAYAEAAYoBAJgBAKIBAJQBAJYBAMYBARgBigEAmAEAogEAlAEAlgEAxgEAqAEAbgDKAQCmBQB6AOYBAIwBAA
+    ;; sm:G4AMAJwBAKYBAJgBAJQBAGAAlAEAYAEAAYoBAJgBAKIBAJQBAJYBAMYBARgBigEAmAEAogEAlAEAlgEAxgEAqAEAbgDKAQCmBQB6AOYBAIwBAA
 
 
 test 'str templ two exprs', fn:
@@ -150,6 +159,9 @@ test 'str templ two exprs', fn:
         (local $:lit_6 (ref null any))
         (local $:unwrap_b_1 (ref null any))
         (local $:varargs (ref null $rt/apply.wat:VarArgs))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_2 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_a_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:a (local.get $:cell_a_0))
@@ -189,7 +201,7 @@ test 'str templ two exprs', fn:
       (data $d_2 "b")
       (data $d_3 " and ")
     )
-    ;; sm:GvgMAJgBAJQBAGAAlAEAYAEAAYIBAJgBAKIBAJQBAJYBAMYBAQwBggEAmAEAogEAlAEAlgEAxgEAqAEBFgWQAQCoAQCUAgEJD7AFAHoA5gEAjAEA
+    ;; sm:HMoNAJwBAKYBAJgBAJQBAGAAlAEAYAEAAYIBAJgBAKIBAJQBAJYBAMYBAQwBggEAmAEAogEAlAEAlgEAxgEAqAEBFgWQAQCoAQCUAgEJD7AFAHoA5gEAjAEA
 
 
 test 'str tagged template', fn:
@@ -206,6 +218,8 @@ test 'str tagged template', fn:
         (local.set $:ret_4 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $parts_1 (local.get $:params))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 51))
+        (call $rt/trace.wat:trace_pop (i32.const 0) (i32.const 51))
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $parts_1) (local.get $:args)))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:ret_4))
@@ -227,6 +241,7 @@ test 'str tagged template', fn:
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_concat (local.get $:v_12) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_39) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 16))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_foo_38))
       )
       (func $test::fink_module (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -241,6 +256,9 @@ test 'str tagged template', fn:
         (local $:caps_arg (ref null $rt/apply.wat:Captures))
         (local $:lit_11 (ref null any))
         (local $:lit_10 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_2 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_foo_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:foo (local.get $:cell_foo_0))
@@ -272,7 +290,7 @@ test 'str tagged template', fn:
       (data $d_1 "foo")
       (data $d_2 "1\\n2")
     )
-    ;; sm:I4QFAJgBAJoBAFwAbgDCAQC-CACWAQC6AQDOAQC6AQDEAQCwAQBuALwBAMIBAK4LAJgBAJgBAGgAegDOAQCeAQCqAQCUAQCWAQDKAQDiAQDQAQE4BJIBAQcJcgEACdAFAHoA5gEAjAEA
+    ;; sm:KIQFAJgBAJoBAFwAggEAgAEAbgDCAQC-CACWAQC6AQDOAQC6AQDEAQCwAQBuALwBAMIBAIIBAIAMAJwBAKYBAJgBAJgBAGgAegDOAQCeAQCqAQCUAQCWAQDKAQDiAQDQAQE4BJIBAQcJcgEACdAFAHoA5gEAjAEA
 
 
 test 'str tagged template escape handling', fn:
@@ -290,6 +308,8 @@ test 'str tagged template escape handling', fn:
         (local.set $:ret_5 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $parts_2 (local.get $:params))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 101))
+        (call $rt/trace.wat:trace_pop (i32.const 0) (i32.const 101))
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $parts_2) (local.get $:args)))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:ret_5))
@@ -311,6 +331,7 @@ test 'str tagged template escape handling', fn:
         (local.set $:args (call $rt/apply.wat:args_empty))
         (local.set $:args (call $rt/apply.wat:args_concat (local.get $:v_20) (local.get $:args)))
         (local.set $:args (call $rt/apply.wat:args_prepend (local.get $:ret_67) (local.get $:args)))
+        (call $rt/trace.wat:trace_mark (i32.const 0) (i32.const 24))
         (return_call $rt/apply.wat:apply_3 (local.get $:args) (local.get $:ctx_param) (local.get $:unwrap_foo_66))
       )
       (func $test::v_83 (type $rt/apply.wat:Fn3) (param $:caps_param (ref null any)) (param $:ctx_param (ref null any)) (param $:params (ref null any))
@@ -372,6 +393,9 @@ test 'str tagged template escape handling', fn:
         (local $:caps_arg (ref null $rt/apply.wat:Captures))
         (local $:lit_13 (ref null any))
         (local $:lit_12 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_1 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_3 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_foo_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:foo (local.get $:cell_foo_0))
@@ -417,7 +441,7 @@ test 'str tagged template escape handling', fn:
       (data $d_3 "bar")
       (data $d_4 "\\b\\v\\$\\'\\\\\\xC3\\xA9\\u{8A_9E}")
     )
-    ;; sm:P4YFAJgBAJoBAFwAbgDCAQC-CACWAQC6AQDOAQC6AQDEAQCwAQBuALwBAMIBALwJAJYBALoBAM4BALoBAMQBAOIBANABAUgIkgEBBy6aCwCWAQC6AQDOAQC6AQDEAQDOAQC6AQDiAQDQAQCwAQEALugOAJgBAJgBAGgAmAEAaAB6ANABAJ4BAKoBAJQBAJYBAMoBAQ8DhgEAoAEAqgEAlAEAlgEAygEAkAIA0AEBNBuUAQEjLnIBAC7QBQB6AOYBAIwBAA
+    ;; sm:RIYFAJgBAJoBAFwAhAEAggEAbgDCAQC-CACWAQC6AQDOAQC6AQDEAQCwAQBuALwBAMIBAIIBALwJAJYBALoBAM4BALoBAMQBAOIBANABAUgIkgEBBy6aCwCWAQC6AQDOAQC6AQDEAQDOAQC6AQDiAQDQAQCwAQEALroPAJwBAKYBAJgBAJgBAGgAmAEAaAB6ANABAJ4BAKoBAJQBAJYBAMoBAQ8DhgEAoAEAqgEAlAEAlgEAygEAkAIA0AEBNBuUAQEjLnIBAC7QBQB6AOYBAIwBAA
 
