perf(container): inline the resolve_provider body into resolve

architecture/concurrency.md

@@ -32,8 +32,8 @@ state at a single-threaded edge, nothing prevents several threads from then
 independently calling `resolve` on that (now-closed) container at once — each
 unaware the others are doing the same. A container is open from construction
 (see [containers.md](containers.md#optional-open-lifecycle)), so this is the
-only path back to `closed = True` in the first place. `resolve_provider` calls
-`_prepare()` whenever `self.closed` is `True`; `_prepare()` warns and sets
+only path back to `closed = True` in the first place. `resolve` and
+`resolve_provider` each call `_prepare()` whenever `self.closed` is `True`; `_prepare()` warns and sets
 `closed = False`, unlocked. The reopen needs no lock because it is idempotent —
 N threads racing a closed container all write the same `False`, and they go on
 to share one singleton via the cache lock below. What is *not* serialized is the

architecture/containers.md

@@ -137,7 +137,7 @@ explicitly under `Container` rather than inferred from a type annotation).
    `close_async()` can clean them up.
 
 2. **`closed = True`** — set in a `finally` block, even if finalizers raised. A subsequent
-   `resolve_provider` (or a nested provider resolving at a closed ancestor scope) self-heals: it
+   `resolve` / `resolve_provider` (or a nested provider resolving at a closed ancestor scope) self-heals: it
    reopens the container via `_prepare()` and emits `ContainerClosedWarning`, rather than raising.
    Re-enter the container via `with`/`async with`, or call `container.open()`, for a silent reopen
    instead — see [Optional-open lifecycle](#optional-open-lifecycle).
@@ -157,9 +157,11 @@ close, ready to be returned again without re-running the creator.
 
 ### Open and reopen (context-manager protocol)
 
-`_prepare()` — not `open()` — is the primitive the resolve path calls: `resolve_provider` (and the
-compiled-resolver dispatch it wraps) calls it whenever `self.closed` is `True`, before doing anything
-else. That caller-side `if closed` check is the only guard: `_prepare()` itself takes no lock and makes
+`_prepare()` — not `open()` — is the primitive the resolve path calls: `resolve_provider` and `resolve`
+(and the compiled-resolver dispatch they wrap) call it whenever `self.closed` is `True`, before doing
+anything else — `resolve` holds its own copy of that check rather than delegating
+([decision](../planning/decisions/2026-08-03-resolve-provider-not-a-seam.md)).
+That caller-side `if closed` check is the only guard: `_prepare()` itself takes no lock and makes
 no re-check, warning with `ContainerClosedWarning` and clearing `closed` unconditionally. Concurrent
 reuse of one closed container therefore warns **at least once**, not exactly once — see
 [concurrency.md](concurrency.md#the-lifecycle). `open()` is a separate, public entry point that clears

architecture/performance.md

@@ -53,21 +53,32 @@ deliberate — there is no interpreted fallback to inherit shared behaviour from
 
 ## Inlined memo hits
 
-Four lookups are hand-inlined across three call sites, with the method called
+Six lookups are hand-inlined across four call sites, with the method called
 only on a miss:
 
 | Call site | Inlines | Method still owns |
 |---|---|---|
 | `Container.resolve_provider` | `providers_registry._resolvers.get(pid)` | the cycle guard and memo write, on a miss |
+| `Container.resolve` | `providers_registry._providers.get(dependency_type)` and `._resolvers.get(pid)` | `find_provider`'s absence result, and `resolver_for`'s cycle guard and memo write, on a miss |
 | `_compile_cached_factory`'s `resolve` | `cache_registry._items.get(pid)` | `setdefault`, which is what makes concurrent first-resolvers share one `CacheItem` |
 | `_compile_alias`'s `resolve` | `providers_registry._providers.get(source_type)` and `._resolvers.get(source.provider_id)` | `_find_source`'s error, and `resolver_for`'s cycle guard and memo write, on a miss |
 
 In each case the method being inlined *opens with exactly that lookup and
 returns*, so the inline is not a reimplementation that can drift — it is the
-method's own fast path, hoisted past its frame. All three keep calling the real
+method's own fast path, hoisted past its frame. All four keep calling the real
 method on a miss, so the miss-path invariants (cycle detection, single shared
 `CacheItem`, the dangling-source error) are untouched.
 
