Singleton Lock

Coordinate exclusive access to a named singleton resource across parallel agents using a filesystem-backed lock with atomic acquire, adaptive backoff, and stale-holder reaping. Use this skill whenever two or more agents running in parallel will eventually need to touch the same singleton — Chrome DevTools MCP (one browser, one driver), Playwright runner via `mcp__devtools__start_tests` (only one run at a time), a local Java backend (only one worktree can hold the claim), a shared GPU or build agent, an external API with a strict rate limit, or any other "there is exactly one of these and we have N agents who want it" situation. Trigger when the user says things like "run …