 
 test 'str implicit formatting handling', fn:
@@ -432,6 +456,9 @@ test 'str implicit formatting handling', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_1 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (call $std/str.fnk:from_data (data.ref $d_0 5)))
         (local.set $:args (call $rt/apply.wat:args_empty))
@@ -450,7 +477,7 @@ test 'str implicit formatting handling', fn:
       (data $d_0 "1\0a2\0a3")
       (data $d_1 "test")
     )
-    ;; sm:CZAFAJgBAQANkAEAbgDAAQCmBQB6AOYBAIwBAA
+    ;; sm:C-IFAJwBAKYBAJgBAQANkAEAbgDAAQCmBQB6AOYBAIwBAA
 
 
 test 'str implicit formatting escapes', fn:
@@ -463,6 +490,9 @@ test 'str implicit formatting escapes', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_1 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (call $std/str.fnk:from_data (data.ref $d_0 14)))
         (local.set $:args (call $rt/apply.wat:args_empty))
@@ -481,7 +511,7 @@ test 'str implicit formatting escapes', fn:
       (data $d_0 "\0a\0d\09\0c\08\0b$'\\\c3\a9\e8\aa\9e")
       (data $d_1 "test")
     )
-    ;; sm:CZAFAJgBAQAlkgEAbgDAAQCmBQB6AOYBAIwBAA
+    ;; sm:C-IFAJwBAKYBAJgBAQAlkgEAbgDAAQCmBQB6AOYBAIwBAA
 
 
 test 'empty string eq', fn:
@@ -494,6 +524,9 @@ test 'empty string eq', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:lit_2 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (call $std/str.fnk:str_empty))
         (local.set $:lit_2 (call $std/str.fnk:str_empty))
@@ -510,7 +543,7 @@ test 'empty string eq', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CJwFAJgBAQACbAEMAmwBCwjWBQB6AOYBAIwBAA
+    ;; sm:Cu4FAJwBAKYBAJgBAQACbAEMAmwBCwjWBQB6AOYBAIwBAA
 
 
 # TODO: move to ./test_patterns.fnk
@@ -708,6 +741,7 @@ test 'match empty string', fn:
         (local.set $:ret_4 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:params (call $rt/apply.wat:args_tail (local.get $:params)))
         (local.set $x_1 (call $rt/apply.wat:args_head (local.get $:params)))
+        (call $rt/trace.wat:trace_push (i32.const 0) (i32.const 215))
         (local.set $:caps_arg (ref.null $rt/apply.wat:Captures))
         (local.set $:v_29 (struct.new $rt/apply.wat:Closure (ref.func $test::v_209) (local.get $:caps_arg)))
         (local.set $:caps_arg (array.new_fixed $rt/apply.wat:Captures 1 (local.get $:v_29)))
@@ -733,6 +767,9 @@ test 'match empty string', fn:
         (local $:pub_name (ref null any))
         (local $:unwrap_main_0 (ref null any))
         (local $:args (ref any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_2 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:cell_main_0 (struct.new $rt/apply.wat:Cell (ref.null any)))
         (global.set $test:main (local.get $:cell_main_0))
@@ -761,7 +798,7 @@ test 'match empty string', fn:
       (data $d_0 "test")
       (data $d_1 "main")
     )
-    ;; sm:d4gFAJoBAUABigEAbgDCAQC4BgC6AQDCAQDIAQBuAMYBALIIAJYBALoBAMgBAMgBAIYBAHwAyAwAnAEAmgEAnAEAmgEAlgEA5AEA1AEBBwJuAQAC2AoAmgEAmgEAmgEAmgEAlAEAugEAwgEA3gEA0gEAegDSAQBuALwBAMIBAL4BAMgFAJoBARoBigEAbgDCAQDEBwCcAQCaAQCcAQCaAQCWAQC6AQDCAQBuAMQBAIAEAFgAhAcAugEAwgEAxgEAwgEAegDUAQBuAMABAMABAMQBAPQIAJoBAJoBAJYBALoBAMIBAMIBAIQCANQBAG4AvgEAwAEAwgEAzgwAmAEAmgEAkgEAegDSAQCyAQDSAQB6ANIBALIBANIBANgBANIBAG4AugEAwAEA6gkAmAEAmgEAbAB6ANABAKABAK4BAJQBAJYBAMwBALQBAG4A0AEApgUAegDmAQCMAQA
+    ;; sm:eogFAJoBAUABigEAbgDCAQC4BgC6AQDCAQDIAQBuAMYBALIIAJYBALoBAMgBAMgBAIYBAHwAyAwAnAEAmgEAnAEAmgEAlgEA5AEA1AEBBwJuAQAC2AoAmgEAmgEAmgEAmgEAlAEAugEAwgEA3gEA0gEAegDSAQBuALwBAMIBAL4BAMgFAJoBARoBigEAbgDCAQDEBwCcAQCaAQCcAQCaAQCWAQC6AQDCAQBuAMQBAIAEAFgAhAcAugEAwgEAxgEAwgEAegDUAQBuAMABAMABAMQBAPQIAJoBAJoBAJYBALoBAMIBAMIBAIQCANQBAG4AvgEAwAEAwgEAzgwAmAEAmgEAkgEAhAEAegDSAQCyAQDSAQB6ANIBALIBANIBANgBANIBAG4AugEAwAEAvAoAnAEApgEAmAEAmgEAbAB6ANABAKABAK4BAJQBAJYBAMwBALQBAG4A0AEApgUAegDmAQCMAQA
 
