msd-core/docs/how-to/resolve-unreachable-guard-findings.md

How to resolve unreachable-guard findings

npm run lint:ci failed with unreachable-guard-drift. That guard finds shell in shipped prompt files where a fallback arm cannot run — the command it guards succeeds even in the case the fallback was written for, so the guard is output-identical to the success path and silently does nothing.

This page covers reading the finding, fixing each shape, and the one case where acknowledging is the right answer. For why the invariant exists, see ADR-3409.

Read a finding

unreachable-guard-drift: NEW unreachable shell-guard shape(s) found in the prompt layer.
  msd-core/workflows/ship.md:312  cat  cat .planning/phases/*-*/*-SUMMARY.md

Each line is file:line, the token that matched, and the offending source line. For a machine-readable form — useful in CI or when scripting a migration — run the guard with --json:

node scripts/lint-unreachable-guard-drift.cjs --json

That emits one object carrying reason, violations, malformed, stale, baselineErrors, and knownCount. The reason is a frozen enum code, so assert on it rather than on the human text.

Reason codes

Tell "nothing to report" apart from "could not look" — they are different outcomes and only one of them is good news.

reason	Exit	Meaning
ok_no_violations	0	Clean. Every scanned file passed.
ok_baseline_updated	0	You ran --update; the baseline was rewritten.
fail_fresh_violation	1	A new instance of Shape B (Shape A was retired upstream, #3884 — see below). Fix it — see below.
fail_stale_entry	1	A baseline entry matched fewer occurrences than it acknowledges. Either a site was migrated (good — re-record) or only some copies were (finish the job).
fail_malformed_marker	1	A # msd-scan-ignore: whose reason names no issue or URL. Not a violation — a broken exemption.
fail_baseline_load	1	The baseline file is missing, empty, not JSON, or structurally wrong. The guard could not look; this is not a clean run.

Shape A — --pick with an || echo fallback (resolved upstream, #3884)

This shape is no longer a finding. As of #3884 (ADR-3473 §8.4), --pick <field> exits non-zero — not 0 — when the field is absent, so the guard no longer flags a line carrying both --pick and || echo; see the --pick <field> contract for the full three-outcome table. The example below is kept for historical context (this page previously taught the workaround for the defect), and because the shape it shows is now the correct, idiomatic way to write this:

# Previously BROKEN (pre-#3884): the fallback could never fire, because an
# absent field printed '' at exit 0. As of #3884 this now works as written —
# `|| echo "false"` fires exactly when `active` cannot be resolved.
AUTO_MODE=$(msd_run query check auto-mode --pick active 2>/dev/null || echo "false")

You can confirm the new behavior directly:

node msd-core/bin/msd-tools.cjs query phases.list --pick a_field_that_does_not_exist; echo "exit=$?"

That now prints nothing on stdout, a diagnostic on stderr, and exits 1 (pick_field_absent) — not 0.

The two-line workaround this page used to prescribe is no longer required, but remains harmless:

AUTO_MODE=$(msd_run query check auto-mode --pick active 2>/dev/null)
AUTO_MODE="${AUTO_MODE:-false}"

It still works exactly as before — --pick still prints '' at exit 0 when the field is present but null or empty (that is an answer, not a failure; see the contract's negative space), so ${VAR:-default} still resolves those cases the same way it always did. It is simply no longer the only reachable way to supply a default: the single-line || echo idiom at the top of this section now works too.

A count that returns zero is still not the same as a count that could not be resolved — this half of the contract is unchanged by #3884 and remains the reason a :-0 default on an absent field would be a bug:

PRIOR_SUMMARIES=$(msd_run query phases.list --type summaries --pick count 2>/dev/null)
if [ "$PRIOR_SUMMARIES" = "0" ]; then WALKING_SKELETON=true; fi

phases.list --type summaries --pick count always returns a real integer (never absent), so this comparison is safe as written; a query that can return an absent field must still not paper over that with a :-0 default — repoint the query to one that actually answers, the same guidance as before.

