fix(ci): the Windows gate failed on its own cleanup after its verdict agreed

The gate did its job — "Windows agrees: all 11 mutations caught, each by the
catcher its definition names" — and then failed the step after it, on

    git checkout -- docs/evidence/p022-stage2-1.result.json

because at that commit the recorded result was not tracked yet, and `git
checkout --` on an untracked pathspec is an error rather than a no-op. A job
whose measurement had already succeeded reported red for a housekeeping line.

Restore-or-remove now, so the step is correct whether or not the file is
tracked at the commit under test, and the cleanup is turned into the assertion
it was always meant to be: the step fails if this gate left a recorded result
behind. That is the invariant worth having — one campaign, one recorded
provenance — and it was previously implied by a command rather than checked.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CYLNQy6tLXqsV1CbuNqsSb

Author: claude

.github/workflows/ci.yml

@@ -393,9 +393,25 @@ jobs:
       # Left uncommitted on purpose: one campaign has one recorded provenance,
       # and it is the Linux run. A second file claiming the same campaign name
       # would make "which tree was measured" ambiguous.
+      #
+      # Restore-or-remove, because the recorded result is tracked at some
+      # commits and not at others, and `git checkout --` on an untracked path
+      # is an error rather than a no-op — which is exactly how the first
+      # version of this step failed a job whose verdict had already agreed.
+      # The assertion is the point, not the cleanup: the step fails if this
+      # gate left a result behind.
       - name: Confirm nothing was recorded from this run
         if: always()
-        run: git checkout -- docs/evidence/p022-stage2-1.result.json
+        run: |
+          f=docs/evidence/p022-stage2-1.result.json
+          if git ls-files --error-unmatch "$f" >/dev/null 2>&1; then
+            git checkout -- "$f"
+          else
+            rm -f "$f"
+          fi
+          test -z "$(git status --porcelain -- "$f")" \
+            || { echo "FAIL: the Windows gate left a recorded result behind"; exit 1; }
+          echo "OK: the Windows verdict recorded nothing"
 
   # P-022 step 7a (#260) — COMPARE MODE over the committed corpus: the FAST half
   # of #260's test matrix, and one leg of it. The five pinned OSS repositories,