 
 test 'empty string eq template', fn:
@@ -774,6 +811,9 @@ test 'empty string eq template', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:lit_2 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_0 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (call $std/str.fnk:str_empty))
         (local.set $:lit_2 (call $std/str.fnk:str_empty))
@@ -790,7 +830,7 @@ test 'empty string eq template', fn:
       )
       (data $d_0 "test")
     )
-    ;; sm:CJwFAJgBAQACbAEMB2wBCw3WBQB6AOYBAIwBAA
+    ;; sm:Cu4FAJwBAKYBAJgBAQACbAEMB2wBCw3WBQB6AOYBAIwBAA
 
 
 test 'str eq', fn:
@@ -803,6 +843,9 @@ test 'str eq', fn:
         (local $:ret_0 (ref null any))
         (local $:lit_1 (ref null any))
         (local $:lit_2 (ref null any))
+        (local $:mod_reg_url (ref null any))
+        (local.set $:mod_reg_url (call $std/str.fnk:from_data (data.ref $d_1 4)))
+        (call $rt/modules.wat:register_module (i32.const 0) (local.get $:mod_reg_url))
         (local.set $:ret_0 (call $rt/apply.wat:args_head (local.get $:params)))
         (local.set $:lit_1 (call $std/str.fnk:from_data (data.ref $d_0 5)))
         (local.set $:lit_2 (call $std/str.fnk:from_data (data.ref $d_0 5)))
@@ -820,5 +863,7 @@ test 'str eq', fn:
       (data $d_0 "hello")
       (data $d_1 "test")
     )
-    ;; sm:CJwFAJgBAQAHkAEBFgeQAQEVEtYFAHoA5gEAjAEA
+    ;; sm:Cu4FAJwBAKYBAJgBAQAHkAEBFgeQAQEVEtYFAHoA5gEAjAEA
+
+
 
diff --git a/src/runner/wasmtime_runner.rs b/src/runner/wasmtime_runner.rs
index 87cf5f2..067f042 100644
--- a/src/runner/wasmtime_runner.rs
+++ b/src/runner/wasmtime_runner.rs
@@ -79,6 +79,14 @@ pub fn run(
   let exit_state: Arc<Mutex<ExitState>> = Arc::new(Mutex::new(ExitState::default()));
   let cli_args = Arc::new(args);
 
+  // (module_id, cps_id) -> source line, built from the debug marks. Lets
+  // the trace's `get_loc` resolve a frame's (mid, cid) to a source line.
+  let loc_map: Arc<std::collections::HashMap<(u32, u32), u32>> = Arc::new(
+    wasm.marks.iter()
+      .map(|m| ((m.module_id.0, m.cps_id.0), m.source.start.line))
+      .collect(),
+  );
+
   let mut linker = Linker::new(&engine);
   for import in module.imports() {
     if import.module() == "env"
@@ -102,6 +110,18 @@ pub fn run(
             Ok(())
           }).map_err(|e| e.to_string())?;
         }
+        "host_resolve_loc" => {
+          // (module_id, cps_id) -> source line (0 if unknown). Backs the
+          // trace's get_loc; resolves a frame to a source location.
+          let lm = loc_map.clone();
+          linker.func_new("env", &name, ft, move |_caller, params, results| {
+            let mid = params[0].unwrap_i32() as u32;
+            let cid = params[1].unwrap_i32() as u32;
+            let line = lm.get(&(mid, cid)).copied().unwrap_or(0);
+            results[0] = Val::I32(line as i32);
+            Ok(())
+          }).map_err(|e| e.to_string())?;
+        }
         "host_read_sync" => {
           let input = stdin.clone();
           linker.func_new("env", &name, ft, move |mut caller, params, results| {
diff --git a/src/runtime/interop/js/fink.js b/src/runtime/interop/js/fink.js
index 108f81f..941c60a 100644
--- a/src/runtime/interop/js/fink.js
+++ b/src/runtime/interop/js/fink.js
@@ -267,6 +267,10 @@ export const init_wasm = async (bytes, host = {}) => {
     host_write,
     host_read_sync:    (_fd, _size, _ptr) => 0,
     host_invoke_cont:  (resolver, args, ctx) => resolver(args, ctx),
+    // Trace source-line resolution needs the compiled debug marks, which
+    // the wasm+js artifact does not carry. Return 0 (the import's
+    // "unknown" sentinel) so get_loc yields no line in the JS host.
+    host_resolve_loc:  (_mid, _cid) => 0,
   };
 
