fix(search): refuse overlapping Search retirement runs with a session lock

[waleedlatif1]

Summary

This follows up on #8522 and addresses its Greptile finding, "Plain runs lack the documented lock".

The operator command's plain retirement run took no lock. The runbook says it holds a session advisory lock. Two overlapping runs could not corrupt progress, because every page locks the progress row, but they would double the load on the primary.

Retirement now takes a session try-lock (search-embedding-retirement), the same pattern maintenance already uses (0028). It refuses to start while another run holds the lock, and it releases the lock in finally.

Behaviour changes

• A second concurrent retirement run fails at once with "Search retirement is already running" and touches nothing.
• A single run is unchanged.

Test plan

• New real-Postgres test: another session holds the lock, the run rejects and creates no cleanup tables, then a run without the competing lock completes. The test failed before the fix ("promise resolved instead of rejecting").
• The lock-retry test now has the suite's 60 s timeout. Under the gentler default pacing, its lock wait (~1.5 s) is followed by a pause twice as long, which overran the default 5 s timeout when the whole suite ran in parallel. The full packages/db integration suite then passed 129/129 three times in a row.
• Lint, the packages/db type-check and bun run check:audits pass.

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Project	Deployment	Actions	Updated
docs	Ready	Preview	Oct 1, 2026 5:38pm UTC

[waleedlatif1]

@greptile

[waleedlatif1]

@cubic-dev-ai review this PR

[cubic-dev-ai]

@cubic-dev-ai review this PR

@waleedlatif1 I have started the AI code review. It will take a few minutes to complete.

[greptile-apps]

Confidence Score: 5/5

[High risk] Adds session lock to prevent concurrent search retirement runs.

No new actionable issue prevents merging under this review.

Summary

The PR adds a session advisory lock to plain Search embedding retirement, tests rejection when another session holds it, extends one integration-test timeout, and updates the runbook.

_{Reviews (2) · Last reviewed commit: "fix(search): refuse overlapping Search r..."}

[cubic-dev-ai]

All reported issues were addressed across 3 files

<sub>Reply with feedback, questions, or to request a fix.

Fix all with cubic | Re-trigger cubic</sub>

[cubic-dev-ai]

All reported issues were addressed across 3 files

<sub>Requires human review: Auto-approval blocked because this review re-detected 1 unresolved issue already reported by Cubic.

Re-trigger cubic</sub>

[waleedlatif1]

@greptile

[waleedlatif1]

@cubic-dev-ai review this PR

[cubic-dev-ai]

@cubic-dev-ai review this PR

@waleedlatif1 I have started the AI code review. It will take a few minutes to complete.

[cubic-dev-ai]

No issues found across 3 files

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Re-trigger cubic}