diff --git a/internal/attractor/agents/tmux_env_test.go b/internal/attractor/agents/tmux_env_test.go
new file mode 100644
index 00000000..37320238
--- /dev/null
+++ b/internal/attractor/agents/tmux_env_test.go
@@ -0,0 +1,68 @@
+// Unit tests for the tmux agent session env-building helper.
+package agents
+
+import (
+	"testing"
+
+	"github.com/danshapiro/kilroy/internal/attractor/agents/templates"
+	"github.com/danshapiro/kilroy/internal/attractor/engine"
+)
+
+func TestBuildTmuxAgentEnv_IncludesStageStatusContractAndRuntime(t *testing.T) {
+	tmpl := &templates.Template{
+		BuildEnv: func() map[string]string {
+			return map[string]string{"TOOL_DEFAULT": "present"}
+		},
+	}
+	workDir := t.TempDir()
+	logsRoot := t.TempDir()
+	execCtx := &engine.Execution{
+		WorktreeDir: workDir,
+		LogsRoot:    logsRoot,
+		Engine: &engine.Engine{
+			Options: engine.RunOptions{RunID: "run-001"},
+		},
+	}
+
+	env := buildTmuxAgentEnv(tmpl, execCtx, "node-alpha")
+
+	cases := map[string]string{
+		"TOOL_DEFAULT":        "present",
+		"KILROY_RUN_ID":       "run-001",
+		"KILROY_NODE_ID":      "node-alpha",
+		"KILROY_WORKTREE_DIR": workDir,
+		"KILROY_LOGS_ROOT":    logsRoot,
+	}
+	for k, want := range cases {
+		if got := env[k]; got != want {
+			t.Errorf("%s = %q, want %q", k, got, want)
+		}
+	}
+	if env["KILROY_STAGE_STATUS_PATH"] == "" {
+		t.Error("KILROY_STAGE_STATUS_PATH missing — agents cannot find where to write status.json")
+	}
+	if env["KILROY_STAGE_STATUS_FALLBACK_PATH"] == "" {
+		t.Error("KILROY_STAGE_STATUS_FALLBACK_PATH missing")
+	}
+	if env["KILROY_STAGE_LOGS_DIR"] == "" {
+		t.Error("KILROY_STAGE_LOGS_DIR missing")
+	}
+	if env["KILROY_DATA_DIR"] == "" {
+		t.Error("KILROY_DATA_DIR missing")
+	}
+}
+
+func TestBuildTmuxAgentEnv_NilTemplateStartsClean(t *testing.T) {
+	execCtx := &engine.Execution{
+		WorktreeDir: t.TempDir(),
+		LogsRoot:    t.TempDir(),
+		Engine:      &engine.Engine{Options: engine.RunOptions{RunID: "run-nil-tmpl"}},
+	}
+	env := buildTmuxAgentEnv(nil, execCtx, "node")
+	if env == nil {
+		t.Fatal("env must not be nil even when template is nil")
+	}
+	if env["KILROY_RUN_ID"] != "run-nil-tmpl" {
+		t.Errorf("KILROY_RUN_ID = %q, want run-nil-tmpl", env["KILROY_RUN_ID"])
+	}
+}
diff --git a/internal/attractor/agents/tmux_handler.go b/internal/attractor/agents/tmux_handler.go
index 54727a67..30fd4a62 100644
--- a/internal/attractor/agents/tmux_handler.go
+++ b/internal/attractor/agents/tmux_handler.go
@@ -69,20 +69,7 @@ func (h *TmuxAgentHandler) Execute(ctx context.Context, exec *engine.Execution,
 	sessionName := buildSessionName(runID, node.ID)
 
 	// Build environment variables.
-	env := tmpl.BuildEnv()
-	if env == nil {
-		env = map[string]string{}
-	}
-	if runID != "" {
-		env["KILROY_RUN_ID"] = runID
-	}
-	env["KILROY_NODE_ID"] = node.ID
-	// Add input env vars if available.