   const { instance } = await WebAssembly.instantiate(bytes, { env });
diff --git a/src/runtime/interop/js/interop.wat b/src/runtime/interop/js/interop.wat
index 3955daa..dde5d04 100644
--- a/src/runtime/interop/js/interop.wat
+++ b/src/runtime/interop/js/interop.wat
@@ -76,6 +76,15 @@
       (param $args (ref null any))
       (param $ctx (ref null any))
       (param $callee (ref null any))))
+  ;; Keep rt/trace.wat's instrumentation primitives in the link and alive:
+  ;; user fragments call them from lowered code, but no runtime module
+  ;; references them. (get_trace is kept alive via std/trace.fnk's import.)
+  (import "rt/trace.wat" "trace_push"
+    (func $trace_push (param i32) (param i32)))
+  (import "rt/trace.wat" "trace_mark"
+    (func $trace_mark (param i32) (param i32)))
+  (import "rt/trace.wat" "trace_pop"
+    (func $trace_pop (param i32) (param i32)))
   (import "rt/apply.wat" "empty_ctx"
     (func $empty_ctx_inner (result (ref any))))
   (import "rt/apply.wat" "set_ctx"
diff --git a/src/runtime/interop/rust/interop.wat b/src/runtime/interop/rust/interop.wat
index bcce381..e242a29 100644
--- a/src/runtime/interop/rust/interop.wat
+++ b/src/runtime/interop/rust/interop.wat
@@ -61,6 +61,15 @@
       (param $args (ref null any))
       (param $ctx (ref null any))
       (param $callee (ref null any))))
+  ;; Keep rt/trace.wat's instrumentation primitives in the link and alive:
+  ;; user fragments call them from lowered code, but no runtime module
+  ;; references them. (get_trace is kept alive via std/trace.fnk's import.)
+  (import "rt/trace.wat"    "trace_push"
+    (func $trace_push (param i32) (param i32)))
+  (import "rt/trace.wat"    "trace_mark"
+    (func $trace_mark (param i32) (param i32)))
+  (import "rt/trace.wat"    "trace_pop"
+    (func $trace_pop (param i32) (param i32)))
   (import "rt/apply.wat"    "empty_ctx"
     (func $empty_ctx (result (ref any))))
   (import "rt/apply.wat" "set_ctx"
diff --git a/src/runtime/rt/modules.wat b/src/runtime/rt/modules.wat
index c242a0c..b4ae173 100644
--- a/src/runtime/rt/modules.wat
+++ b/src/runtime/rt/modules.wat
@@ -65,6 +65,21 @@
   (import "std/list.wat"  "prepend"
     (func $list_prepend (param $head (ref any)) (param $tail (ref $List)) (result (ref $List))))
 
+  ;; Args machinery + int unboxing for the fink-callable get_module_url
+  ;; Fn3 wrapper.
+  (import "rt/apply.wat" "args_head"
+    (func $args_head (param (ref null any)) (result (ref null any))))
+  (import "rt/apply.wat" "args_tail"
+    (func $args_tail (param (ref null any)) (result (ref null any))))
+  (import "rt/apply.wat" "args_empty"
+    (func $args_empty (result (ref any))))
+  (import "rt/apply.wat" "args_prepend"
+    (func $args_prepend (param (ref null any)) (param (ref any)) (result (ref any))))
+  (import "std/num.wat" "Num" (type $Num (sub any)))
+  (import "std/int.wat" "Int" (type $Int (sub $Num (struct))))
+  (import "std/int.wat" "_int_ival"
+    (func $int_ival (param (ref $Int)) (result i64)))
+
 
   ;; -- Registry -------------------------------------------------------
 
@@ -72,6 +87,122 @@
   ;; Stored as $Rec so we can call rec_get/put_field directly.
   (global $registry (mut (ref null $Rec)) (ref.null $Rec))
 
