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

scanners/fix-engine.mjs

@@ -8,6 +8,7 @@ import { readFile, writeFile, rename, stat } from 'node:fs/promises';
 import { dirname } from 'node:path';
 import { parseJson, parseFrontmatter } from './lib/yaml-parser.mjs';
 import { createBackup } from './lib/backup.mjs';
+import { evaluateWriteTargets } from './lib/write-scope.mjs';
 import { runAllScanners } from './scan-orchestrator.mjs';
 import { VALID_EFFORT_LEVELS as SETTINGS_EFFORT_LEVELS } from './settings-validator.mjs';
 
@@ -237,6 +238,42 @@ export async function applyFixes(fixPlans, opts = {}) {
     throw new Error('backupDir is required when not in dryRun mode');
   }
 
+  // Q1 — the scope gate, in code rather than in the command template's prose.
+  //
+  // A file-rename writes TWO paths: the source disappears and `newPath`
+  // appears. Classifying only `plan.file` would let a rename move a repo file
+  // to a machine-wide destination under a `silent` gate.
+  //
+  // `!dryRun` is load-bearing and is the same rule the subtraction axis
+  // settled (#63): the gate guards a WRITE, and a dry run is not one.
+  // `requiresApproval` is reported either way, so a caller planning a run still
+  // learns that approval will be owed before anything is applied.
+  const scope = evaluateWriteTargets(
+    fixPlans.flatMap((p) => (p.newPath ? [p.file, p.newPath] : [p.file])),
+    opts.repoRoot ?? null,
+    opts.home ? { home: opts.home } : {},
+  );
+
+  if (scope.requiresApproval && !opts.approveScope && !opts.dryRun) {
+    // A refused write is a VERDICT about a config that was examined, not a
+    // tool failure (#62) — the caller renders the disclosure and asks. Nothing
+    // is applied, and this is not an exit-3 situation.
+    return {
+      applied: [],
+      failed: [],
+      gate: scope.gate,
+      requiresApproval: true,
+      disclosures: scope.disclosures,
+      refused: fixPlans.map((plan) => ({
+        findingId: plan.findingId,
+        file: plan.file,
+        status: 'refused',
+        reason: 'scope-gate',
+        type: plan.type,
+      })),
+    };
+  }
+
   for (const plan of fixPlans) {
     if (opts.dryRun) {
       applied.push({
@@ -269,7 +306,14 @@ export async function applyFixes(fixPlans, opts = {}) {
     }
   }
 
-  return { applied, failed };
+  return {
+    applied,
+    failed,
+    gate: scope.gate,
+    requiresApproval: scope.requiresApproval,
+    disclosures: scope.disclosures,
+    refused: [],
+  };
 }
 
 /**