+`Container.resolve` goes further than a hoisted lookup: it carries a **copy of
+`resolve_provider`'s whole body** — the closed check, the memo hit, the
+`resolver_for` fallback, the resolver call and the `RecursionError` conversion.
+That is the one place in the library where a block of logic is deliberately
+duplicated rather than shared, and both copies must be edited together. It is
+worth ~-19% on a by-type resolve, and it is licensed by `resolve_provider` not
+being an interception seam — an override has seen only top-level calls since the
+compiled resolvers landed
+([decision](../planning/decisions/2026-08-03-resolve-provider-not-a-seam.md)).
+
 The alias case inlines two lookups rather than one, because the hop is two indirections deep: without them an
 alias costs four Python frames (`_find_source`, `find_provider`, `resolve_provider`, then the source's
 resolver) where every `Factory` dependency costs one.

architecture/resolution.md

@@ -7,8 +7,10 @@ made true.
 ## Entry points
 
 - `container.resolve(SomeType)` — looks up `SomeType` in `providers_registry` (raising
-  `ProviderNotRegisteredError`, with closest-match suggestions, if none is registered), then delegates to
-  `resolve_provider`.
+  `ProviderNotRegisteredError`, with closest-match suggestions, if none is registered), then dispatches to the
+  compiled resolver itself. It holds its own copy of `resolve_provider`'s body rather than delegating, so the
+  by-type path pays no extra frame; the two copies must be edited together
+  ([decision](../planning/decisions/2026-08-03-resolve-provider-not-a-seam.md)).
 - `container.resolve_provider(provider)` — resolves by provider reference, skipping the registry lookup.
   It reopens the entry container if it was closed (see [containers.md](containers.md#closing)), then calls
   `providers_registry.resolver_for(provider)(self)` and wraps any escaped `RecursionError` (the runtime cycle

architecture/validation.md

@@ -92,8 +92,10 @@ as a resolution breadcrumb — including the aligned scope column — so a cycle
 read identically. See [resolution.md](resolution.md#one-renderer) for that drawer.
 
 > **Runtime resolution has a cycle guard too — but `validate()` remains the way to see all errors up front.**
-> `Container.resolve_provider` wraps the compiled-resolver dispatch (`resolver_for(provider)(self)`) in
-> `try/except RecursionError`. The
+> `Container.resolve_provider` **and `Container.resolve`** each wrap the compiled-resolver dispatch
+> (`resolver_for(provider)(self)`) in `try/except RecursionError` — `resolve` carries its own copy of that
+> body rather than delegating, so the by-type entry point pays no extra frame
+> ([decision](../planning/decisions/2026-08-03-resolve-provider-not-a-seam.md)). The
 > handler first short-circuits: if the registry is already validated (`_validated` is `True`), the static
 > graph is known acyclic, so the overflow is genuine self-recursion and the `RecursionError` re-raises untouched
 > without any walk. Otherwise, when an unvalidated circular graph's first resolve overflows the stack, the handler

modern_di/container.py

@@ -191,15 +191,28 @@ def lock(self) -> "threading.RLock | None":
         return self._lock
 