+
+  ;; -- Module-id → url array ------------------------------------------
+  ;;
+  ;; The trace buffer records call sites as (module_id, cps_id) i32 pairs
+  ;; (rt/trace.wat). Resolving a frame back to a source location needs
+  ;; module_id → url. ModuleId is a compile-time concept that does not
+  ;; otherwise exist in the runtime, so each module self-registers its
+  ;; own (id, url) from its fink_module via `register_module`.
+  ;;
+  ;; A GC array indexed directly by module_id (not a wasm table). Module
+  ;; ids are small dense ints assigned in BFS order by compile_package.
+  ;; It grows by 100 slots at a time (array.copy into a bigger array, the
+  ;; same idiom dict.wat/set.wat use) when an id exceeds capacity.
+  (type $ModuleUrls (array (mut (ref null any))))
+  (global $module_urls (mut (ref null $ModuleUrls)) (ref.null $ModuleUrls))
+
+  ;; Record module_id → url. Idempotent: re-registering the same id with
+  ;; the same url is a harmless overwrite (fink_module may run more than
+  ;; once). Lazy-allocates and grows the table as needed.
+  (func $register_module (@pub)
+    (param $id i32)
+    (param $url (ref null any))
+    (local $old (ref null $ModuleUrls))
+    (local $new_len i32)
+    (local $new (ref $ModuleUrls))
+
+    (local.set $old (global.get $module_urls))
+
+    ;; Grow (or allocate) if id is out of the current bounds.
+    (if (i32.ge_u
+          (local.get $id)
+          (if (result i32) (ref.is_null (local.get $old))
+            (then (i32.const 0))
+            (else (array.len (ref.as_non_null (local.get $old))))))
+      (then
+        ;; new_len = max(old_len + 100, id + 1) so a single large id
+        ;; can't outpace the growth step.
+        (local.set $new_len
+          (i32.add
+            (if (result i32) (ref.is_null (local.get $old))
+              (then (i32.const 0))
+              (else (array.len (ref.as_non_null (local.get $old)))))
+            (i32.const 100)))
+        (if (i32.gt_u (i32.add (local.get $id) (i32.const 1)) (local.get $new_len))
+          (then (local.set $new_len (i32.add (local.get $id) (i32.const 1)))))
+
+        (local.set $new (array.new $ModuleUrls (ref.null any) (local.get $new_len)))
+        (if (i32.eqz (ref.is_null (local.get $old)))
+          (then
+            (array.copy $ModuleUrls $ModuleUrls
+              (local.get $new) (i32.const 0)
+              (ref.as_non_null (local.get $old)) (i32.const 0)
+              (array.len (ref.as_non_null (local.get $old))))))
+        (global.set $module_urls (local.get $new))))
+
+    (array.set $ModuleUrls
+      (ref.as_non_null (global.get $module_urls))
+      (local.get $id)
+      (local.get $url)))
+
+  ;; Look up the url registered for module_id, or null if unregistered
+  ;; or out of bounds. Raw i32 worker; the fink-callable entry is the
+  ;; Fn3 wrapper below.
+  (func $_get_module_url
+    (param $id i32)
+    (result (ref null any))
+    (if (ref.is_null (global.get $module_urls))
+      (then (return (ref.null any))))
+    (if (i32.ge_u
+          (local.get $id)
+          (array.len (ref.as_non_null (global.get $module_urls))))
+      (then (return (ref.null any))))
+    (array.get $ModuleUrls
+      (ref.as_non_null (global.get $module_urls))
+      (local.get $id)))
+
+  ;; Fink-callable entry: `get_module_url mod_id`. CPS-lowered args =
+  ;; [k_caller, mod_id]. mod_id arrives as a boxed $Int; unbox, look up,
+  ;; tail-call k_caller with the url (or null).
+  (elem declare func $get_module_url_apply)
+
+  (func $get_module_url_apply (type $Fn3)
+      (param $_caps (ref null any))
+      (param $ctx (ref null any))
+      (param $args (ref null any))
+    (local $k_caller (ref any))
+    (local $id (ref null any))
+    (local $rest (ref null any))
+    (local $url (ref null any))
+    (local $k_args (ref any))
+
+    (local.set $k_caller (ref.as_non_null (call $args_head (local.get $args))))
+    (local.set $rest (call $args_tail (local.get $args)))
+    (local.set $id (call $args_head (local.get $rest)))
+
+    (local.set $url
+      (call $_get_module_url
+        (i32.wrap_i64
+          (call $int_ival (ref.cast (ref $Int) (local.get $id))))))
+
+    (local.set $k_args (call $args_empty))
+    (local.set $k_args (call $args_prepend (local.get $url) (local.get $k_args)))
+    (return_call $apply_3
+      (local.get $k_args)
+      (local.get $ctx)
+      (local.get $k_caller)))
+
+  (global $get_module_url_closure (ref $Closure)
+    (struct.new $Closure
+      (ref.func $get_module_url_apply)
+      (ref.null $Captures)))
+
+  (func $get_module_url (@pub)
+      (result (ref any))
+    (global.get $get_module_url_closure))
+
   ;; -- init -----------------------------------------------------------
   ;;
   ;; Direct call. Returns 1 if this is the first call for `mod_url`
diff --git a/src/runtime/rt/trace.wat b/src/runtime/rt/trace.wat
new file mode 100644
index 0000000..4946515
--- /dev/null
+++ b/src/runtime/rt/trace.wat
@@ -0,0 +1,273 @@
+;; Trace buffer -- a bounded stack of userland function activations.
+;;
+;; This is a real backtrace, not a recency log. Each frame is one userland
+;; function activation; the live stack of frames is the current call chain.
+;; Because Fink compiles every call to a tail call, there is no native wasm
+;; call stack to walk; this stack is the portable substitute -- it lives in
+;; linear memory so a host can read it even after a hard trap, on any
+;; runtime, not just the wasmtime debugger.
+;;
+;; Three primitives drive it (all carry the full (mid, cid) pair; the
