parallel-brief

# Parallel brief Concurrency is not the risk; uncoordinated shared state is. Every rule here came from a real failure on 2026-08-03 or 2026-08-04. ## 1. Give every browser run its own server `playwright.config.ts` may reuse an existing local server. Two agents can therefore measure different code while both report success. - Assign a unique port and explicit `PLAYWRIGHT_BASE_URL`. - Use `PLAYWRIGHT_STATIC=1` when proof must cover the exported build. - Run one spec at a time so server failure is distinguishable from product failure. ## 2. One person owns each ratchet baseline Two branches lowering the same literal from one stale starting value cannot be combined arithmetically. The merging owner recounts after integration, lowers the number once, and proves one step lower turns red. Only one agent edits a ratchet file. Others may report measurements, never commit competing baselines. ## 3. Worktrees and stash - Never run `git add -A`; a worktree directory can be staged as an empty gitlink. - Subagents do not remove worktrees. The coordinating owner may remove a task-created worktree only after confirming ownership, preserved changes, and no active users. Otherwise report its path for later cleanup. - Never use `git stash`; stash is repository-wide and has erased another agent's work in this project. ## 4. Keep measurement scratch outside the repository Git may ignore a path that ESLint still scans. Probe files under `output/` or `.tmp/` have inflated warning c...