Best possible solution:

Make the exec tail use a UTF-16-safe suffix slice too, keep the new entry/summary boundary coverage, add an exec aggregated boundary test, and require redacted runtime proof before merge.

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

Yes, source-reproducible: the unchanged exec path raw-slices the retained tail before normalization, and a read-only probe showed the retained string can start with low surrogate 0xde00. I did not run a live cron job in this read-only review.

Is this the best way to solve the issue?

No. truncateUtf16Safe is the right helper for entry and summary prefix caps, but the best fix also uses a UTF-16-safe suffix slice for tailText and proves the exec aggregated boundary.

Full review comments:

• [P2] Clamp the exec tail before normalizing diagnostics — src/cron/run-diagnostics.ts:105
  This is the same blocker from the prior ClawSweeper cycle. The new clamps only protect prefix truncation after diagnostics are normalized, but failed exec details still call tailText(aggregated, EXEC_DIAGNOSTIC_TAIL_CHARS), where tailText uses raw value.slice(value.length - maxChars). If an emoji crosses that 2,000-code-unit tail boundary, the retained string starts with a lone low surrogate and the summary path returns it unchanged; make the tail slice UTF-16-safe and add an exec aggregated boundary test.
  Confidence: 0.9

Overall correctness: patch is incorrect
Overall confidence: 0.9

AGENTS.md: found and applied where relevant.

Codex review notes: model internal, reasoning high; reviewed against c9b3358d43f7.

Label justifications:

• P3: This is a narrow cron diagnostic Unicode correctness fix with low blast radius and no config, auth, storage, migration, provider, or delivery behavior change.
• rating: 🧂 unranked krab: Overall readiness is 🧂 unranked krab; proof is 🧂 unranked krab and patch quality is 🦪 silver shellfish.
• status: 📣 needs proof: The PR needs real behavior proof before ClawSweeper can clear the contributor ask. Needs real behavior proof before merge: Missing: the PR body lists focused tests/lint/autoreview only, with no live cron run, terminal transcript, copied output, redacted log, or linked artifact showing after-fix diagnostic truncation; updating the PR body with proof should trigger re-review, or a maintainer can comment @clawsweeper re-review. 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 +1, Tests +23. Total +24 across 2 files.

Acceptance criteria:

• [P1] pnpm test src/cron/run-diagnostics.test.ts after adding exec-tail coverage.
• [P1] Attach redacted terminal output, copied live output, or logs from a cron diagnostic path showing valid Unicode after the fix.

What I checked:

• PR diff changes only prefix clamps: The PR replaces the entry-message and summary prefix .slice(0, limit) calls with truncateUtf16Safe and adds a test for those two boundaries, but it does not change the exec-tail helper. (src/cron/run-diagnostics.ts:105, 90358d973703)
• Current exec tail remains raw-sliced: tailText still keeps the final diagnostic text with value.slice(value.length - maxChars), so the retained text can start inside a surrogate pair. (src/cron/run-diagnostics.ts:89, c9b3358d43f7)
• Exec details use the tail before normalization: Failed exec details feed tailText(aggregated, EXEC_DIAGNOSTIC_TAIL_CHARS) into cron diagnostics before summary and entry normalization run. (src/cron/run-diagnostics.ts:298, c9b3358d43f7)
• UTF-16 helper contract checked: truncateUtf16Safe delegates to sliceUtf16Safe(input, 0, limit), which protects the end boundary of a prefix slice but does not repair a string that already begins with a dangling low surrogate. (packages/normalization-core/src/utf16-slice.ts:44, c9b3358d43f7)
• Read-only source probe reproduced the remaining boundary: A Node probe matching the current helper logic showed a 2,002-code-unit string with an emoji crossing the 2,000-code-unit tail boundary produces a raw tail starting with low surrogate 0xde00, and prefix truncation preserves that leading low surrogate.
• Previous ClawSweeper finding remains unresolved: The existing review comment already identified the exec-tail blocker; the current head added entry/summary tests but left the production tail path unchanged and still has no runtime proof attachment. (90358d973703)

Likely related people:

• steipete: Path history shows recent cron diagnostics commits by this person, and the current PR also contains their added regression-test commit. (role: recent cron diagnostics contributor and adjacent reviewer; confidence: high; commits: c8a953af9371, 875c9fd96dd8, 90358d973703; files: src/cron/run-diagnostics.ts, src/cron/run-diagnostics.test.ts)
• kevinslin: GitHub path history ties the original cron run diagnostics/status surface to commit 89db1e5440f5537790bcc8f5a5fbdddad0eaac46. (role: feature introducer; confidence: high; commits: 89db1e5440f5; files: src/cron/run-diagnostics.ts, src/cron/run-diagnostics.test.ts)
• LiLan0125: Recent cron diagnostics work in the same module added the web_search provider warning path and tests. (role: recent adjacent contributor; confidence: medium; commits: 685b95b607bb; files: src/cron/run-diagnostics.ts, src/cron/run-diagnostics.test.ts)
• lsr911: Related merged UTF-16-safe truncation PRs used the same helper pattern on nearby diagnostic/logging surfaces, which is useful context for consistency. (role: adjacent UTF-16 truncation contributor; confidence: medium; commits: 472e5167d38a, 32de66616303; files: src/agents/tool-policy-audit.ts, extensions/codex/src/app-server/event-projector.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.

Shiny media proof means a screenshot, video, or linked artifact directly shows the changed behavior. Runtime, network, CSP, and security claims still need visible diagnostics.

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• reviewed 2026-07-09T09:49:58.070Z sha bcb72bc :: needs real behavior proof before merge. :: [P2] Clamp the exec tail before normalizing diagnostics
• reviewed 2026-07-09T10:24:33.779Z sha bcb72bc :: needs real behavior proof before merge. :: [P2] Clamp the exec tail before normalizing diagnostics