+;; redundancy is a dev-time balance check, removable later):
+;;   trace_push(mid, cid) -- enter a userland fn defined at (mid, cid):
+;;                           push a frame stamped with that identity.
+;;   trace_mark(mid, cid) -- a call site (mid, cid) within the current fn:
+;;                           update the top frame's current-call-site fields.
+;;   trace_pop(mid, cid)  -- leave fn (mid, cid): pop the top frame.
+;;
+;; Frame = 4 x i32 = 16 bytes: { fn_mid, fn_cid, call_mid, call_cid }.
+;;   fn_*   -- the function's identity (stamped by push).
+;;   call_* -- where in the function we currently are (set by mark; 0 until
+;;             the first call).
+;;
+;; Bounded window of TRACE_CAP frames. trace_depth is the logical depth and
+;; may exceed TRACE_CAP; storage is a ring of TRACE_CAP frames indexed by
+;; (depth mod TRACE_CAP), so a push when full overwrites the oldest (bottom,
+;; main-ward) frame and a pop at depth 0 is a no-op. The window size is all
+;; that bounds how deep the backtrace goes.
+;;
+;; The user fragment brings memory 0; this module doesn't declare its own,
+;; matching interop.wat.
+
+(module
+
+  (import "rt/apply.wat" "Fn3"      (type $Fn3      (sub any)))
+  (import "rt/apply.wat" "Closure"  (type $Closure  (sub any)))
+  (import "rt/apply.wat" "Captures" (type $Captures (sub any)))
+  (import "rt/apply.wat" "args_empty"
+    (func $args_empty (result (ref any))))
+  (import "rt/apply.wat" "args_prepend"
+    (func $args_prepend (param (ref null any)) (param (ref any)) (result (ref any))))
+  (import "rt/apply.wat" "args_head"
+    (func $args_head (param (ref null any)) (result (ref null any))))
+  (import "rt/apply.wat" "args_tail"
+    (func $args_tail (param (ref null any)) (result (ref null any))))
+  (import "rt/apply.wat" "apply_3"
+    (func $apply_3
+      (param (ref null any)) (param (ref null any)) (param (ref null any))))
+
+  (import "std/list.wat" "List" (type $List (sub any)))
+  (import "std/list.wat" "empty"
+    (func $list_empty (result (ref $List))))
+  (import "std/list.wat" "prepend"
+    (func $list_prepend (param (ref any)) (param (ref $List)) (result (ref $List))))
+
+  (import "std/num.wat" "Num" (type $Num (sub any)))
+  (import "std/int.wat" "Int" (type $Int (sub $Num (struct))))
+  (import "std/int.wat" "I64" (type $I64 (sub $Int (struct (field $ival i64)))))
+  (import "std/int.wat" "_box_i64"
+    (func $box_i64 (param i64) (result (ref $I64))))
+  (import "std/int.wat" "_int_ival"
+    (func $int_ival (param (ref $Int)) (result i64)))
+
+  ;; Host resolves (module_id, cps_id) -> source line (0 if unknown), via
+  ;; the compiled debug marks. Backs the fink-callable get_loc.
+  (import "env" "host_resolve_loc"
+    (func $host_resolve_loc (param i32) (param i32) (result i32)))
+
+  ;; Window capacity in frames.
+  (global $TRACE_CAP i32 (i32.const 64))
+  ;; Bytes per frame: 4 x i32 = { fn_mid, fn_cid, call_mid, call_cid }.
+  (global $FRAME_BYTES i32 (i32.const 16))
+  ;; Byte offset of the frame region (bottom of memory).
+  (global $trace_base i32 (i32.const 0))
+  ;; Logical stack depth. May exceed TRACE_CAP; storage wraps mod TRACE_CAP.
+  (global $trace_depth (mut i32) (i32.const 0))
+
+  ;; Byte address of the frame at logical index `idx` (idx mod TRACE_CAP).
+  (func $frame_addr (param $idx i32) (result i32)
+    (i32.add
+      (global.get $trace_base)
+      (i32.mul
+        (i32.rem_u (local.get $idx) (global.get $TRACE_CAP))
+        (global.get $FRAME_BYTES))))
+
+  ;; Enter a userland fn defined at (mid, cid): push a frame stamped with
+  ;; that identity, call site cleared. depth++ (storage wraps when full,
+  ;; dropping the oldest frame).
+  (func $trace_push (@pub)
+      (param $fn_mid i32)
+      (param $fn_cid i32)
+    (local $addr i32)
+    (local.set $addr (call $frame_addr (global.get $trace_depth)))
+    (i32.store         (local.get $addr)                  (local.get $fn_mid))
+    (i32.store offset=4  (local.get $addr)                (local.get $fn_cid))
+    (i32.store offset=8  (local.get $addr) (i32.const 0))  ;; call_mid
+    (i32.store offset=12 (local.get $addr) (i32.const 0))  ;; call_cid
+    (global.set $trace_depth (i32.add (global.get $trace_depth) (i32.const 1))))
+
+  ;; A call site (mid, cid) within the current fn: update the top frame's
+  ;; current-call-site fields. No-op if the stack is empty.
+  (func $trace_mark (@pub)
+      (param $call_mid i32)
+      (param $call_cid i32)
+    (local $addr i32)
+    (if (i32.eqz (global.get $trace_depth))
+      (then (return)))
+    (local.set $addr
+      (call $frame_addr (i32.sub (global.get $trace_depth) (i32.const 1))))
+    (i32.store offset=8  (local.get $addr) (local.get $call_mid))
+    (i32.store offset=12 (local.get $addr) (local.get $call_cid)))
+
+  ;; Leave fn (mid, cid): pop the top frame. No-op at depth 0 (a pop of a
+  ;; frame that aged out of the bounded window). The (mid, cid) args are
+  ;; carried for a future balance assert; unused for now.
+  (func $trace_pop (@pub)
+      (param $fn_mid i32)
+      (param $fn_cid i32)
+    (if (i32.eqz (global.get $trace_depth))
+      (then (return)))
+    (global.set $trace_depth (i32.sub (global.get $trace_depth) (i32.const 1))))
+
+  ;; Read up to `depth` innermost frames as a fink list of
+  ;; [call_mid, call_cid] pairs -- the current call site of each live
+  ;; function, newest (innermost) first. Walks the stack top-down. A frame
+  ;; whose call site is still 0 (entered, not yet at a call) is emitted as
