diff --git a/.github/workflows/rust-ci.yml b/.github/workflows/rust-ci.yml
index b12c5e5c..e41d95cb 100644
--- a/.github/workflows/rust-ci.yml
+++ b/.github/workflows/rust-ci.yml
@@ -22,6 +22,7 @@ on:
       - PHILOSOPHY.md
       - ROADMAP.md
       - scripts/roadmap-*.sh
+      - tests/test_roadmap_helpers.py
       - docs/**
       - rust/**
   pull_request:
@@ -43,6 +44,7 @@ on:
       - PHILOSOPHY.md
       - ROADMAP.md
       - scripts/roadmap-*.sh
+      - tests/test_roadmap_helpers.py
       - docs/**
       - rust/**
   workflow_dispatch:
@@ -76,6 +78,8 @@ jobs:
         run: python .github/scripts/check_release_readiness.py
       - name: Check ROADMAP ids
         run: scripts/roadmap-check-ids.sh
+      - name: Check ROADMAP helper behavior
+        run: python -m unittest discover -s tests -p test_roadmap_helpers.py
 
   fmt:
     name: cargo fmt
diff --git a/ROADMAP.md b/ROADMAP.md
index f44ea0a8..89ff2be3 100644
--- a/ROADMAP.md
+++ b/ROADMAP.md
@@ -7615,3 +7615,5 @@ Original filing (2026-04-18): the session emitted `SessionStart hook (completed)
 723. **Concurrent dogfood claws allocate ROADMAP ids manually and collide — same id reused by two contributors simultaneously, causing PR ROADMAP.md conflicts and lost entries** — observed live 2026-05-26 during Jobdori+Gaebal parallel dogfood session: Gaebal filed stale-local-probe as #719; Jobdori landed `plugins list <filter>` as #719 on main first; Gaebal shifted to #720; Jobdori landed `claw help <topic>` as #720; stale-local-probe eventually landed as #721 after two forced rebase cycles. The ROADMAP append workflow has no reservation or conflict-aware id allocation. **Required fix shape:** (a) add `scripts/roadmap-next-id.sh` that reads the highest id from ROADMAP.md and prints `highest+1` — claws should call this immediately before appending any new entry; (b) document in CONTRIBUTING.md that id allocation is optimistic-append: call `roadmap-next-id.sh` immediately before the append, git-pull first, resolve collisions at push time by re-numbering the appended entry; (c) long-term: a GitHub Action that validates no duplicate ROADMAP ids on PR would catch this before merge. Added `scripts/roadmap-next-id.sh` (this commit). Source: Gaebal Gajae live observation, 2026-05-26.
 
 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]
diff --git a/scripts/roadmap-next-id.sh b/scripts/roadmap-next-id.sh
index 4505aa69..3db4c49d 100755
--- a/scripts/roadmap-next-id.sh
+++ b/scripts/roadmap-next-id.sh
@@ -10,24 +10,47 @@
 #   ${NEXT}. **...description...**
 #   EOF
 #
-# The script reads the highest numeric id prefix from ROADMAP.md and
-# prints highest+1.  It does not lock the file; callers working in
-# parallel should git-pull immediately before appending, run
-# scripts/roadmap-check-ids.sh before push, and resolve any append
-# collision at git-push time.
+# The script first validates helper-era ids with roadmap-check-ids.sh, then
+# reads the highest numeric id prefix from ROADMAP.md and prints highest+1. It
+# does not lock the file; callers working in parallel should git-pull
+# immediately before appending, run scripts/roadmap-check-ids.sh before push,
+# and resolve any append collision at git-push time.
 set -euo pipefail
 
 ROADMAP="${1:-ROADMAP.md}"
+SCRIPT_DIR="$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd -P)"
+CHECKER="$SCRIPT_DIR/roadmap-check-ids.sh"
 
 if [[ ! -f "$ROADMAP" ]]; then
   echo "error: ROADMAP not found at $ROADMAP" >&2
   exit 1
 fi
 