-	if exec != nil && exec.Engine != nil {
-		for k, v := range engine.InputEnvVars(exec.Engine.Options.Inputs) {
-			env[k] = v
-		}
-	}
+	env := buildTmuxAgentEnv(tmpl, exec, node.ID)
 
 	// Resolve model from node attributes.
 	modelID := strings.TrimSpace(node.Attr("llm_model", ""))
@@ -348,6 +335,31 @@ func resolveToolName(node *model.Node) string {
 	return "claude" // default
 }
 
+// buildTmuxAgentEnv constructs the environment variables passed to a tmux-run
+// agent session. It consolidates the tool template's defaults with the engine
+// runtime invariants (run/node IDs, worktree/logs paths, input env) and the
+// stage status contract paths so the engine-injected status-contract preamble
+// is actionable from inside the session. Without the status contract env vars,
+// agents spend tool calls hunting for KILROY_STAGE_STATUS_PATH.
+func buildTmuxAgentEnv(tmpl *templates.Template, exec *engine.Execution, nodeID string) map[string]string {
+	var env map[string]string
+	if tmpl != nil {
+		env = tmpl.BuildEnv()
+	}
+	if env == nil {
+		env = map[string]string{}
+	}
+	for k, v := range engine.BuildStageRuntimeEnv(exec, nodeID) {
+		env[k] = v
+	}
+	if exec != nil {
+		for k, v := range engine.BuildStageStatusContract(exec.WorktreeDir).EnvVars {
+			env[k] = v
+		}
+	}
+	return env
+}
+
 // buildSessionName creates a unique tmux session name for a node execution.
 func buildSessionName(runID, nodeID string) string {
 	name := "kilroy"
diff --git a/workflows/coding-loop/README.md b/workflows/coding-loop/README.md
new file mode 100644
index 00000000..b56bd11c
--- /dev/null
+++ b/workflows/coding-loop/README.md
@@ -0,0 +1,47 @@
+# coding-loop
+
+An iterative coding workflow that repeatedly chooses sub-tasks, implements them, reviews the results, and decides when the spec is complete.
+
+## What it does
+
+Runs up to 8 loops of:
+
+1. **Task Chooser** — reads the spec + latest review, picks the highest-priority unimplemented sub-task, writes `.kilroy/task.md`.
+2. **Implementer** — reads the task, writes code, commits.
+3. **Reviewer** — diffs HEAD~1..HEAD against the spec, writes `.reviews/iter-NNN.md` and `.reviews/latest.md`, commits.
+4. **Done Gate** — reads spec + latest review, writes `COMPLETE` or `CONTINUE` to `.kilroy/decision.md`.
+
+When Done Gate writes `COMPLETE` (or `loop_max=8` is reached), the loop exits and a **Report** node writes `result.md`.
+
+## How to launch
+
+```bash
+kilroy attractor run \
+  --package workflows/coding-loop/ \
+  --workspace /abs/path/to/target-repo \
+  --input '{"spec":"/abs/path/to/spec.md"}'
+```
+
+- `--workspace` — the repo being coded against (must already exist; the caller handles `git init` / `go mod init` etc.)
+- `--input spec` — absolute path to the spec/requirements file (read in-place; not copied into the repo)
+
+## Input contract
+
+| Key    | Required | Description |
+|--------|----------|-------------|
+| `spec` | yes      | Absolute path to the spec/requirements markdown file |
+
+## Output contract
+
+| File             | Description |
+|------------------|-------------|
+| `result.md`      | Summary: what was implemented, iterations run, final status |
+| `.reviews/iter-NNN.md` | Per-iteration reviewer feedback (committed to repo) |
+| `.reviews/latest.md`   | Rolling copy of the most recent review |
+
+## Known limits
+
+- `loop_max=8` — hard ceiling; if the done-gate never writes `COMPLETE` after 8 iterations, the run fails.
