thirdshift architect --plan-only: the Architecture review publishes a plan and thirdshift marks it ready #230

Parent

#27

What to build

thirdshift architect --plan-only works end to end. From the Launch directory, with no Issue URL, it:

• does the Run preflight checks that don't need an issue (no Origin match), and the opt-in launch pull;
• creates a worktree detached at the origin head of the Base branch, with no Issue branch;
• runs the Architecture review session with a new Session prompt that names the Factory skills, the Base branch and the optional focus, and asks for the fixed-format final line;
• reads that line, checks the plan issue was created after the Architect run started, is open, and has no unready triage label other than needs-triage;
• swaps needs-triage for ready-for-agent, prints the plan's URL on stdout and exits 0;
• removes the worktree, whatever the outcome.

A failed or interrupted session, or a missing or malformed final line, or a plan that fails its checks, ends the Architect run as a failure with a cause and the session log, and leaves the plan's labels as they are. architect takes an optional free-text focus, which goes into the Session prompt.

Acceptance criteria

• thirdshift architect [focus] --plan-only publishes and marks ready a plan (Spec or single Ticket), prints its URL and exits 0, end to end with the fake claude and gh.
• The parser accepts architect only as the first argument, with an optional focus and --plan-only, and rejects stray arguments; unit tests cover it.
• The Launch directory's checkout is never touched; the worktree is detached at origin/<base> and removed afterwards.
• The Architecture review's Session prompt is in the prompt module and on the prompts page (regenerated with UPDATE_PROMPTS=1 cargo test prompts_page).
• A session that fails, is interrupted, or ends without a valid final line fails the Architect run, shows the session log, and leaves needs-triage on any plan it published.
• A plan issue that's closed, older than the Architect run, or carries another unready label is refused.
• Progress lines cover the review starting, the plan it reported and the label swap.
• thirdshift help and the README document architect, its focus and --plan-only, and say to run one Architect run per repository at a time.

Blocked by

None (can start immediately)