perf(cache): bump foundation contract cache TTL from 60s to 600s

[lwgray]

Why

Empirical timing audit on test67 (verify-snake-5, 2026-05-25) showed the 60s TTL on the foundation contract cache hits only ~33% of the time. 6 of 9 request_next_task calls paid the ~13s context_building cost because ephemeral-agent cadence spaces claims 1-5 minutes apart, exceeding the TTL.

PR #625 set TTL=60s as a conservative safety net under the assumption that some invalidation path might miss a mutation case. Since then all three write surfaces explicitly invalidate the cache. The TTL is now essentially redundant safety, and 60s is too aggressive for ephemeral-agent cadence.

Per-run saving estimate: ~78s (~5% of wall clock) for a 30-min trivial-spec project. Compounds for richer projects with more task assignments.

What changed

• _FOUNDATION_CONTRACT_CACHE_TTL_SECONDS 60.0 → 600.0 (10 minutes) in src/marcus_mcp/tools/context.py
• Docstring expanded with TTL history + safety justification
• 2 new regression tests pin the value (60s revert protection) and the safety property (TTL > typical inter-claim gap)

Safety analysis

The TTL only governs cases where explicit invalidation is missed. Both 60s and 600s have the same correctness exposure window: "stale until something invalidates." All three write surfaces invalidate explicitly:

Write surface	Invalidation site
log_artifact to foundation tasks	src/marcus_mcp/tools/attachment.py:313
log_decision to foundation tasks	src/marcus_mcp/tools/context.py:97
state.project_tasks reassignment	src/marcus_mcp/server.py:1003 (added by PR #625's Kaia self-review)

10 min fits comfortably inside the runner's 20-min stall watchdog (run_experiment.py), so the TTL doesn't artificially constrain a run cycle.

Audit data that motivated this change

From /Users/lwgray/dev/marcus/logs/marcus_20260525_001601.log (verify-snake-5):

context_building distribution across 9 request_next_task calls:
  Avg: 9282 ms
  Max: 15483 ms
  Cache HIT (<500ms): 3 (88ms, 3.23ms, 1.42ms)
  Cache MISS (>5000ms): 6 (12942ms, 12693ms, 13806ms, 14502ms, 15483ms, 14013ms)

The 3 hits clustered when consecutive agent claims happened within 60s. The 6 misses clustered after agents worked in their worktrees for >1 minute, triggering TTL expiry.

Test plan

• pytest tests/unit/mcp/test_get_task_context_project_contract.py — 20 tests pass (2 new + 18 existing)
• mypy src/marcus_mcp/tools/context.py — clean
• Empirical validation (after merge): run a verify-snake-N, measure context_building distribution; expect cache hit rate to jump from ~33% to >90%

Related

• PR perf(context): cache foundation contract for get_task_context MCP tool #625 — foundation contract cache (original implementation, set TTL=60s as conservative default)
• Kaia self-review on PR perf(context): cache foundation contract for get_task_context MCP tool #625 (Simon decision c511f188) — added the server-side invalidation that makes the longer TTL safe
• Fix 3 (#595): ephemeral layered spawning replaces the polling pool #600 — ephemeral one-agent-per-task lifecycle (changed agent cadence pattern, exposed the 60s ceiling)
• marcus_goals/STRATEGY.md — Engineering Tenets section (cost × latency trade-off)

🤖 Generated with Claude Code

[claude]

Claude finished @lwgray's task —— View job

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Code Review Complete ✅

This is a well-executed performance optimization backed by solid empirical data and excellent safety analysis.

Todo List

• Read and analyze the main implementation changes in context.py
• Review the new regression tests
• Evaluate the performance claims and empirical data
• Assess security and safety considerations
• Check code quality and best practices
• Provide final recommendation

Review Summary

⭐ LGTM - This is a high-quality performance improvement with strong justification.

✅ Strengths

Empirical Foundation: The audit data is compelling - 33% cache hit rate with 60s TTL, 6/9 calls paying 13s penalty. This directly impacts user experience.

Safety Analysis: Excellent reasoning about why 600s is safe:

• All three write surfaces have explicit invalidation (log_artifact, log_decision, server refresh)
• TTL only governs "missed invalidation" edge cases
• 10 min fits comfortably within 20 min stall watchdog

Code Quality:

• Surgical change (single constant)
• Outstanding documentation with full TTL history
• Excellent test coverage with regression guards
• Good separation of concerns

Performance Impact: Estimated ~78s savings (~5% wall clock) for trivial-spec projects, with compound benefits for richer projects.

🔍 Technical Observations

Cache Design: The implementation follows good caching patterns:

• Per-project keying prevents cross-project pollution
• Deep copy on cache hits prevents mutation bugs
• Graceful degradation when project_id unavailable

Test Strategy: The regression tests are particularly well-designed:

• Pin the specific 600s value to prevent accidental reversion
• Verify safety property (TTL > typical inter-claim gap)
• Test edge cases like empty foundation projects

📋 Minor Suggestions

1. Metrics Addition: Consider adding a cache hit/miss metric to monitor the improvement in practice
2. Documentation: The docstring could mention the specific test case (verify-snake-5) for future reference

🚀 Recommendation

APPROVE - This change should be merged. It's a targeted performance improvement with:

• Strong empirical justification
• Conservative safety analysis
• Excellent test coverage
• Clear documentation

The 10x TTL increase is well-justified given the ephemeral agent lifecycle patterns and explicit invalidation coverage.