+- Chooser and done-gate use `claude-haiku-4.5` (cheap, API-based). Implementer and reviewer use `claude-sonnet-4.6` (Claude Code CLI via tmux, or API).
+- Spec is NOT committed to the target repo — it is read in-place via the `spec` input path.
+- No pre-flight scaffolding — the caller must initialize the repo before launching.
diff --git a/workflows/coding-loop/graph.dot b/workflows/coding-loop/graph.dot
new file mode 100644
index 00000000..ae1c80a2
--- /dev/null
+++ b/workflows/coding-loop/graph.dot
@@ -0,0 +1,206 @@
+// coding-loop: iterative coding agent with reviewer feedback and LLM done-gate.
+//
+// Inputs: spec (absolute path to a spec file).
+// Output: result.md at the workspace root.
+//
+// Flow (up to loop_max=8 iterations):
+//   start → loop_begin → task_chooser → implementer → reviewer → done_gate → loop_end → report → done
+//
+// Termination: done_gate writes COMPLETE or CONTINUE to .kilroy/decision.md.
+// loop_end checks for COMPLETE and either loops back to loop_begin or exits.
+
+digraph coding_loop {
+    graph [
+        inputs="spec",
+        outputs="result.md",
+        model_stylesheet="
+            * { llm_provider: anthropic; llm_model: claude-haiku-4.5; }
+            .implementer { llm_model: claude-sonnet-4.6; }
+            .reviewer { llm_model: claude-sonnet-4.6; }
+        "
+    ]
+
+    start [shape=Mdiamond, label="Start"]
+    done  [shape=Msquare,  label="Done"]
+
+    // Loop sentinel: marks the top of the iteration scope.
+    // The engine jumps back here when loop_end decides to continue.
+    loop_begin [
+        shape=trapezium,
+        label="Loop Begin",
+        loop_id="main",
+        loop_max=12,
+        loop_until_file_contains=".kilroy/decision.md:COMPLETE"
+    ]
+
+    // Task chooser: lightweight model reads spec + latest review,
+    // decides the most impactful next sub-task, writes .kilroy/task.md.
+    task_chooser [
+        shape=box,
+        label="Task Chooser",
+        agent_mode="agent_loop",
+        prompt="You are the task chooser in an iterative coding workflow.
+
+Your job: read the spec and latest review, then decide the single most important next sub-task for the implementer to work on this iteration.
+
+Steps:
+1. Read .kilroy/INPUT.md. Find the '## spec' section — it contains the absolute path to the spec file.
+2. Read the spec file at that path.
+3. Run: git log --oneline -10
+4. Run: git status
+5. If .reviews/latest.md exists, read it for prior feedback and what remains incomplete.
+6. Choose EXACTLY ONE smallest-possible self-contained sub-task. Do NOT bundle multiple features into one iteration.
+   - If no code files exist yet, pick ONLY the foundation step (e.g. go.mod bootstrap, or the type + constructor) and STOP there. Do not also implement any features.
+   - If foundation exists, pick the SINGLE smallest unimplemented feature. Not two. Not three. Exactly one.
+   - If all features exist but the reviewer flagged a bug, pick JUST that bug and nothing else.
+   The explicit goal is to force multiple tight iterations. Each iteration should produce the minimum-viable increment — a single method, a single test, a single bugfix.
+7. Write a concise task description to .kilroy/task.md. Include:
+   - What to implement: ONE thing, explicitly and narrowly scoped.
+   - Acceptance criteria for THIS sub-task only (2-4 bullets, focused solely on what's being added this iteration).
+   - Files likely affected (your best guess).
+   - Explicit guardrail line, quoted verbatim: Do NOT implement any other features in this iteration. Stop immediately after the scoped sub-task is complete, even if other unimplemented items are visible in the spec.
+   Keep .kilroy/task.md under 30 lines.
+
+When finished, write {\"status\":\"success\"} to $KILROY_STAGE_STATUS_PATH or $KILROY_STAGE_STATUS_FALLBACK_PATH if that fails."
