ci: merge-candidate compares patch-ids without the review documents

The candidate is the branch tip, which already carries the round's
CODE-REVIEW-N-rK.md; the material the reviewer read does not. With
docs/reviews in the diff the two patch-ids never matched once dev had
moved, so every green candidate went back to review whenever another
task published its own document in the meantime — #514 looped twice on
09.09 and #508 only merged when dev happened to stand still. The
patch-id now excludes docs/reviews, exactly like `reviewedFresh` next to
it; a real change of the patch under rebase still returns the task.

Mutant: merge-rereviews-own-review-doc.

Issue: #516
User-Visible: no

scripts/mutation-gate.mjs

@@ -8203,6 +8203,17 @@ const MUTANT_DEFINITIONS = [
       replace: "        if (false) { // mutant: cancelled counts as red",
     }],
   },
+  {
+    id: 'merge-rereviews-own-review-doc',
+    guard: 'node --test test/merge-candidate.test.mjs',
+    because: 'the candidate carries its own review document and the material does not; a patch-id '
+      + 'that counts docs/reviews sends every green candidate back to review whenever dev moved (#516)',
+    patches: [{
+      file: 'scripts/merge-candidate.mjs',
+      find: "      const diff = must(git('diff', '--full-index', from, to, '--', '.', ':!docs/reviews'), 'diff');",
+      replace: "      const diff = must(git('diff', '--full-index', from, to), 'diff'); // mutant: review docs count",
+    }],
+  },
   {
     id: 'merge-trusts-cancelled-dispatch',
     guard: 'node --test test/merge-candidate.test.mjs',