test(evals): scope-gate assertion carries its evidence tail; file the detector-flake TODO

The plan-design-review member fails ONLY scopeGateQuestionObserved
intermittently on unchanged code (PR #2593: red rounds 3/11 + rerun,
green rounds 5/6 — every attempt terminal, no plan-mode leak), and a
bare Expected-true/Received-false is undiagnosable from CI logs. The
check now throws with the last-2KB visible evidence, so the next
failure distinguishes a detector-sensitivity miss from a real silent
bypass. TODO filed with the full receipt trail.

TODOS.md

@@ -2418,6 +2418,22 @@ by shard parallelism; the per-file wall cost remains.
 **Where:** test/gstack-gbrain-detect-mcp-mode.test.ts.
 **Effort:** S (human ~2h, CC ~15min).
 
+### P2: plan-design-review scope-gate detector is marginal under CI contention
+
+**What:** `plan-design-review reaches a terminal outcome outside plan mode`
+(test/skill-e2e-plan-mode-no-op.test.ts) intermittently fails ONLY the
+`scopeGateQuestionObserved` check on unchanged code — PR #2593 CI: failed
+rounds 3/11 + one rerun, passed rounds 5/6, all attempts reaching a terminal
+outcome with no plan-mode leak. Hypothesis: the PTY detector anchors on a
+render shape that scrolls out or gets rephrased under 40-way in-shard
+contention. The assertion now throws WITH the last-2KB evidence tail, so the
+next CI failure carries the screen contents; fix the detector (scan full
+scrollback, or widen the anchored shape) from that data.
+
+**Where:** test/helpers/claude-pty-runner.ts (scopeGateQuestionObserved
+detector), test/skill-e2e-plan-mode-no-op.test.ts.
+**Effort:** S (human ~3h, CC ~20min + one CI round with evidence).
+
 ### P3: Diagnose the browser-manager-unit wedge on windows-latest
 
 **What:** The expanded Windows lane wedges to its wall deadline inside

test/skill-e2e-plan-mode-no-op.test.ts

@@ -99,7 +99,21 @@ describeE2E('plan-mode-info no-op outside plan mode (gate regression)', () => {
         // outcome === 'asked' would let a silent-bypass run that reaches
         // plan_ready (isPlanReadyVisible also matches common prose) sail
         // through — the exact regression this test exists to catch.
-        expect(obs.scopeGateQuestionObserved ?? false).toBe(true);
+        //
+        // Throw WITH the evidence tail instead of a bare expect: this member
+        // (plan-design-review especially) intermittently fails ONLY this
+        // check on unchanged code (PR #2593 rounds 3/11/rerun, passing
+        // rounds 5/6), and a bare Expected-true/Received-false in CI logs is
+        // undiagnosable — we can't tell a detector-sensitivity miss (render
+        // shape scrolled/rephrased) from a real silent bypass without seeing
+        // what the screen held.
+        if (!(obs.scopeGateQuestionObserved ?? false)) {
+          throw new Error(
+            `scope-gate question NOT observed (${skillName}): outcome=${obs.outcome}\n` +
+              `elapsed: ${obs.elapsedMs}ms\n` +
+              `--- evidence (last 2KB visible) ---\n${obs.evidence}`,
+          );
+        }
       }
     }, 360_000);
   }