diff --git a/README.md b/README.md
index 907fb28..4e0b47e 100644
--- a/README.md
+++ b/README.md
@@ -1208,13 +1208,14 @@ docker compose run --rm --user root --entrypoint chown test -R "$(id -u):$(id -g
 ```
 
 Every pull request runs `docker build .` against both the latest and the lowest
-supported Go, and must pass before it can be merged — unless it changes none of
-the files the build and its tests read, nor the workflow itself, in which case
-it's skipped. That build runs vet, complexity, the format check, the Go tests and the
-release tooling's tests; the rest of the gate is the changelog check, which CI runs
-against the PR base, and the package-repository checks below. Run `docker build .`
-locally before pushing. The lowest Go builds the `portable` stage, which skips the format
-check and the release tooling's tests:
+supported Go, and must pass before it can be merged — unless it changes none of the
+files the build and its tests read, nor the workflow itself, in which case it's skipped.
+That build runs vet, complexity, the format check, the Go tests, the release tooling's
+tests and the vulnerability filer's tests, which file an item into `todo.md` itself, so
+a change to the plan's shape can fail it; the rest of the gate is the changelog check,
+which CI runs against the PR base, and the package-repository checks below. Run `docker
+build .` locally before pushing. The lowest Go builds the `portable` stage, which skips
+the format check and both Python test suites:
 
 ```sh
 docker build .                                                  # latest
diff --git a/docs/decisions.md b/docs/decisions.md
index ae8a058..5d94965 100644
--- a/docs/decisions.md
+++ b/docs/decisions.md
@@ -1007,4 +1007,6 @@ plan; a test files one into the repository's own `todo.md`. When the next releas
 `todo.md` names no version for it, so the item lands in the release after; the maintainer
 moves it. Where no Go version fixes a vulnerability yet, govulncheck has no ignore list: the
 maintainer drops the job from the release's `needs` until one does, and records why here.
-Valid while the binaries are built from the gate's Go version.
+The paired ruling against f90b4d6 found the project reads worse for it: the gate now reads
+`todo.md`, and a release waits on vuln.go.dev. The maintainer merged it anyway, as the cost
+of filing into the plan. Valid while the binaries are built from the gate's Go version.
diff --git a/vulnerability-filing/file_vulnerabilities.py b/vulnerability-filing/file_vulnerabilities.py
index 37a2c22..dc479d9 100644
--- a/vulnerability-filing/file_vulnerabilities.py
+++ b/vulnerability-filing/file_vulnerabilities.py
@@ -2,7 +2,8 @@
 """File each module's known vulnerabilities as one security item atop todo.md's next release.
 
 Usage: file_vulnerabilities.py <govulncheck -format json report> <todo.md>
-Exits 1 while any vulnerability is known, filed now or before, and 0 on a clean report.
+Exits 1 while any vulnerability is known, filed now or before, 0 on a clean report, and 2 on
+a todo.md it cannot read.
 
 todo.md's `Next ID = N` gives the item's ID, and the release of the plan's top row, the next
 release, gives its release. Its Score is 0.0 until rank_todo.py, which CI cannot run, scores
@@ -21,8 +22,9 @@ import re
 import sys
 from dataclasses import dataclass, field
 
-ROW = re.compile(r"^\| (\d+) \| ([^|]+?) \| [^|]*\| \*\*", re.M)
+ROW = re.compile(r"^\| (?P<id>\d+) \| (?P<release>[^|]+?) \| [^|]*\| \*\*", re.M)
 NEXT_ID = re.compile(r"`Next ID = (\d+)`")
+DETAILS = "## Details\n\n"
 SCORES = {"R": 1, "S": 1, "C": 1, "A": 8, "G": 8}
 GOAL = "1.1"
 
@@ -100,20 +102,30 @@ def detail(module: Module) -> str:
 
 def file_items(modules: list[Module], todo: str) -> tuple[str, list[int]]:
 	"""Return todo.md with an item for each module whose vulnerabilities it does not yet name, and the items' IDs."""
+	first = ROW.search(todo)
+	if first is None:
+		raise ValueError("todo.md has no item to take the next release from")
+	if NEXT_ID.search(todo) is None:
+		raise ValueError("todo.md has no `Next ID = N` line to number the item by")
+	if DETAILS not in todo:
+		raise ValueError(f"todo.md has no {DETAILS.strip()!r} heading to put the item's detail under")
+	release, rows_at = first.group("release"), first.start()
+	details_at = todo.index(DETAILS) + len(DETAILS)
 	filed = []
 	for module in modules:
 		if all(osv in todo for osv in module.osvs):
 			continue
-		first = ROW.search(todo)
-		if first is None:
-			raise ValueError("todo.md has no item to take the next release from")
 		next_id = int(NEXT_ID.search(todo).group(1))
 		line = tagline(module)
 		scores = " | ".join(str(SCORES[k]) for k in "RSCAG")
-		row = f"| {next_id} | {first.group(2)} | security | **{line}** | {scores} | {GOAL} | 0.0 |\n"
-		todo = todo[: first.start()] + row + todo[first.start() :]
-		todo = todo.replace(f"`Next ID = {next_id}`", f"`Next ID = {next_id + 1}`", 1)
-		todo = todo.replace("## Details\n\n", f"## Details\n\n### {next_id}. {line}\n\n{detail(module)}\n", 1)
+		row = f"| {next_id} | {release} | security | **{line}** | {scores} | {GOAL} | 0.0 |\n"
+		text = f"### {next_id}. {line}\n\n{detail(module)}\n"
+		todo = todo[:rows_at] + row + todo[rows_at:]
+		rows_at += len(row)
+		details_at += len(row)
+		todo = todo[:details_at] + text + todo[details_at:]
+		details_at += len(text)
+		todo = NEXT_ID.sub(f"`Next ID = {next_id + 1}`", todo, count=1)
 		filed.append(next_id)
 	return todo, filed
 
@@ -128,7 +140,11 @@ def main(argv: list[str]) -> int:
 	count = sum(len(m.osvs) for m in modules)
 	known = f"{count} known {'vulnerability' if count == 1 else 'vulnerabilities'}"
 	with open(todo_path, encoding="utf-8") as f:
-		todo, filed = file_items(modules, f.read())
+		try:
+			todo, filed = file_items(modules, f.read())
+		except ValueError as err:
+			print(err, file=sys.stderr)
+			return 2
 	if not filed:
 		print(f"{known}, already planned in todo.md.")
 		return 1