experiment: audit behaviour reachability and blocking

docs/design-evolution-log.md

@@ -2324,3 +2324,83 @@ Pending Rob's review. Five behaviours are too narrow for this to be definitive,
 - `docs/current-handoff.md` — return-to-work note replaced
 
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+
+## Experiment 40 — Audit Behaviour Reachability and Blocking (2026-08-06)
+
+### Objective
+
+Why did Clarify, Summarise, and Pause not appear during Experiment 39? Acknowledge: 5 (71%), Continue: 2 (29%), others: 0. This is a passive diagnostic — no rule changes, no engine modifications.
+
+### Method
+
+One test file (`tests/behaviour-selection.reachability.test.js`) containing:
+- Diagnostic audit helper that evaluates every behaviour rule against one assessment object
+- Real-scenario audits across the same Experiment 39 turns (8 turns total)
+- Synthetic reachability checks for each behaviour in isolation
+
+### Findings
+
+#### Summarise — eligible_but_blocked
+
+Eligible in 2 of 7 real turns:
+- long-investigation turn 1 (resolvedNodeCount ≥ 3 + progress=steady triggers summarise rule)
+- long-investigation turn 2 (phase=concluding triggers summarise rule)
+
+In both cases, health=healthy simultaneously, so Acknowledge (priority 1) fires first. Summarise rules are met but its output is never returned because the selector returns early on priority ordering.
+
+**Root cause: priority conflict, not assessor failure.** The phase evidence correctly identifies concluding/synthesising states; the problem is that Acknowledge's broader trigger condition (health=healthy is the most common state) fires first.
+
+#### Clarify — never_eligible_in_tested_scenarios (reachable only in synthetic case)
+
+Not eligible in any of 7 real turns because neither trigger condition is met:
+- `health=too_broad`: requires activeUnknownCount > 3 AND resolvedNodeCount < 2 — no fixture reaches this state
+- `phase=orienting + observationDensity < 3`: current assessor never produces phase=orienting for tested scenarios
+
+Synthetic case confirms the rule fires correctly in isolation (with low-confidence phase to avoid Acknowledge blocking).
+
+**Root cause: assessor health classification logic produces too few `too_broad` cases. The trigger condition is extremely narrow — needs activeUnknownCount > 3 AND resolved < 2 simultaneously.**
+
+#### Pause — eligible_but_blocked
+
+Eligible in 1 of 7 real turns:
+- contradictory-evidence turn 1 (phase=focusing + progress=stalled triggers pause rule)
+
+In this case, health=healthy simultaneously, so Acknowledge blocks it. The second pause trigger (`health=user_overloaded`) is never met because the assessor never produces that state.
+
+**Root cause: same priority conflict as Summarise. One of two rules fires in real data but gets blocked by Acknowledge's earlier position.**
+
+### Synthetic Reachability Confirmation
+
+All five behaviours are independently reachable when isolated from Acknowledge:
+- ✅ acknowledge — healthy + confident phase
+- ✅ clarify — too_broad health (with low-confidence phase to avoid Acknowledge)
+- ✅ summarise — synthesising/concluding phase (without healthy health)
+- ✅ pause — focusing+stalled or user_overloaded (without healthy health)
+- ✅ continue — no rules match
+
+### Classifications
+
+| Behaviour | Classification | Primary Cause |
+|---|---|---|
+| Summarise | eligible_but_blocked | Acknowledge priority 1 fires first when health=healthy |
+| Clarify | never_eligible_in_tested_scenarios (reachable only in synthetic) | `too_broad` trigger too narrow for test scenarios; `orienting+low obs` not produced by assessor |
+| Pause | eligible_but_blocked | Acknowledge priority 1 fires first when health=healthy; `user_overloaded` never produced |
+
+### Impact on Prior Finding (Exp 39)
+
+Experiment 39 concluded "the Acknowledge→Summarise priority conflict prevents Summarise from firing." Experiment 40 confirms this and adds that **Pause faces the same blocking** (1 eligible turn, blocked). Clarify's absence is fundamentally different: its rules are not triggered at all in tested scenarios.
+
+This means any fix must address two distinct problems:
+1. Priority conflict affecting Summarise AND Pause (same cause)
+2. Narrow trigger conditions for Clarify and the `user_overloaded` health state
+
+### Test Results
+
+- `tests/behaviour-selection.reachability.test.js`: 33 passed (new diagnostic file)
+- `tests/behaviour-selection.test.js`: 51 passed (no regressions)
+- `tests/behaviour-selection.real-assessment.test.js`: 16 passed (shared fixtures intact)
+- `tests/investigation-state-assessor.test.js`: 51 passed (assessor unchanged)
+
+### Documents Updated
+- `docs/design-evolution-log.md` — this entry
+- `docs/current-handoff.md` — return-to-work note replaced