+  ;; [fn_mid, fn_cid] instead, so the innermost frame always carries a
+  ;; useful location.
+  (func $read_trace
+      (param $depth i32)
+      (result (ref $List))
+    (local $n i32)
+    (local $avail i32)
+    (local $i i32)
+    (local $addr i32)
+    (local $mid i32)
+    (local $cid i32)
+    (local $result (ref $List))
+    (local $frame (ref $List))
+
+    ;; avail = min(trace_depth, TRACE_CAP); n = min(depth, avail).
+    (local.set $avail
+      (select (global.get $trace_depth) (global.get $TRACE_CAP)
+        (i32.le_u (global.get $trace_depth) (global.get $TRACE_CAP))))
+    (local.set $n
+      (select (local.get $depth) (local.get $avail)
+        (i32.le_u (local.get $depth) (local.get $avail))))
+
+    (local.set $result (call $list_empty))
+
+    ;; Walk bottom-up over the window so that prepending leaves the
+    ;; newest (innermost) frame at the head - conventional backtrace order
+    ;; (get_trace's own call site first, callers after). The oldest
+    ;; in-window frame is logical index (trace_depth - n); the i-th walked
+    ;; is (trace_depth - n + i).
+    (local.set $i (i32.const 0))
+    (block $done (loop $next
+      (br_if $done (i32.ge_u (local.get $i) (local.get $n)))
+
+      (local.set $addr
+        (call $frame_addr
+          (i32.add
+            (i32.sub (global.get $trace_depth) (local.get $n))
+            (local.get $i))))
+
+      ;; Prefer the current call site; fall back to fn identity if no call
+      ;; has been marked yet (call_cid == 0).
+      (local.set $cid (i32.load offset=12 (local.get $addr)))
+      (if (i32.eqz (local.get $cid))
+        (then
+          (local.set $mid (i32.load        (local.get $addr)))
+          (local.set $cid (i32.load offset=4 (local.get $addr))))
+        (else
+          (local.set $mid (i32.load offset=8 (local.get $addr)))))
+
+      (local.set $frame
+        (call $list_prepend
+          (call $box_i64 (i64.extend_i32_u (local.get $mid)))
+          (call $list_prepend
+            (call $box_i64 (i64.extend_i32_u (local.get $cid)))
+            (call $list_empty))))
+      (local.set $result
+        (call $list_prepend (local.get $frame) (local.get $result)))
+
+      (local.set $i (i32.add (local.get $i) (i32.const 1)))
+      (br $next)))
+
+    (local.get $result))
+
+  ;; Fink-callable entry: `get_trace depth`.
+  ;; CPS-lowered args = [k_caller, depth]. `depth` arrives as a boxed $Int;
+  ;; unbox it, read the stack, tail-call k_caller with the list.
+  (elem declare func $get_trace_apply)
+
+  (func $get_trace_apply (type $Fn3)
+      (param $_caps (ref null any))
+      (param $ctx (ref null any))
+      (param $args (ref null any))
+    (local $k_caller (ref any))
+    (local $depth (ref null any))
+    (local $rest (ref null any))
+    (local $trace (ref $List))
+    (local $k_args (ref any))
+
+    (local.set $k_caller (ref.as_non_null (call $args_head (local.get $args))))
+    (local.set $rest (call $args_tail (local.get $args)))
+    (local.set $depth (call $args_head (local.get $rest)))
+
+    (local.set $trace
+      (call $read_trace
+        (i32.wrap_i64
+          (call $int_ival (ref.cast (ref $Int) (local.get $depth))))))
+
+    (local.set $k_args (call $args_empty))
+    (local.set $k_args (call $args_prepend (local.get $trace) (local.get $k_args)))
+    (return_call $apply_3
+      (local.get $k_args)
+      (local.get $ctx)
+      (local.get $k_caller)))
+
+  (global $get_trace_closure (ref $Closure)
+    (struct.new $Closure
+      (ref.func $get_trace_apply)
+      (ref.null $Captures)))
+
+  (func $get_trace (@pub)
+      (result (ref any))
+    (global.get $get_trace_closure))
+
+  ;; Fink-callable entry: `get_loc mid, cid` -> source line (0 if unknown).
+  ;; CPS-lowered args = [k_caller, mid, cid], both boxed $Int.
+  (elem declare func $get_loc_apply)
+
+  (func $get_loc_apply (type $Fn3)
+      (param $_caps (ref null any))
+      (param $ctx (ref null any))
+      (param $args (ref null any))
+    (local $k_caller (ref any))
+    (local $rest (ref null any))
+    (local $mid (ref null any))
+    (local $cid (ref null any))
+    (local $line i32)
+    (local $k_args (ref any))
+
+    (local.set $k_caller (ref.as_non_null (call $args_head (local.get $args))))
+    (local.set $rest (call $args_tail (local.get $args)))
+    (local.set $mid (call $args_head (local.get $rest)))
+    (local.set $rest (call $args_tail (local.get $rest)))
+    (local.set $cid (call $args_head (local.get $rest)))
+
+    (local.set $line
+      (call $host_resolve_loc
+        (i32.wrap_i64 (call $int_ival (ref.cast (ref $Int) (local.get $mid))))
+        (i32.wrap_i64 (call $int_ival (ref.cast (ref $Int) (local.get $cid))))))
+
+    (local.set $k_args (call $args_empty))
+    (local.set $k_args
+      (call $args_prepend
+        (call $box_i64 (i64.extend_i32_u (local.get $line)))
+        (local.get $k_args)))
+    (return_call $apply_3
+      (local.get $k_args)
+      (local.get $ctx)
+      (local.get $k_caller)))
+
+  (global $get_loc_closure (ref $Closure)
+    (struct.new $Closure
+      (ref.func $get_loc_apply)
+      (ref.null $Captures)))
+
+  (func $get_loc (@pub)
+      (result (ref any))
+    (global.get $get_loc_closure))
+)
diff --git a/std/all.test.fnk b/std/all.test.fnk
index 98e3231..b69ec5e 100644
--- a/std/all.test.fnk
+++ b/std/all.test.fnk
@@ -5,6 +5,7 @@ import './tasks.test.fnk'
 import './channels.test.fnk'
 import './effects.test.fnk'
 import './io.test.fnk'
+import './trace.test.fnk'
 
