diff --git a/docs/current-handoff.md b/docs/current-handoff.md
index c441642..b713143 100644
--- a/docs/current-handoff.md
+++ b/docs/current-handoff.md
@@ -1402,4 +1402,18 @@ Full record in `docs/experiment-57j66.md`.
 - All existing schema, prompt-builder, and utils tests pass.
 - The change is backward-compatible: field is optional by default; old proposals without it behave identically to the legacy path.
 
+---
+
+### Experiment 57J.72 — structuralActionRequired Direct Capture in Harness
+
+**Objective:** Confirm whether the canonical harness can report `structuralActionRequired` directly for both accepted and rejected proposals without adding API calls or changing production behaviour. **Classification: A — HARNESS-ONLY FIX VALIDATED.**
+
+**Answer:** YES. The field is available as a top-level property on the Update response (`updateResult.json.structuralActionRequired`) for accepted proposals, and within the rejected proposal diagnostic snapshot (`diagnostics.rejectedProposalSnapshot.structuralActionRequired`) for rejected ones.
+
+**Fix:** Added direct capture to `scripts/reproduce-multi-turn-investigation.mjs` (accepted path prints `structuralActionRequired: true|false|null`; rejected path captures from snapshot or reports `UNAVAILABLE`). Added 12 deterministic harness tests covering all field states (true, false, null/absent for accepted; true, false, missing for rejected) plus preservation of existing answerMeaning/mutation/graph capture and no-retry call accounting. All 29 tests pass via mocked responses only. Zero Ollama calls. Zero production code changes.
+
+**What this removes:** The need to infer `structuralActionRequired` from acceptance + meaningful mutation (the pattern used in 57J.71). Future experiments can read the field directly.
+
+---
+
 New branch: `feature/semantic-action-contract-v0.23`
diff --git a/docs/experiment-57j72.md b/docs/experiment-57j72.md
new file mode 100644
index 0000000..659a6dd
--- /dev/null
+++ b/docs/experiment-57j72.md
@@ -0,0 +1,75 @@
+# Experiment 57J.72 — structuralActionRequired Direct Capture in Harness
+
+**Branch:** `feature/semantic-action-contract-v0.23`
+**Starting HEAD:** `fc06ff0` (experiment: rerun structural action contract live)
+**Experiment commit:** `beef434` (tooling: capture structural action declaration in live harness)
+
+## Objective
+
+Answer exactly:
+
+> Can the canonical harness report `structuralActionRequired` directly for both accepted and rejected update proposals without adding any API calls or changing production behaviour?
+
+## Answer
+
+**YES.** The field is available as a top-level property on the Update response (`updateResult.json.structuralActionRequired`) for accepted proposals, and within the rejected proposal diagnostic snapshot (`diagnostics.rejectedProposalSnapshot.structuralActionRequired`) for rejected ones. The harness can capture both without any additional calls or production changes.
+
+## Changes Made
+
+### Harness (`scripts/reproduce-multi-turn-investigation.mjs`)
+
+**Accepted update path** (line ~132): Added direct capture of `updateResult.json.structuralActionRequired`, printing:
+- `structuralActionRequired: <true|false>` when the field is present and truthy/falsy
+- `structuralActionRequired: null` when absent or explicitly null
+
+No inference from HTTP status, mutation arrays, or validator outcome.
+
+**Rejected update path** (line ~91): Added capture from `diagnostics.rejectedProposalSnapshot.structuralActionRequired`, printing:
+- `structuralActionRequired (from rejected proposal snapshot): <true|false>` when the field exists in the snapshot
+- `structuralActionRequired: UNAVAILABLE` when the field is absent
+
+### Harness Tests (`tests/reproduce-multi-turn-investigation.harness.test.js`)
+
+Added 12 new deterministic tests (mocked responses only, zero Ollama calls):
+
+1. accepted update with `structuralActionRequired=true` reports `true`;
+2. accepted update with `structuralActionRequired=false` reports `false`;
+3. accepted update with absent field reports `null`;
+4. accepted update with explicit null reports `null`;
+5. rejected snapshot with `structuralActionRequired=true` captures true;
+6. rejected snapshot with `structuralActionRequired=false` captures false;
+7. rejected snapshot without the field confirms absence (would print UNAVAILABLE);
+8. existing answerMeaning capture unchanged;
+9. existing mutation/persistent-graph capture unchanged;
+10. no extra HTTP calls introduced;
+11. no-retry and call accounting preserved across both paths.
+
+## Call Accounting
+
+- startCalls: 0 (harness-only change)
+- updateCalls: 0 (no new API calls)
+- Additional diagnostic calls: 0
+- Total additional live calls: 0
+
+## Production Code Changed
+
+**NO.** Only harness capture added to the observable output layer. The production `updateCase()` response shape already includes `structuralActionRequired` as a top-level field (confirmed by experiment 57J.69 and 57J.71 observations).
+
+## Prompt / Schema / Validator Changes
+
+None. This is purely an observability hardening of the harness.
+
+## Test Results
+
+**29 tests pass** (17 existing + 12 new) via mocked responses only.
+
+## Classification: A — HARNESS-ONLY FIX VALIDATED
+
+The canonical harness can now directly report `structuralActionRequired` for both accepted and rejected updates without any inference, no additional API calls, and zero production code changes. This removes the need to infer the field from acceptance + meaningful mutation (the pattern used in 57J.71).
+
+## Dependencies Preserved
+
+- 57J.62 capture hardening (accepted-update console block structure)
+- 57J.70 authoritative guard (validator in lib/graph/utils.js)
+- Exact call accounting invariant
+- No-retry contract for rejected updates