ci: cut runner load from drafts, re-pushes, and the mutation canary

[thymikee]

Summary

Reduces load on GitHub runners. In a 5-hour sample (2026-10-14), the advisory mutation canary used about 16% of runner time, mostly on PRs that only edited a workspace package.json. Agents also re-push often, and each push restarts every lane.

• Mutation canary: LANE_TOOLING is split into LANE_SOURCES (lane code and config, including vitest.config.ts and scripts/lib/) and LANE_DEPENDENCIES (root and workspace package.json, the lockfile).
  • A diff touching only dependencies runs the self-test.
  • Mutants run only through gh workflow run mutation-affected.yml --ref <branch> [-f base=<parent>], which passes --with-dependencies.
• Device smoke lanes: they skip drafts, start on ready_for_review, and cancel on converted_to_draft. A gate test enforces this.
• Agent docs: push once per review round. Allow 2,500 lines for one coherent change with self-contained commits.
  • Two duplicate lines were removed to fit the guidance budget. check:fallow already runs in check:affected. The misrouted-path rule repeats "If selection rules change, plant a failure".

10 files.

Validation

At 2a4c15cb1:

• pnpm check:affected --run passes.
• The mutation and gate workflow tests pass (25/25).
• Removing either draft guard fails the new test, and the new selection test fails on main.
• A fresh-context review's findings were applied, except the two doc deletions above.

No device runs: workflow and tooling changes only.

🤖 Generated with Claude Code

[cubic-dev-ai]

All reported issues were addressed across 11 files

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[github-actions]

Size Report

Metric	Base	Current	Diff
Installed (including dependencies)	5.24 MB	5.24 MB	0 B
Package (unpacked)	5.24 MB	5.24 MB	0 B
Package (download)	1.58 MB	1.58 MB	0 B

Startup median (7 runs, lower is better):

Scenario	Base	Current	Diff
CLI --version	27.1 ms	27.8 ms	+0.6 ms
CLI --help	78.6 ms	79.5 ms	+0.9 ms

[thymikee]

This PR is ready at 2a4c15c, and I found nothing that needs a change. No conflicts. The one red check is Compatibility & Provenance, which hit its 15-minute timeout and was cancelled. The other five jobs on the run are green, and the diff does not touch ci.yml. The only possible overlap is the fallow step, because the diff makes LANE_SOURCES and LANE_DEPENDENCIES unexported in scripts/mutation/run.ts. I could not read the step log, so please re-run that job once before merge. I did not exercise a real draft-to-ready transition or the mutation dispatch path, and I did not rerun the 25/25 tests or pnpm check:affected --run; those rest on reading the workflow YAML and the diff. I also did not trace whether the fixture-artifact wait in setup-fixture-app copes with a ready_for_review run on an unchanged head SHA. Not blocking, and you can take or leave these: https://github.com/callstack/agent-device/blob/2a4c15c/scripts/mutation/run.ts#L660 no longer selects the canary when root package.json, pnpm-lock.yaml or packages/*/package.json change, so a stryker or vitest bump runs only the self-test and the end-to-end run needs a dispatch (you could keep those exact dependency edits in the selection, or name the dispatch step in the checklist for dependency-bump PRs); https://github.com/callstack/agent-device/blob/2a4c15c/docs/agents/pull-requests.md#L19 says drafts skip device lanes but test-app-build-cache.yml still runs on every draft push, so "Drafts skip the platform smoke lanes" would be accurate; and the 2,500-line budget at https://github.com/callstack/agent-device/blob/2a4c15c/docs/agents/pull-requests.md#L34 is a policy change that fits better in its own docs PR.