Best possible solution:

Apply the single-pass newest-match lookup to the shared gateway checkpoint getter used before branch/restore, keep ordered list behavior where callers need lists, and add real after-fix proof before merge.

Do we have a high-confidence way to reproduce the issue?

Yes. Source inspection shows sessions.compaction.branch and sessions.compaction.restore call the shared getSessionCompactionCheckpoint helper, which still sorts the full checkpoint list before the optimized accessor mutation runs.

Is this the best way to solve the issue?

No. The accessor scan is a good local step, but the best fix also updates the shared gateway lookup so the normal user-facing branch/restore path avoids the O(n log n) sort.

Full review comments:

• [P2] Optimize the shared checkpoint lookup too — src/config/sessions/session-accessor.ts:1358-1366
  The new scan only runs inside the accessor mutation, but normal sessions.compaction.branch and sessions.compaction.restore already call getSessionCompactionCheckpoint; that helper still sorts via listSessionCompactionCheckpoints(...).find(...). Move the single-pass newest-match lookup to the shared getter or update that helper too so the user-facing path actually avoids the full sort.
  Confidence: 0.86

Overall correctness: patch is incorrect
Overall confidence: 0.86

AGENTS.md: found and applied where relevant.

Codex review notes: model internal, reasoning high; reviewed against ab966c214be0.

Label justifications:

• P3: This is a low-risk internal sessions performance cleanup with no compatibility, security, or migration surface.
• rating: 🧂 unranked krab: Overall readiness is 🧂 unranked krab; proof is 🧂 unranked krab and patch quality is 🦐 gold shrimp.
• status: 📣 needs proof: The PR needs real behavior proof before ClawSweeper can clear the contributor ask. Needs real behavior proof before merge: The PR body lists validation commands only; it needs redacted terminal output, logs, screenshots, recording, or a linked artifact from an after-fix branch/restore run before merge. After adding proof, update the PR body; ClawSweeper should re-review automatically. If it does not, the PR author or someone with repository write access can comment @clawsweeper re-review.

PR surface:

Source +7, Tests +86. Total +93 across 2 files.

What I checked:

• Live PR diff: The patch changes only the accessor-level checkpoint finder and adds an accessor-level test for newest matching checkpoint selection. (src/config/sessions/session-accessor.ts:1358, fc1315f15e16)
• Shared gateway lookup still sorts: Current main's getSessionCompactionCheckpoint calls listSessionCompactionCheckpoints(...).find(...), and the list helper sorts the full checkpoint list by createdAt before filtering by id. (src/gateway/session-compaction-checkpoints.ts:819, ab966c214be0)
• Branch RPC caller: The sessions.compaction.branch handler calls getSessionCompactionCheckpoint before invoking compactionCheckpointStore.branchCheckpointSession, so the user-facing branch path still pays the shared sort first. (src/gateway/server-methods/sessions.ts:1612, ab966c214be0)
• Restore RPC caller: The sessions.compaction.restore handler also calls getSessionCompactionCheckpoint before restoreCheckpointSession, so restore keeps the same pre-mutation sort. (src/gateway/server-methods/sessions.ts:1729, ab966c214be0)
• Proof state: The live PR body lists targeted test/autoreview/diff-check commands but no redacted terminal output, logs, screenshot, recording, or linked artifact from an after-fix branch/restore run. (fc1315f15e16)
• Related resubmission: The only matching title search results are this open PR and the earlier closed unmerged resubmission source, which was closed for the active-PR limit rather than replaced by a merged fix.

Likely related people:

• scoootscooob: Authored and merged the original compaction checkpoint feature that introduced the gateway checkpoint helpers and sessions.compaction RPC surface. (role: feature owner; confidence: high; commits: f4fcaa09a358; files: src/gateway/session-compaction-checkpoints.ts, src/gateway/server-methods/sessions.ts, src/config/sessions/types.ts)
• RomneyDa: Live PR history shows this account authored and merged the recent broad commit currently blamed for the accessor and gateway checkpoint lookup lines. (role: recent line owner; confidence: medium; commits: 751a6c23f098; files: src/config/sessions/session-accessor.ts, src/gateway/session-compaction-checkpoints.ts, src/gateway/server-methods/sessions.ts)
• steipete: Shortlog and recent git history show heavy work across the same gateway/session/accessor files, including adjacent session and gateway refactors. (role: adjacent area contributor; confidence: medium; commits: e7d33b4870f7, 9e0d35869521, 3174c6919de1; files: src/gateway/session-compaction-checkpoints.ts, src/gateway/server-methods/sessions.ts, src/config/sessions/session-accessor.ts)
• vincentkoc: The live PR is assigned to this account, and git history shows adjacent gateway/session touches in the same file set. (role: assigned reviewer and recent adjacent contributor; confidence: medium; commits: aa69b12d0086, 74e7b8d47b18; files: src/gateway/session-compaction-checkpoints.ts, src/gateway/server-methods/sessions.ts, src/config/sessions/session-accessor.ts)

• 🦀 challenger crab: rare, exceptional readiness with strong proof, clean implementation, and convincing validation.
• 🦞 diamond lobster: very strong readiness with only minor maintainer review expected.
• 🐚 platinum hermit: good normal PR, likely mergeable with ordinary maintainer review.
• 🦐 gold shrimp: useful signal, but proof or patch confidence is still limited.
• 🦪 silver shellfish: thin signal; proof, validation, or implementation needs work.
• 🧂 unranked krab: not merge-ready because proof is missing/unusable or there are serious correctness or safety concerns.
• 🌊 off-meta tidepool: rating does not apply to this item.

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