Shape B — a glob whose command succeeds on zero matches

Under shopt -s nullglob an unmatched glob expands to zero operands, so the command still succeeds:

cat .planning/phases/*-*/*-SUMMARY.md          # zero operands -> cat reads STDIN and BLOCKS
ls -d .planning/phases/999* || echo "none"     # zero operands -> ls lists the CWD, exits 0, message never prints

The cat form is the worse one: it hangs rather than failing.

Fix — collect into an array and test for existence:

_SUMMARIES=( .planning/phases/*-*/*-SUMMARY.md )
if [ -e "${_SUMMARIES[0]}" ]; then cat "${_SUMMARIES[@]}"; fi

Use -e, not a count — the lint cannot catch this for you

This is the one thing on this page you must get right unaided, because both forms pass the lint (each removes the glob from the command):

if [ ${#_SUMMARIES[@]} -gt 0 ]; then   # correct ONLY if nullglob is set
if [ -e "${_SUMMARIES[0]}" ]; then     # correct either way

Without nullglob, an unmatched glob leaves the literal pattern as a single element, so the count is 1 and the count guard passes wrongly. Measured:

	${#_A[@]} -gt 0	-e "${_A[0]}"
no nullglob, no match	passes (wrong)	skips
nullglob set, no match	skips	skips

nullglob is frequently set in a different fenced block of the same file, so you cannot tell from the line you are editing. Use -e and stop having to know.

msd-core/workflows/review.md keeps count guards because that block sets nullglob two lines above them — correct in context, not a template to copy.

What does not fire

Deliberately, so the guard stays worth reading:

• ls foo/*.md 2>/dev/null | head -1 and X=$(ls -d …) — stdout is consumed, not the exit code. Not a guard.
• ls foo/*.md 2>/dev/null || true — suppressing a failure; there is no fallback value to defeat.
• msd_run query config-get <key> … || echo "default" — config-get genuinely exits 1 on a missing key, so its || works. Verify with node msd-core/bin/msd-tools.cjs query config-get no.such.key; echo $?.
• for f in dir/*.md; do — the construct nullglob exists to make correct.

Acknowledge a finding you cannot fix yet

Only when the fix belongs to another tracked issue. Run:

node scripts/lint-unreachable-guard-drift.cjs --update

This rewrites scripts/baselines/unreachable-guard-drift-baseline.json, keyed on (file, trimmed text) with a per-pair count — never line numbers, so unrelated edits do not disturb it. The baseline is shrink-only: a stale entry fails as loudly as a new one, so it cannot quietly become a parking lot.

The guard ships with a zero-entry baseline. Growing it is a real decision, not a way to make the build green — if you find yourself running --update because the finding is inconvenient, you are turning a gate back into a suggestion. Fix the site instead.

Exempt a deliberate counter-example

Documentation that shows the anti-pattern is byte-identical to a regression, so it must declare itself, on the offending line:

cat .planning/phases/*/*-SUMMARY.md   # msd-scan-ignore: #3409 counter-example for the docs

The reason must name an issue (#123) or an http(s):// URL. A free-text, empty, or whitespace-only reason reports fail_malformed_marker — a distinct error, so you are told which of the two problems you have. #0 and a bare http:// are rejected: an exemption with no real ledger never gets revisited.

There is no file allowlist and there will not be one — an allowlist points at the file most likely to grow the next copy.

Related

• ADR-3409 — the invariant, the measurements behind both detectors (one since retired), and the alternatives rejected
• ADR-3180 — the ratchet and whole-repo-discovery mechanism this guard reuses
• CLI-TOOLS.md's --pick <field> contract — the #3884 fix that resolved Shape A upstream and retired its detector
• Resolve edge-coverage findings · Resolve prohibition findings — sibling "the loop surfaced something, here is what to do with it" pages