     def resolve(self, dependency_type: type[types.T]) -> types.T:
-        """Resolve a dependency by its type."""
-        provider = self.providers_registry.find_provider(dependency_type)
-        if not provider:
+        """Resolve a dependency by its type.
+
+        Carries its own copy of `resolve_provider`'s body rather than calling it: the extra
+        frame is ~19% of a by-type resolve. The duplication is deliberate and the two must be
+        edited together -- see planning/decisions/2026-08-03-resolve-provider-not-a-seam.md.
+        """
+        registry = self.providers_registry
+        provider = registry._providers.get(dependency_type)  # noqa: SLF001
+        if provider is None:
             raise exceptions.ProviderNotRegisteredError(
                 provider_type=dependency_type,
-                suggestions=suggester.suggest(dependency_type, self.providers_registry),
+                suggestions=suggester.suggest(dependency_type, registry),
             )
-
-        return self.resolve_provider(provider)
+        if self.closed:
+            self._prepare()
+        try:
+            resolver = registry._resolvers.get(provider.provider_id)  # noqa: SLF001
+            if resolver is None:
+                resolver = registry.resolver_for(provider)
+            return resolver(self)
+        except RecursionError as exc:
+            _handle_recursion_error(provider, self, exc)
 
     def resolve_dependency(self, dependency: "AbstractProvider[types.T] | type[types.T]") -> types.T:
         """Resolve a provider reference or a type — the marker-dispatch entry point for integrations.
@@ -213,7 +226,10 @@ def resolve_dependency(self, dependency: "AbstractProvider[types.T] | type[types
         return self.resolve(dependency)
 
     def resolve_provider(self, provider: "AbstractProvider[types.T]") -> types.T:
-        """Resolve a specific provider by reference via its compiled resolver."""
+        """Resolve a specific provider by reference via its compiled resolver.
+
+        `resolve` holds a copy of this body; any change here belongs there too.
+        """
         if self.closed:
             self._prepare()
         try:

planning/decisions/2026-08-03-resolve-provider-not-a-seam.md

@@ -0,0 +1,76 @@
+---
+summary: `resolve_provider` is not an interception seam and `Container` subclassing is not a supported way to intercept resolution — since the compiled resolvers landed it has only ever seen top-level calls, so inlining it into `resolve()` narrows nothing that worked.
+---
+
+# `resolve_provider` is not an interception seam
+
+**Decision:** `Container.resolve_provider` is an entry point, not a hook. Overriding
+it in a `Container` subclass is not a supported way to observe or intercept
+resolution, and the resolve path is free to bypass it. This licenses inlining its
+body into `Container.resolve`. `find_container` is **not** affected and remains a
+blessed extension point.
+
+## Context
+
+Inlining `find_provider` + `resolve_provider` into `Container.resolve` measures
+**-19% (~38 ns) on every by-type resolve** — the path every `@inject` marker and
+framework integration takes. It was deferred partly because the same structural
+objection that killed
+[`2026-08-01-scope-map-inline-declined.md`](2026-08-01-scope-map-inline-declined.md)
+appears to apply: `resolve_provider` is a public method on a subclassable class,
+and `Container.__init__` builds children via `self.__class__`, so a subclass rides
+the whole tree. Bypassing it would mean a subclass's override no longer runs for
+by-type calls.
+
+## Decision & rationale
+
+**It is already not a seam, and that is measurable rather than arguable.** Since
+the compiled resolvers shipped in 2.29.0, a resolver calls its dependencies'
+resolvers *directly*; nothing routes a nested node through `resolve_provider`. Its
+only callers are `resolve()`, `resolve_dependency()`, and the cycle back-edge
+thunk in `ProvidersRegistry.resolver_for`. Demonstrated on `main` before this
+change: a `Container` subclass overriding `resolve_provider` and resolving a
+**4-node chain** records exactly **1** call — the top-level one. An override has
+never seen the graph. Inlining removes one of the three top-level call sites; the
+by-reference and marker-dispatch entries still route through it.
+
+So the thing the objection protects does not exist. What a subclass can still do
+after this change is instrument the *entry points* by overriding `resolve` and
+`resolve_provider` — which is what someone wanting that would actually reach for,
+and it keeps working.
+
+**This is deliberately narrower than the `_scope_map` ruling, which stands.**
+`find_container` is consulted on every cross-scope hop, and the container it
+returns owns the cached instance and runs its finalizer — bypassing an override
+there silently relocates lifecycle ownership, which is a bug, not a missed hook.
+`resolve_provider` has no such consequence: bypassing an override loses
+observation, not correctness. The two are not the same call and are not being
+ruled on together.
+
+**Field check.** An audit of all 13 sibling integration wheels found zero
+`Container` subclasses and zero `resolve_provider` overrides. `Container`
+subclassing is not documented as an extension point anywhere in `architecture/` or
+`docs/`.
+
+**Accepted costs**, disclosed rather than discovered later:
+
+- A genuinely duplicated ~8-line body (closed check, memo hit, `resolver_for`
+  fallback, resolver call, `RecursionError` conversion) now lives in both `resolve`
+  and `resolve_provider` and must be edited in lockstep. This is the real price and
+  it is permanent.
+- An exception raised through `resolve()` loses one traceback frame (5 → 4;
+  `resolve_provider` no longer appears). Verified directly.
+- Recursion headroom moves by one frame in the benign direction.
+
+**Consequence worth naming.** Together with
+[`2026-07-30-debug-resolution-tracing-declined.md`](2026-07-30-debug-resolution-tracing-declined.md),
+modern-di offers no built-in way to observe *per-node* resolution. That was already
+true — the compiled resolvers removed the last interior call — and this decision
+records it rather than creating it. Entry-point instrumentation remains available
+by overriding both public entry methods.
+
+## Revisit trigger
+
+A concrete request for per-resolve interception from a real integration or user.
+The answer then is a designed seam with a stated contract — not a re-blessing of
+subclass overrides, which the compiled resolve path stopped honouring in 2.29.0.