-# Find the highest leading integer from lines that start with a number + '.'.
-highest=$(grep -E '^[0-9]+\.' "$ROADMAP" | grep -Eo '^[0-9]+' | sort -n | tail -1)
+if [[ ! -f "$CHECKER" || ! -r "$CHECKER" ]]; then
+  echo "error: required ROADMAP id checker not found or not readable at $CHECKER" >&2
+  echo "error: refusing to print a next id without duplicate-id validation" >&2
+  exit 1
+fi
 
-if [[ -z "$highest" ]]; then
+if ! checker_output="$(bash "$CHECKER" "$ROADMAP" 2>&1)"; then
+  printf '%s\n' "$checker_output" >&2
+  exit 1
+fi
+
+# Find the highest leading integer from lines that start with a number + '.'.
+highest=$(awk '
+  /^[0-9]+\./ {
+    id = $0
+    sub(/\..*/, "", id)
+    id += 0
+    if (id > highest) {
+      highest = id
+    }
+  }
+  END { print highest + 0 }
+' "$ROADMAP")
+
+if [[ "$highest" -eq 0 ]]; then
   echo 1
 else
   echo $(( highest + 1 ))
diff --git a/tests/test_roadmap_helpers.py b/tests/test_roadmap_helpers.py
new file mode 100644
index 00000000..0169f88c
--- /dev/null
+++ b/tests/test_roadmap_helpers.py
@@ -0,0 +1,67 @@
+from __future__ import annotations
+
+import shutil
+import subprocess
+import tempfile
+import unittest
+from pathlib import Path
+
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+NEXT_ID = REPO_ROOT / 'scripts' / 'roadmap-next-id.sh'
+
+
+def run_next_id(roadmap: Path, script: Path = NEXT_ID) -> subprocess.CompletedProcess[str]:
+    return subprocess.run(
+        ['bash', str(script), str(roadmap)],
+        cwd=REPO_ROOT,
+        capture_output=True,
+        text=True,
+        check=False,
+    )
+
+
+class RoadmapHelperTests(unittest.TestCase):
+    def test_roadmap_next_id_prints_only_next_id_after_duplicate_check(self) -> None:
+        with tempfile.TemporaryDirectory() as temp_dir:
+            roadmap = Path(temp_dir) / 'ROADMAP.md'
+            roadmap.write_text('721. old\n723. helper era\n724. guard\n')
+
+            result = run_next_id(roadmap)
+
+        self.assertEqual(0, result.returncode)
+        self.assertEqual('725\n', result.stdout)
+        self.assertEqual('', result.stderr)
+
+    def test_roadmap_next_id_fails_fast_on_helper_era_duplicate(self) -> None:
+        with tempfile.TemporaryDirectory() as temp_dir:
+            roadmap = Path(temp_dir) / 'ROADMAP.md'
+            roadmap.write_text('722. legacy\n999. first\n999. duplicate\n')
+
+            result = run_next_id(roadmap)
+
+        self.assertNotEqual(0, result.returncode)
+        self.assertEqual('', result.stdout)
+        self.assertIn('duplicate ROADMAP numeric id(s)', result.stderr)
+        self.assertIn('999', result.stderr)
+        self.assertNotIn('1000', result.stdout)
+
+    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'
+            script_dir.mkdir()
+            copied_next_id = script_dir / 'roadmap-next-id.sh'
+            shutil.copy2(NEXT_ID, copied_next_id)
+            roadmap = Path(temp_dir) / 'ROADMAP.md'
+            roadmap.write_text('724. guard\n')
+
+            result = run_next_id(roadmap, copied_next_id)
+
+        self.assertNotEqual(0, result.returncode)
+        self.assertEqual('', result.stdout)
+        self.assertIn('required ROADMAP id checker not found or not readable', result.stderr)
+        self.assertIn('refusing to print a next id', result.stderr)
+
+
+if __name__ == '__main__':
+    unittest.main()