fix(teensy): run flash in build dir + sweep stray dash-flag files (no more -r in repo root)

[zackees]

Problem

bash autoresearch teensy41 (FastLED) intermittently left a 0-byte file literally named -r in the user's project/repo root.

Reproduced: when the deploy port auto-detects to a non-PJRC device (e.g. an ESP32 on the wrong COM port), the teensy deploy takes the teensy_loader_cli -w retry path, and a stray -r appears in the working directory during that window (~110 s in, caught by a filesystem poller). The correct-port native-flash path is clean — hence the intermittency.

Root cause

flash::run_with_retry spawned the loader with cwd=None, so it inherited the fbuild daemon's working directory — typically the user's checkout. A flag-token file (-r) written by a tool/shell mis-parse in that window therefore landed in the repo root.

Exonerated definitively: teensy_loader_cli (its --help exposes no output-file option; running its exact argv --mcu=… -w -v firmware.hex creates nothing), and the fbuild subprocess/containment layer (Windows Job Objects, no file writes). The defect is the inherited cwd, not any one tool.

Fix (crates/fbuild-deploy/src/teensy/flash.rs)

1. Run the flash in the firmware's own build directory (feeding the loader an absolute firmware path so the cwd change can't break the hex read). Any artifact a flash tool leaves now lands in the gitignored build tree, never the user's checkout.
2. sweep_stray_dash_files() — after the flash loop, remove + WARN-log any 0-byte dash-flag file (-r, -w, …) found in the daemon cwd and the flash cwd. Guarantees the repo stays clean, and logs context to attribute the intermittent writer if it recurs.
3. Unit test sweep_removes_empty_dash_flag_files_only (removes empty -r/-w; preserves non-empty -x, normal.txt, and long -verbose).

soldr cargo check -p fbuild-deploy passes.

Reported from FastLED autoresearch teensy41 runs.

🤖 Generated with Claude Code

[coderabbitai]

Warning

Review limit reached

@zackees, you've reached your PR review limit, so we couldn't start this review.

Next review available in: 26 minutes

Enable usage-based reviews in Billing to review now. Otherwise, wait until the next included review is available.
You're only billed for reviews past your plan's rate limits ($0.25/file).

How can I continue?

After more reviews become available, a review can be triggered using the @coderabbitai review command as a PR comment. Alternatively, push new commits to this PR.

To avoid repeated limits, reduce automatic review volume by pausing incremental auto-reviews earlier, using label-based review opt-in, excluding WIP or generated PR titles, or requesting reviews manually when the PR is ready. If your team needs uninterrupted high-volume reviews, an organization admin can enable usage-based reviews.

How do review limits work?

CodeRabbit enforces per-developer PR review limits for each organization. Most developers receive the normal plan review availability.

For paid Pro and Pro+ PR reviews, CodeRabbit uses adaptive limits for sustained high-volume activity. When a developer's recent PR review activity reaches the 95th percentile or higher among CodeRabbit users, additional reviews become available more gradually as earlier reviews age out of the rolling window.

Please refer docs for additional details.

Review details

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: e95ee095-e277-4dfb-b662-1fdac2adf41b

📥 Commits

Reviewing files that changed from the base of the PR and between de36eff and b22aca2.

📒 Files selected for processing (1)

• crates/fbuild-deploy/src/teensy/flash.rs

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/teensy-flash-cwd-stray-r

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}