Protect ROADMAP helper missing-path behavior

Add the missing explicit-path regression so operators keep the current fail-fast contract covered, and record the completed ROADMAP follow-up.

Constraint: scope limited to ROADMAP helper regression coverage plus the DONE roadmap entry; tests/__init__.py is included so the requested python -m unittest tests.test_roadmap_helpers invocation resolves locally instead of an external tests package.

Rejected: changing roadmap-next-id.sh behavior | dogfood showed the script already returns the desired nonzero empty-stdout error.

Confidence: high

Scope-risk: narrow

Directive: Keep stdout reserved for the single next id on successful roadmap-next-id.sh runs.

Tested: python -m unittest tests.test_roadmap_helpers -q; scripts/roadmap-check-ids.sh ROADMAP.md; scripts/roadmap-next-id.sh ROADMAP.md; git diff --check -- ROADMAP.md tests/test_roadmap_helpers.py tests/__init__.py

ROADMAP.md

@@ -7617,3 +7617,5 @@ Original filing (2026-04-18): the session emitted `SessionStart hook (completed)
 724. **DONE — ROADMAP duplicate-id validation guard for helper-era append collisions** — follow-up to #723 after dogfood showed `scripts/roadmap-next-id.sh` still printed 724 and exited 0 when a temp ROADMAP copy already contained a second `723. ...` line. This PR closes the gap for new optimistic-append collisions by adding `scripts/roadmap-check-ids.sh`, wiring it into docs CI and the local pre-push hook, documenting the pre-push command in CONTRIBUTING, and mentioning the guard from `roadmap-next-id.sh`. The guard defaults to ids >=723 so current historical roadmap content and old numbered lists do not block docs-only PRs; `--min-id 1` is available for a strict whole-file audit once legacy collisions are cleaned up. **Verification:** `scripts/roadmap-check-ids.sh` passes on current ROADMAP; a temp copy with an appended duplicate `723.` fails nonzero and lists duplicate id 723 with line numbers. Source: Jobdori dogfood follow-up on origin/main `922c2398`, 2026-05-25. [SCOPE: docs/scripts]
 
 725. **DONE — roadmap-next-id helper now fails closed on helper-era duplicate ids before printing a next id** — follow-up to #724 after dogfood on origin/main 25ee5f3d showed `scripts/roadmap-next-id.sh` could print `1000` and exit 0 when a temp ROADMAP copy already contained two `999.` helper-era entries. This PR makes `roadmap-next-id.sh` resolve `roadmap-check-ids.sh` by its own script directory, run the checker with default helper-era min-id semantics before computing `highest+1`, keep stdout reserved for the single next id on success, and fail closed with a useful error if the checker is unavailable. Added focused pytest coverage for clean next-id output, duplicate fail-fast behavior, and missing-checker fail-closed behavior. **Verification:** `scripts/roadmap-next-id.sh ROADMAP.md` prints `725`; `scripts/roadmap-check-ids.sh ROADMAP.md` passes; a temp ROADMAP with duplicate `999.` exits nonzero and lists duplicate id 999 without printing a next id; `bash -n scripts/roadmap-next-id.sh scripts/roadmap-check-ids.sh` passes; `python -m pytest tests/test_roadmap_helpers.py -q` passes. Source: Jobdori dogfood follow-up on origin/main 25ee5f3d. [SCOPE: docs/scripts]
+
+726. **DONE — roadmap-next-id helper missing explicit ROADMAP path behavior is regression-tested** — follow-up to #725 after dogfood on origin/main 49d5b3fc showed the helper already failed correctly for `scripts/roadmap-next-id.sh /tmp/nonexistent-roadmap` but tests only covered clean next-id output, duplicate fail-fast behavior, and missing-checker fail-closed behavior. This PR adds focused unittest coverage proving a missing explicit ROADMAP path exits nonzero, keeps stdout empty, and reports both `ROADMAP not found` and the requested path on stderr. **Verification:** `python -m unittest tests.test_roadmap_helpers -q`; `scripts/roadmap-check-ids.sh ROADMAP.md`; `scripts/roadmap-next-id.sh ROADMAP.md`. Source: Jobdori dogfood follow-up on origin/main 49d5b3fc. [SCOPE: docs/scripts]

tests/test_roadmap_helpers.py

@@ -46,6 +46,17 @@ class RoadmapHelperTests(unittest.TestCase):
         self.assertIn('999', result.stderr)
         self.assertNotIn('1000', result.stdout)
 
+    def test_roadmap_next_id_fails_when_explicit_roadmap_path_is_missing(self) -> None:
+        with tempfile.TemporaryDirectory() as temp_dir:
+            roadmap = Path(temp_dir) / 'missing-ROADMAP.md'
+
+            result = run_next_id(roadmap)
+
+        self.assertNotEqual(0, result.returncode)
+        self.assertEqual('', result.stdout)
+        self.assertIn('ROADMAP not found', result.stderr)
+        self.assertIn(str(roadmap), result.stderr)
+
     def test_roadmap_next_id_fails_closed_when_checker_is_unavailable(self) -> None:
         with tempfile.TemporaryDirectory() as temp_dir:
             script_dir = Path(temp_dir) / 'scripts'