tests/test_runtime_cycle_guard.py

@@ -220,3 +220,43 @@ class G(Group):
         pytest.fail("expected CircularDependencyError")
     finally:  # pragma: no cover
         sys.setrecursionlimit(limit)
+
+
+def test_by_reference_cycle_raises_circular_dependency_error() -> None:
+    # By-reference twin of the by-type test above, and the only guard on `resolve_provider`'s
+    # own conversion: `Container.resolve` carries a second copy, so replacing the conversion
+    # here with a bare re-raise still passes every by-type cycle test. This is a behavioural
+    # guard, not a coverage one -- the line is covered by
+    # `test_by_reference_recursionerror_passes_through`, which reaches it without an overflow.
+    # Same `except`-clause shape and shallow limit, per `_SHALLOW_RECURSION_LIMIT`.
+    container = Container(groups=[CycleGroup])
+    container.open()
+    original_limit = sys.getrecursionlimit()
+    sys.setrecursionlimit(_SHALLOW_RECURSION_LIMIT)
+    try:
+        container.resolve_provider(CycleGroup.a)
+    except exceptions.CircularDependencyError as exc:  # pragma: no cover
+        _assert_simple_cycle(exc)
+    else:  # pragma: no cover
+        pytest.fail("expected CircularDependencyError")
+    finally:  # pragma: no cover
+        sys.setrecursionlimit(original_limit)
+
+
+def test_by_reference_recursionerror_passes_through() -> None:
+    # Reaches `resolve_provider`'s handler WITHOUT a stack overflow, so the trace function is
+    # still alive and the line is recorded on CPython below 3.12. The by-type twin of this
+    # (`test_validated_graph_reraises_recursionerror_without_walk`) now lands on `resolve`'s
+    # own copy of the handler, leaving this entry point otherwise untraced.
+    class SelfRec:
+        def __init__(self) -> None:
+            raise RecursionError
+
+    class G(Group):
+        s = providers.Factory(scope=Scope.APP, creator=SelfRec)
+
+    container = Container(scope=Scope.APP, groups=[G])
+    container.validate()
+    container.open()
+    with pytest.raises(RecursionError):
+        container.resolve_provider(G.s)