+    ]
+
+    // Implementer: reads .kilroy/task.md, implements the task, commits.
+    implementer [
+        shape=box,
+        label="Implementer",
+        class="implementer",
+        agent_tool="claude",
+        prompt="You are the implementer in an iterative coding workflow.
+
+Your job: read the task and implement it in the codebase.
+
+Steps:
+1. Read .kilroy/task.md for the current sub-task and its acceptance criteria.
+2. Read .kilroy/INPUT.md to find the spec path ('## spec' section), then read the spec for broader context.
+3. Implement ONLY what .kilroy/task.md asks for. Do NOT implement any other features you see in the spec or guess at next steps — the chooser is responsible for scheduling and will hand you the next sub-task on the next iteration. Stay strictly in your lane.
+4. Write clean, idiomatic code. Make targeted changes — do not refactor unrelated code.
+5. Run any applicable tests or build commands to verify your work does not break existing functionality.
+6. Stage and commit ALL changes with a clear message describing what was done (e.g., 'feat: add X per spec').
+   If there is genuinely nothing to implement (task already done), write a note to .kilroy/implementer-note.md and commit that.
+
+When finished, write {\"status\":\"success\"} to $KILROY_STAGE_STATUS_PATH or $KILROY_STAGE_STATUS_FALLBACK_PATH if that fails."
+    ]
+
+    // Reviewer: reads task + diff, writes .reviews/iter-NNN.md and .reviews/latest.md, commits.
+    reviewer [
+        shape=box,
+        label="Reviewer",
+        class="reviewer",
+        agent_tool="claude",
+        prompt="You are the reviewer in an iterative coding workflow.
+
+Your job: review the latest commit against the spec and record structured feedback.
+
+Steps:
+1. Read .kilroy/task.md to understand what was supposed to be implemented this iteration.
+2. Read .kilroy/INPUT.md to find the spec path ('## spec' section), then read the spec for acceptance criteria.
+3. Run: git log --oneline -5
+4. Run: git show HEAD   (shows the commit message + full diff of the implementer's latest commit; works regardless of commit depth)
+5. Compute the iteration number:
+   mkdir -p .reviews
+   N=$(ls .reviews/iter-*.md 2>/dev/null | wc -l | tr -d ' ')
+   ITER=$((N + 1))
+   PADDED=$(printf '%03d' $ITER)
+6. Write your review to both .reviews/iter-${PADDED}.md AND .reviews/latest.md (overwrite latest.md each time).
+   Review format:
+   ## Iteration ${PADDED}
+   ## What Changed
+   (summary of the diff — what files, what logic)
+   ## Against Spec
+   - Done: (list items completed)
+   - Remaining: (list required items not yet implemented)
+   ## Quality Notes
+   (code quality, edge cases, test coverage observations)
+   ## Recommendation
+   CONTINUE — if required spec items remain unimplemented.
+   COMPLETE — ONLY if ALL required spec items are done and the implementation is correct.
+7. Stage and commit the .reviews/ changes:
+   git add .reviews/
+   git commit -m \"review: iteration ${PADDED} feedback\"
+
+When finished, write {\"status\":\"success\"} to $KILROY_STAGE_STATUS_PATH or $KILROY_STAGE_STATUS_FALLBACK_PATH if that fails."
+    ]
+
+    // Done-gate: lightweight LLM decides COMPLETE vs CONTINUE, writes to .kilroy/decision.md.
+    done_gate [
+        shape=box,
+        label="Done Gate",
+        agent_mode="agent_loop",
+        prompt="You are the done-gate in an iterative coding workflow.
+
+Your job: decide whether the spec is fully implemented based on the latest review.
+
+Steps:
+1. Read .kilroy/INPUT.md to find the spec path ('## spec' section), then read the spec.
+2. Run: ls .reviews/
+3. Read .reviews/latest.md (the most recent review).
