docs(handoff): brief for the e2e database-locked defect blocking v1.0.0

[adbarc92]

Documentation only — no code changes.

Adds docs/handoffs/2026-07-25-e2e-database-locked.md, a self-contained brief for whoever picks up the e2e failure, and updates docs/STATUS.md to point at it.

Why

main @ 74cadcf has everything from PRs #9/#10/#11. backend (3.11), backend (3.12), frontend, and validate-config are green. e2e is not — it fails with claim_next_task failed: database is locked. That is now the only known functional defect, and the release is deliberately held behind it.

What the brief carries

• The reproduction, and the fact that it may not reproduce locally (CI runners are slower — widen the window rather than dismissing it).
• The leading hypothesis, explicitly marked unverified: backend/main.py:99 passes a constant data/web.db into start_run() on every start_project, and each start_run spawns its own state server plus 4 workers. Two concurrent runs therefore put two OS processes on one SQLite file, which the store's asyncio.Lock cannot serialise — it is in-process only.
• What is already ruled out: a missing busy_timeout pragma. Python's sqlite3.connect() applies a 5s busy timeout that aiosqlite inherits, so that is not the cause — the brief says so explicitly to stop the next agent burning time there.
• The second, independent problem: the Playwright specs predate the engine rewrite (last touched 2026-06-02) and still assert on the retired LangGraph flow. Two layers, not one.
• A trap worth flagging: the local v1.0.0 tag points at ba82ca8, which predates the fresh-clone fix 7bfa00d and therefore cannot start on a clean checkout. It must be moved before it is ever pushed.

Decisions recorded

Both confirmed by the user this session rather than assumed:

• Hold the v1.0.0 tag and GitHub Release until e2e is green.
• The successor works autonomously.

Four genuinely open questions are carried as open questions rather than silently defaulted — chiefly whether the Playwright specs should be rewritten against the engine's flow or the job retired, which is a user-facing call.