feat(scanners): the write gate now runs in code, not in the templates' prose

`write-scope.mjs` has existed since M-BUG-41, but only one writer ever called
it. Measured 2026-08-12: 9 files under `scanners/` write to disk, 1 imported
the gate; 21 command templates, 17 mention a write, 5 call `write-scope-cli`.
Five templates paraphrasing one policy is the shape that put the lever table in
five copies (#61) — one level up.

The defect was never "8 ungated writers = 8 bugs". Four of them write the
plugin's own bookkeeping and must STAY ungated: a gate that fires on every run
gets switched off, and then it guards nothing. The defect is that nothing
declared WHICH, so the question was answered by reading, and answered
differently each time it was asked.

`tests/lib/write-gate-coverage.test.mjs` makes the answer structural: every
writer either imports the gate or holds an EXEMPT entry naming where the bytes
land. Seen RED against today's tree before the fix (4 ungated writers), and
each of its four assertions was separately seen red against its own defect.

Two premises in the plan text were falsified by measuring them first:

  - `scan-orchestrator` was carried as "plugin-managed, legitimately exempt".
    `--save-baseline` derives its path from the SCAN TARGET, so `--global`
    lands `~/.claude/.config-audit-baseline.json` — user-scope, require-ok. It
    is gated. `lib/baseline.mjs` is the genuinely exempt one.
  - the first sweep scored 9 writers with a regex that could not match
    `writeFileSync(`, so `lib/backup.mjs` — a real writer — read as clean. The
    guard covers sync and async forms, strips comments before matching, and
    asserts non-emptiness so a regex that stops matching cannot make every
    other assertion vacuously green (#63, #64).

Gated: fix-engine, rollback-engine, campaign-export-cli, scan-orchestrator.
All five call sites share ONE reduction, `evaluateWriteTargets` — four copies
of classify/strongestGate/dedup is the drift this exists to prevent.

`campaign export` still DISCLOSES rather than refuses: cross-repo is by design
there, and tightening it into a refusal would break the feature. A dry run is
still not a write, so it is never gated (#63). A refusal is a verdict about a
config that WAS examined, so it rides in the payload and keeps the 0/1/2 exit
contract (#62) — and the verdict now reaches the success payload too, since
stderr is discarded by `2>/dev/null` (F3's class).

commands/fix.md carries `--approve-scope` from the answer the user gives, with
the rule stated where it can be read: classifying is not approving.

Dogfooded end to end: a target outside the session root refuses with zero bytes
written, then applies under `--approve-scope`.

Suite 1703 -> 1707/0. Frozen v5.0.0 + default-output snapshots: 0 changed files.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Pkn22uGCgk6QZA738zNmHL

README.md

@@ -291,6 +291,25 @@ Your team configuration changes over time. Track it:
 
 By default, `/config-audit` auto-detects scope from your git context. Override with: `/config-audit current`, `/config-audit repo`, `/config-audit home`, `/config-audit full`. Use `--delta` for incremental scanning (only new/changed findings).
 
+### Where a write is allowed to land
+
+Reading is machine-wide; **writing is not**. Every write target is classified against the project
+you are standing in, and the classification — not the command doing the asking — decides how
+strong the gate is. A change inside your project applies normally. A write into a *different*
+project is disclosed and then applied, because some commands (like `campaign export`) are
+cross-repo by design. A write to your machine-wide `~/.claude` configuration, or to a path in no
+project at all, is **withheld until you approve that scope explicitly** — it costs, and saves, in
+every project on every turn.
+
+That gate now runs inside the engines, not only in the command prose that wraps them. It covers
+`/config-audit fix`, `/config-audit rollback`, `campaign export`, `--save-baseline`, and
+`optimize --subtract --apply`. When a run is withheld, nothing has been written: you get the
+reason and the affected paths, and you re-run with your approval (`--approve-scope` on the CLIs).
+Approval is always a separate act — classifying a target is not approving it. The plugin's own
+bookkeeping (backups, session state, ledgers, and the report file you named with `--output-file`)
+is deliberately exempt: a gate that fired on every run would be switched off, and then it would
+guard nothing.
+
 ---
 
 ## Deterministic Scanners