$ca-preview — reviewer-fleet dry-run

See what codeArbiter would do to your real code before paying any onboarding cost. This is a read-only dry-run against the current uncommitted diff: it predicts which reviewers the change would dispatch, runs the checks that need no project rules, and reports. It never writes state.

It requires no $ca-init, no .codearbiter/ directory, and no decompose or create-context interview. It functions in a repo that never opted in, and it modifies nothing: not the worktree, not the index, not .codearbiter/. git status is unchanged by a run.

Flow

1. Collect the diff. Call the thin entry hook preview.py in diff mode, which wraps collect_diff from hooks/_previewlib.py. It unions HEAD-vs-worktree changes, staged changes, and untracked files (forward-slash paths). Run it from the project root so _previewlib/_hooklib resolve on the same sys.path. Resolve the interpreter once by presence — PY=python3; { command -v python3 >/dev/null 2>&1 && python3 --version >/dev/null 2>&1; } || PY=python — never python3 X || python X, which reruns X on any nonzero exit (#577):

   "$PY" "${PLUGIN_ROOT}/hooks/preview.py" diff
   

   If the result is empty (clean tree, or not a git repo), print a friendly "Nothing to preview" line and STOP. This is a clean exit, not an error: no stack trace, no failure.

2. Predict reviewers by path. Read the reviewer-to-path matrix at includes/review-matrix.md. That include is the single source of truth for which reviewer is dispatched when scope touches a given path: do NOT restate, fork, or inline a second copy of the table here. For each changed path, list the reviewers that WOULD dispatch and name the triggering path for each. This is the same mapping $ca-review uses, so the predicted set matches what a real review would dispatch.

3. Run the state-free secret scan. Call the thin entry hook preview.py in secrets mode, which wraps scan_secrets from hooks/_previewlib.py. It reads each changed file's current content and returns SecretFinding(path, line_no, snippet) for every credential line, with the secret VALUE already masked to **** in snippet:

   "$PY" "${PLUGIN_ROOT}/hooks/preview.py" secrets
   

   Report each finding by path:line_no with its redacted snippet. The snippet arrives already masked: never reconstruct or print a raw secret value.

Report

Emit one clear report with these parts:

• Changed files — the reviewed-file set from step 1, each with its change kind(s) (unstaged, staged, untracked).
• Predicted reviewers — per the matrix, which reviewers would dispatch and the triggering path for each. These are predicted (would-dispatch), not run here.
• Secret findings — the results of the real scan from step 3, by path:line_no with the redacted snippet, marked as found (ran locally), at BLOCK severity. State "none found" when the scan is clean.
• Onboarding nudge — close with one line: the full gated review comes via $ca-init then $ca-review.

Distinct from $ca-doctor

This reports reviewer and gate behavior on the current diff. It makes NO hook-probe claims and says nothing about whether the install's hooks fire: that is $ca-doctor. Do not blend the two.

When NOT to use

• An onboarded repo wanting the full gated verdict → $ca-init then $ca-review.
• Proving the install's hooks actually fire → $ca-doctor.
• A question about the code → $ca-btw.

Hard gate

• Read-only. MUST NOT write, create, or modify any file, including anything under .codearbiter/; MUST NOT stage or commit. git status MUST be unchanged after a run.
• MUST NOT require, trigger, or error on missing $ca-init, .codearbiter/ state, or the decompose / create-context interview.
• MUST NOT print a raw secret value: the lib returns the snippet already redacted, and the report carries only that masked form.
• An empty diff or a non-git directory MUST yield the "Nothing to preview" message and a clean exit, never a stack trace.
• MUST treat the reviewer prediction as predicted (would-dispatch) and the secret scan as found (ran locally): it MUST NOT attribute fabricated findings to any predicted reviewer.