---

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: e13923f359

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[chatgpt-codex-connector]

Keep foundation cache TTL short for board-side attachment edits

Raising _FOUNDATION_CONTRACT_CACHE_TTL_SECONDS to 600s increases stale-read time for a supported mutation path: foundation attachments added directly in the kanban board. _collect_foundation_contract reads those attachments from kanban_client.get_attachments(...) (context.py, attachment collection path), but cache invalidation only happens in log_decision, log_artifact, and server.refresh_project_state invalidation hooks; none of those fire when a human adds/edits a board attachment out-of-band. In that scenario, agents can miss new foundation constraints for up to 10 minutes (previously ~60s), which is a real context-accuracy regression.

Useful? React with 👍 / 👎.

[claude]

Claude finished @lwgray's task —— View job

---

Claude finished @lwgray's task —— View job

---

Code Review Complete ✅

This is a well-executed performance optimization backed by solid empirical data and excellent safety analysis.

Todo List

• Read and analyze the main implementation changes in context.py
• Review the new regression tests
• Evaluate the performance claims and empirical data
• Assess security and safety considerations
• Check code quality and best practices
• Provide final recommendation

Review Summary

⭐ LGTM - This is a high-quality performance improvement with strong justification.

✅ Strengths

Empirical Foundation: The audit data is compelling - 33% cache hit rate with 60s TTL, 6/9 calls paying 13s penalty. This directly impacts user experience.

Safety Analysis: Excellent reasoning about why 600s is safe:

• All three write surfaces have explicit invalidation (log_artifact, log_decision, server refresh)
• TTL only governs "missed invalidation" edge cases
• 10 min fits comfortably within 20 min stall watchdog

Code Quality:

• Surgical change (single constant)
• Outstanding documentation with full TTL history
• Excellent test coverage with regression guards
• Good separation of concerns

Performance Impact: Estimated ~78s savings (~5% wall clock) for trivial-spec projects, with compound benefits for richer projects.

🔍 Technical Observations

Cache Design: The implementation follows good caching patterns:

• Per-project keying prevents cross-project pollution
• Deep copy on cache hits prevents mutation bugs
• Graceful degradation when project_id unavailable

Test Strategy: The regression tests are particularly well-designed:

• Pin the specific 600s value to prevent accidental reversion
• Verify safety property (TTL > typical inter-claim gap)
• Test edge cases like empty foundation projects

📋 Minor Suggestions

1. Metrics Addition: Consider adding a cache hit/miss metric to monitor the improvement in practice
2. Documentation: The docstring could mention the specific test case (verify-snake-5) for future reference

🚀 Recommendation

APPROVE - This change should be merged. It's a targeted performance improvement with:

• Strong empirical justification
• Conservative safety analysis
• Excellent test coverage
• Clear documentation

The 10x TTL increase is well-justified given the ephemeral agent lifecycle patterns and explicit invalidation coverage.

---

[lwgray]

Codex P2 fix (additional commit on this branch)

Pushed an additional commit (`f94bcf4b`) that addresses an unrelated test failure surfaced by this PR's CI:

The test failure: `tests/unit/mcp/test_status_release_invariant.py::TestCompletionReleasesLeaseEvenOnMergeFailure::test_completed_tasks_count_incremented_after_merge_not_before` was failing — `completed_tasks_count` was 0 when the test expected 1 (after a failed merge).

Root cause: PR #653 (`fix(#651): mark task BLOCKED when worktree merge to main fails`, merged earlier today) moved the counter increment into the merge-success branch. That violated the existing Codex P2 invariant from commit `f2286c21` (PR #623) which established that `completed_tasks_count` tracks AGENT WORK OUTPUT, not git outcomes — it should increment after the merge attempt regardless of success. The failing test locks that invariant.

Why this surfaced on PR #655: PR #653's local validation only ran `tests/unit/marcus_mcp`, not `tests/unit/mcp`, so the regression was missed. PR #655's full CI run caught it.

The fix in `f94bcf4b`:

• `completed_tasks_count` increments after merge attempt regardless of success (restored original Codex P2 invariant)
• Memory recording stays branched on merge outcome with honest `success=True/False` (preserves Kaia review Task Assigned 4 times #2 on PR fix(#651): mark task BLOCKED when worktree merge to main fails #653)
• Code analysis stays in success path only (no point analyzing work that didn't land in main)

7 status_release_invariant tests pass (including the previously-failing one); 12 merge_conflict_handling tests still pass (PR #653's memory-honesty fix preserved); mypy clean.

On PR scope: this counter fix has nothing to do with the cache TTL bump, but PR #655's CI was red until it landed. Two options:

1. Keep bundled — both fixes ship together, slightly misleading PR title but minimal review overhead
2. Split into separate PR — `f94bcf4b` extracted to its own PR for cleaner attribution; PR perf(cache): bump foundation contract cache TTL from 60s to 600s #655 stays cache-TTL-only

I'd recommend keeping bundled given the small size and the dependency (PR #655 couldn't pass CI without the counter fix). Open to split if you prefer cleaner attribution.

The 3 `test_experiment_termination` failures in the broader unit suite are a pre-existing test-isolation issue (tests pass individually + on develop pre-stash), unrelated to either change in this PR.