 
 
diff --git a/std/testing.fnk b/std/testing.fnk
index c4deafd..30f7979 100644
--- a/std/testing.fnk
+++ b/std/testing.fnk
@@ -1,6 +1,7 @@
 
 {write, stderr} = import 'std/io.fnk'
-{suspend, unique, init_ctx} = import 'std/effects.fnk'
+{suspend, init_ctx} = import 'std/effects.fnk'
+{get_trace, get_module_url, get_loc} = import 'std/trace.fnk'
 
 
 test = fn name, body:
@@ -17,7 +18,7 @@ upd_curr_test = fn upd_fn:
 
 
 set_curr_test = fn test_case:
-  upd_tests fn ctx:
+  upd_tests fn _:
     [test_case, {curr: test_case}]
 
 
@@ -48,7 +49,20 @@ run_test = fn test_case:
       true
 
 
-fail = fn failure:
+trace_to_str = fn t, s:
+  match t:
+    []: s
+    [[mid, cid], ..rest]:
+      murl = get_module_url mid
+      trace_to_str rest, '${s}\n  ${murl}:${get_loc mid, cid} (${mid}:${cid})'
+
+
+
+fail = fn msg:
+  trace = get_trace 5
+
+  failure = trace_to_str trace, '${msg}\nTraceback:'
+
   abort = upd_curr_test fn {abort}:
     [abort, {result: {failure}}]
 
@@ -81,7 +95,7 @@ test_all = fn:
 equals = fn actual, expected:
   match actual == expected:
     true: true
-    false: fail '${actual}\n  !=\n  ${expected}'
+    false: fail 'act: ${actual}\n  !=\n  exp: ${expected}'
 
 
 
diff --git a/std/trace.fnk b/std/trace.fnk
new file mode 100644
index 0000000..4556965
--- /dev/null
+++ b/std/trace.fnk
@@ -0,0 +1,10 @@
+{get_module_url: rt_get_module_url} = import 'rt/modules.wat'
+{get_trace: rt_get_trace, get_loc: rt_get_loc} = import 'rt/trace.wat'
+
+
+get_loc = rt_get_loc
+
+get_trace = rt_get_trace
+
+
+get_module_url = rt_get_module_url
\ No newline at end of file
diff --git a/std/trace.test.fnk b/std/trace.test.fnk
new file mode 100644
index 0000000..b1728af
--- /dev/null
+++ b/std/trace.test.fnk
@@ -0,0 +1,41 @@
+{test, equals} = import 'std/testing.fnk'
+
+{get_trace, get_module_url, get_loc} = import 'std/trace.fnk'
+
+
+
+trace_to_str = fn t, s:
+  match t:
+    []: s
+    [[mid, cid], ..rest]:
+      murl = get_module_url mid
+      trace_to_str rest, '${s}\n  ${murl}:${get_loc mid, cid}'
+
+
+
+# test 'foooooobar', fn:
+#   equals
+#     41
+#     42
+
+
+test 'get_trace', fn:
+  bar = fn depth:
+    get_trace depth
+
+  [_, ..foo_t] = get_trace 4
+  [_, _, ..bar_t] = bar 5
+
+  equals
+    trace_to_str foo_t, ''
+    trace_to_str bar_t, ''
+
+
+
+
+test 'get_module_url', fn:
+  [[mod_id, _]] = get_trace 1
+
+  equals
+    get_module_url mod_id
+    './trace.test.fnk'