Add P1-#6: Capabilities cache TTL invalidation E2E (F3.cache-invalidation)

Summary

• New E2E Listening_ProbePastCacheTtl_RebuildsWithFreshAgentValue pins the OTHER direction of the [CacheResponse(60)] cache contract
• Existing Listening_RepeatedProbes_WithinCacheTtl_ReturnCachedResponse asserts the cache holds within TTL; this PR asserts it expires + rebuilds past TTL
• Catches "cache TTL silently stretched" regressions invisible to the existing within-TTL test

Why this matters

[CacheResponse(60)] is a contract attribute on ICapabilitiesService.GetCapabilities — production server caches the response for 60s to reduce health-check-poll storms.

Test	Direction asserted
Listening_RepeatedProbes_WithinCacheTtl_ReturnCachedResponse	Cache holds within 60s window (returns stale v1 even after agent flips to v2)
Listening_ProbePastCacheTtl_RebuildsWithFreshAgentValue (this PR)	Cache expires + rebuilds past 60s window (returns fresh v2)

Pre-PR untested risk

If cache TTL stretches silently (regression changes [CacheResponse(60)] to [CacheResponse(3600)]):

• Operators would see stale version in UI for an HOUR after every upgrade
• The within-TTL test would still pass (60s contract is a ceiling)
• Only an explicit "wait past 60s + assert refresh" catches it

Test mechanism (~75s)

1. Initial probe at v1 → cached for ≤60s
2. Flip agent to v2 (server cache still has v1)
3. Within-TTL probe → returns CACHED v1 (sanity: cache works)
4. Wait > 60s (production cache TTL) — total wait 65s
5. Post-TTL probe → cache miss → rebuild → returns FRESH v2

Why test runtime is 75s

[CacheResponse(60)] is a wire-contract attribute on ICapabilitiesService.GetCapabilities. Making it configurable for tests would either:

• Change production behaviour (bad)
• Require a test-only contract (violates Rule 12.4 — test would run against a different surface than production)

75s test runtime is the cost of pinning the real production contract.

Test plan

• dotnet build — 0 errors
• CI on windows-latest runs Category=TentacleCapabilitiesE2E:
  • Listening_ProbePastCacheTtl_RebuildsWithFreshAgentValue passes (~75s)
  • All other capabilities tests still green

Phase status — P0/P1 sweep complete after this lands

PR	Priority	Title	Status
#275	P0-#3	LocalScriptService async-flush	🟡 CI
#276	P0-#1	SCM-launched real-binary E2E	🟡 CI
#277	P0-#2	Server-restart polling-reconnect E2E	🟡 CI
#278	P1-#4	Upgrade + polling composite E2E	🟡 CI
#279	P1-#5	Long-soak with leak detection	🟡 CI
this	P1-#6	Capabilities cache TTL invalidation	🟡 CI pending

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