fix(dashboard): atomic, non-fatal statusline writes

[TraderSamwise]

Problem

The dashboard could crash on startup with:

aimux: failed to spawn "undefined": ENOENT: no such file or directory,
rename '…/tmux-statusline/bottom-dashboard-…-client-….txt.tmp' → '…txt'
aimux dashboard failed to start.

Two defects:

1. Racy statusline write. rewriteLocalStatuslineArtifacts (src/main.ts) hand-rolled an "atomic" write using a single shared <file>.tmp path. When more than one client/refresh writes the same statusline file concurrently, they collide on that temp path and one renames the other's temp out from under it → ENOENT on rename. A cosmetic statusline write then took down the whole dashboard.
2. Misleading error. In dashboard mode tool is undefined, so the top-level catch printed failed to spawn "undefined" for what was really a dashboard-startup error.

Fix

• Statusline writes now use the existing writeTextAtomic (unique per-write temp name + mkdir -p + fsync) instead of a shared .tmp, and are wrapped in try/catch so a write failure is logged and ignored — statusline is cosmetic tmux chrome and must never abort dashboard startup.
• The catch reports dashboard failed to start when there is no tool, instead of failed to spawn "undefined".

Test

atomic-write.test.ts: 50 concurrent writers to one path never ENOENT, leave a valid final value, and litter no temp files.

yarn typecheck / lint / build / full vitest (1115) all pass.

🤖 Generated with Claude Code

Summary by CodeRabbit

• Tests

  • Added test coverage for atomic file write operations to ensure race-condition safety.

• Bug Fixes

  • Improved file write reliability by implementing atomic write operations across statusline and artifact updates, preventing partial writes and data corruption in concurrent scenarios.

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Project	Deployment	Actions	Updated (UTC)
app	Ready	Preview, Comment	Jun 14, 2026 7:44am

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No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: f4e8b54a-4553-49f5-ae9e-207a41c0d20b

📥 Commits

Reviewing files that changed from the base of the PR and between f9b5f7d and 9e73bcc.

📒 Files selected for processing (4)

• src/atomic-write.test.ts
• src/main.ts
• src/multiplexer/dashboard-control.ts
• src/multiplexer/persistence-methods.ts

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📝 Walkthrough

Walkthrough

Three statusline file-writing call sites in main.ts, dashboard-control.ts, and persistence-methods.ts are migrated from manual .tmp + renameSync to the shared writeTextAtomic helper, with write failures caught and logged via debug. A new test in atomic-write.test.ts verifies that writeTextAtomic uses a unique temp path even when a directory exists at the conventional .tmp collision path.

Changes

Atomic write migration for statusline files

Layer / File(s)	Summary
Migrate statusline writers to writeTextAtomic src/multiplexer/persistence-methods.ts, src/multiplexer/dashboard-control.ts, src/main.ts	Removes renameSync/writeFileSync direct imports; adds writeTextAtomic/writeJsonAtomic and debug imports. All three statusline write implementations (writeStatuslineFile, writeStatuslineTextFile, rewriteLocalStatuslineArtifacts) now delegate to writeTextAtomic inside a try/catch that swallows errors and logs via debug. Also updates the CLI top-level error message to differentiate tool-spawn failures from dashboard startup failures.
Race-collision test for unique temp paths src/atomic-write.test.ts	Adds mkdirSync to the test import; adds a new test that pre-creates a directory at ${target}.tmp to simulate a path collision, then asserts the write completes successfully, the target content is correct, and no .tmp files remain.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• TraderSamwise/aimux#99: Introduced the writeTextAtomic helper and its atomic temp-file semantics that this PR adopts across all statusline write sites.

Poem

🐇 No more shared .tmp in the warren's hall,
Each write gets its own burrow, safe from all,
Renaming by hand was a rickety gate—
Now writeTextAtomic keeps files straight.
No collisions, no races, no leftover mess,
Just atomic hops forward, nothing less! 🌿

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly and concisely summarizes the main change: converting statusline writes to atomic operations with non-fatal error handling. It is clear, specific, and captures the primary objectives of the changeset.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

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🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/statusline-atomic-write

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