fix(code): coalesce writeLocalLogs per taskRunId to stop main-thread storm

[k11kirky]

Summary

Layer 1 of a multi-PR fix for the launch hang and "can't click cloud task" symptoms reported by cloud-task users.

Extracts local NDJSON cache handling (readLocalLogs / writeLocalLogs) into a singleton LocalLogsService and single-flights writes per taskRunId with latest-wins coalescing. If a write is already in flight when another arrives for the same run, the new content replaces any queued content rather than spawning a parallel fs.promises.writeFile.

Why this is needed

When the renderer's gap-reconcile loop fires on every SSE snapshot — which happens whenever parseLogContent silently drops corrupted lines and processedLineCount never catches up to the server's expectedCount — the old fire-and-forget writeLocalLogs piles fs.promises.writeFile continuations onto the main process, producing the FileHandle::CloseReq::Resolve saturation signature we saw at app launch.

This is one of two distinct main-thread hangs reported on the same crash signature:

• #2242 (merged) addressed the startup unzipSync path that affected all users.
• This PR addresses the cloud-task corruption-feedback loop that only manifested for users with cloud tasks.

What this does NOT fix

Stops the storm, but doesn't address the underlying corruption-amplification loop or unbounded reconnects — those are layer 2 and 3 below.

Follow-ups (separate PRs to be stacked on this one)

Layer 2 — break the corruption-amplification feedback loop.
parseLogContent (renderer service.ts:3539) silently drops malformed lines, so processedLineCount < expectedCount forever and every SSE snapshot triggers another gap-reconcile + S3 fetch + overwrite. Need to either:

• Track dropped-line counts and feed them into the reconciliation math so a known-corrupted file stops triggering gap-reconcile after one observation, or
• Hash-compare local vs S3 content and short-circuit re-write when they match.

Fixes the "can't click on cloud task" symptom for users whose local NDJSON is already poisoned.

Layer 3 — bound the reconnect budget.
MAX_SSE_RECONNECT_ATTEMPTS = 5 (cloud-task/service.ts:21) is defeated by two paths:

• handleStreamCompletion reconnects with countAttempt: false for non-terminal clean EOF (cloud-task/service.ts:1057).
• retry / retryUnhealthyCloudSessions resets the counter on every focus.

Need a per-run cumulative cap and an explicit unrecoverable terminal state so the UI can surface "this run is broken" instead of looping silently.

Separate ticket — S3 source corruption.
The agent's local writer (packages/agent/src/session-log-writer.ts:391) correctly appends \n, but user logs show records concatenated without separators across days. Missing newlines are being introduced somewhere in the agent-server upload/aggregation path. This PR limits the blast radius of corruption but doesn't stop it from being produced.

Test plan

• Unit tests cover: single-flight coalescing, multi-run independence, propagation of in-flight resolution to all coalesced callers, recovery after write rejection, queue draining after completion.
• pnpm --filter code typecheck clean.
• pnpm --filter code test — new tests pass; remaining failures are pre-existing archive integration tests unrelated to this change.
• Manual verification on a dev build with cloud tasks (post-merge).

[greptile-apps]

Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
apps/code/src/main/services/local-logs/service.test.ts:79-93
**Prefer parameterised tests for equivalent null-return cases**

The two `readLocalLogs` tests — `"returns null when the file is missing"` and `"returns null on other read errors"` — differ only in the error object injected. Per the team style, these should be collapsed into a single `it.each`.

_{Reviews (1): Last reviewed commit: "fix(code): coalesce writeLocalLogs per t..." | Re-trigger Greptile}

[greptile-apps]

Prefer parameterised tests for equivalent null-return cases

The two readLocalLogs tests — "returns null when the file is missing" and "returns null on other read errors" — differ only in the error object injected. Per the team style, these should be collapsed into a single it.each.

Context Used: Do not attempt to comment on incorrect alphabetica... (source)

Prompt To Fix With AI

This is a comment left during a code review.
Path: apps/code/src/main/services/local-logs/service.test.ts
Line: 79-93

Comment:
**Prefer parameterised tests for equivalent null-return cases**

The two `readLocalLogs` tests — `"returns null when the file is missing"` and `"returns null on other read errors"` — differ only in the error object injected. Per the team style, these should be collapsed into a single `it.each`.

**Context Used:** Do not attempt to comment on incorrect alphabetica... ([source](https://app.greptile.com/review/custom-context?memory=instruction-0))

How can I resolve this? If you propose a fix, please make it concise.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!

[k11kirky]

• fix(code): bound cloud session reconnect attempts with cumulative cap #2285
• fix(code): break unrecoverable cloud log reconcile loop on stable deficiency #2284
• fix(code): coalesce writeLocalLogs per taskRunId to stop main-thread storm #2255 👈 (View in Graphite)
• main

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