+4. Optionally read additional .reviews/iter-NNN.md files if you need more context.
+5. Decide:
+   - COMPLETE: ALL required spec items are implemented and the latest review confirms it.
+   - CONTINUE: Required spec items remain unimplemented or the reviewer says CONTINUE.
+
+CRITICAL: Write EXACTLY one of these two words to .kilroy/decision.md — nothing else, no whitespace, no newline:
+  echo -n COMPLETE > .kilroy/decision.md
+  OR
+  echo -n CONTINUE > .kilroy/decision.md
+
+The engine reads this file byte-by-byte to decide loop termination. Any extra characters (spaces, newlines, punctuation) will prevent termination detection.
+
+When finished, write {\"status\":\"success\"} to $KILROY_STAGE_STATUS_PATH or $KILROY_STAGE_STATUS_FALLBACK_PATH if that fails."
+    ]
+
+    // Loop sentinel: marks the end of the iteration scope.
+    // Checks termination conditions; if not met, jumps back to loop_begin.
+    loop_end [
+        shape=invtrapezium,
+        label="Loop End",
+        loop_id="main",
+        loop_max=12,
+        loop_until_file_contains=".kilroy/decision.md:COMPLETE"
+    ]
+
+    // Report: summarizes all work done, iterations run, final status.
+    report [
+        shape=box,
+        label="Report",
+        agent_mode="agent_loop",
+        prompt="You are the final reporter in an iterative coding workflow.
+
+Your job: write a comprehensive summary of the completed work.
+
+Steps:
+1. Read .kilroy/INPUT.md to find the spec path ('## spec' section), then read the spec.
+2. Read .reviews/latest.md for the final review and recommendation.
+3. Count iterations: ls .reviews/iter-*.md 2>/dev/null | wc -l
+4. Run: git log --oneline -20
+5. Read .kilroy/decision.md to confirm the final decision (COMPLETE or CONTINUE/loop_max exceeded).
+6. Write result.md at the workspace root with these sections:
+   ## Summary
+   What was implemented and how it maps to the spec requirements.
+   ## Iterations
+   How many loops ran and what changed in each (brief, one line per iteration).
+   ## Final Review
+   Key points from .reviews/latest.md.
+   ## Commits
+   List of commits made during this run (from git log).
+   ## Status
+   COMPLETE — all required spec items implemented.
+   OR INCOMPLETE — what remains and why the loop stopped.
+
+When finished, write {\"status\":\"success\"} to $KILROY_STAGE_STATUS_PATH or $KILROY_STAGE_STATUS_FALLBACK_PATH if that fails."
+    ]
+
+    start         -> loop_begin
+    loop_begin    -> task_chooser
+    task_chooser  -> implementer
+    implementer   -> reviewer
+    reviewer      -> done_gate
+    done_gate     -> loop_end
+    loop_end      -> report
+    report        -> done
+}
diff --git a/workflows/coding-loop/workflow.toml b/workflows/coding-loop/workflow.toml
new file mode 100644
index 00000000..e75766fc
--- /dev/null
+++ b/workflows/coding-loop/workflow.toml
@@ -0,0 +1,19 @@
+# Coding-loop workflow: iterative LLM coding agent with reviewer feedback and done-gate.
+# Runs up to 8 choose→implement→review→gate iterations against a user-supplied spec.
+# Usage: kilroy attractor run --package workflows/coding-loop/ \
+#          --workspace <target-repo-dir> \
+#          --input '{"spec":"/abs/path/to/spec.md"}'
+
+name = "coding-loop"
+description = "Iterative coding workflow: a task chooser selects sub-tasks, an implementer codes them, a reviewer scores each iteration, and a done-gate decides when the spec is complete."
+version = "0.1.0"
+
+outputs = ["result.md"]
+
+[[inputs]]
+name = "spec"
+description = "Absolute path to the feature/task spec file that defines what to build."
+required = true
+
+[defaults]
+labels = { workflow = "coding-loop" }