diff --git a/.github/workflows/guards-nightly.yml b/.github/workflows/guards-nightly.yml
index 17da37b29d..8a0ea9d37b 100644
--- a/.github/workflows/guards-nightly.yml
+++ b/.github/workflows/guards-nightly.yml
@@ -98,24 +98,22 @@ jobs:
       # names a step; each must appear VERBATIM as a `- name:` in this file.
       # Fail-closed: an empty manifest, a missing file or an unreadable line is
       # a failure, never a pass.
+      # EXTRACTED to scripts/check_guards_nightly_manifest.sh (PMAT-3234). The
+      # inline version matched `grep -Fq -- "- name: $name"` — the BARE spelling —
+      # while a step name containing a colon-space must be QUOTED in YAML, and one
+      # of them is. So the matcher looked for `- name: Test-tier...` and the file
+      # said `- name: "Test-tier...`, and this lane went RED naming a step that
+      # runs on every nightly as one the workflow does not run.
+      #
+      # Logic that lives in a `run:` block cannot be unit-tested and cannot carry a
+      # case table; that is why the defect survived. The script matches on the
+      # PARSED name, so all three YAML quotings of one string are one step, and it
+      # ships 7 rows in both directions (a genuinely absent step still fails, and a
+      # manifest that parsed almost nothing is refused rather than passed).
+      - name: Manifest-vs-workflow case table (PMAT-3234, both directions)
+        run: bash scripts/check_guards_nightly_manifest.sh --self-test
       - name: Every step the manifest says moved here must exist here
-        run: |
-          set -euo pipefail
-          manifest=scripts/guards_nightly_manifest.txt
-          [ -s "$manifest" ] || { echo "FAIL: $manifest missing or empty"; exit 1; }
-          n=0; bad=0
-          while IFS=$'\t' read -r secs name; do
-            case "${secs:-}" in ''|'#'*) continue ;; esac
-            [ -n "${name:-}" ] || { echo "FAIL: manifest line has no step name: $secs"; bad=1; continue; }
-            n=$((n + 1))
-            if ! grep -Fq -- "- name: $name" .github/workflows/guards-nightly.yml; then
-              echo "FAIL: manifest names a step this workflow does not run: $name"
-              bad=1
-            fi
-          done < <(grep -vE '^[[:space:]]*(#|$)' "$manifest")
-          [ "$n" -ge 5 ] || { echo "FAIL (vacuity): only $n manifest entries parsed"; exit 1; }
-          [ "$bad" -eq 0 ] || exit 1
-          echo "ok  $n manifest entries, every one a step in this workflow"
+        run: bash scripts/check_guards_nightly_manifest.sh
       # THE COMPARAND, FETCHED ONCE, BEFORE ANY GUARD THAT NEEDS IT -- the
       # SATD step below measures its ceiling on origin/main with the HEAD-built
       # suite, and a depth-1 checkout has no such ref until this runs.
diff --git a/docs/roadmaps/roadmap.yaml b/docs/roadmaps/roadmap.yaml
index 343c44c90b..6d5cf2cfee 100644
--- a/docs/roadmaps/roadmap.yaml
+++ b/docs/roadmaps/roadmap.yaml
@@ -17783,3 +17783,22 @@ roadmap:
   labels:
   - kind:code
   notes: null
+- id: PMAT-3234
+  github_issue: null
+  item_type: task
+  title: 'guards-nightly has been RED on a matcher that cannot see a YAML-quoted step name'
+  status: inprogress
+  priority: high
+  assigned_to: null
+  created: 2026-09-14T19:45:00Z
+  updated: 2026-09-14T19:45:00Z
+  spec: docs/specifications/APR-RELEASE-001-train-and-build-kaizen.md
+  acceptance_criteria: []
+  phases: []
+  subtasks: []
+  estimated_effort: null
+  labels:
+  - kind:code
+  notes: 'a step name containing a colon-space must be quoted in YAML; the inline
+    grep -F matched only the bare spelling, so the lane named a step that runs every
+    night as one the workflow does not run'
diff --git a/scripts/check_guards_nightly_manifest.sh b/scripts/check_guards_nightly_manifest.sh
new file mode 100755
index 0000000000..111676c245
--- /dev/null
+++ b/scripts/check_guards_nightly_manifest.sh
@@ -0,0 +1,110 @@
+#!/usr/bin/env bash
+# check_guards_nightly_manifest.sh — every step scripts/guards_nightly_manifest.txt
+# says moved to guards-nightly.yml must actually be a step in it.
+#
+# THE DEFECT THIS FIXES. The check lived inline in the workflow and matched:
+#
+#     grep -Fq -- "- name: $name" .github/workflows/guards-nightly.yml
+#
+# A fixed-string match against the BARE spelling. But a step name containing a
+# colon-space must be QUOTED in YAML, and one of them does:
+#
+#     manifest:  Test-tier decision case table (BSE-17): quick/full/reuse, drift is ENV
+#     workflow:  - name: "Test-tier decision case table (BSE-17): quick/full/reuse, drift is ENV"
+#
+# so the matcher looked for `- name: Test-tier...` and the file said
+# `- name: "Test-tier...`. guards-nightly has been RED on this since the name was
+# quoted — reporting a step that runs on every nightly as one the workflow does
+# not run. A guard that names a real step as missing is worse than no guard: it
+# trains the reader to ignore it.
+#
+# THE MATCH IS NOW ON THE PARSED NAME, not on a spelling. All three YAML forms of
+# the same string are the same step, so all three match, and a name that is
+# genuinely absent still fails. The case table below pins both directions.
+#
+#   bash scripts/check_guards_nightly_manifest.sh
+#   bash scripts/check_guards_nightly_manifest.sh --self-test
+set -euo pipefail
+
+REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+WORKFLOW="${GUARDS_NIGHTLY_WORKFLOW:-$REPO_ROOT/.github/workflows/guards-nightly.yml}"
+MANIFEST="${GUARDS_NIGHTLY_MANIFEST:-$REPO_ROOT/scripts/guards_nightly_manifest.txt}"
+
+# Every `- name:` in a workflow, with YAML quoting removed. One per line.
+step_names() { # step_names WORKFLOW
+    sed -nE 's/^[[:space:]]*-[[:space:]]+name:[[:space:]]*(.*)$/\1/p' "$1" \
+        | sed -E 's/[[:space:]]+$//' \
+        | sed -E 's/^"(.*)"$/\1/; s/^'"'"'(.*)'"'"'$/\1/'
+}
+
+check() {
+    local n=0 bad=0 secs name names
+    [ -s "$MANIFEST" ] || { printf 'FAIL: %s missing or empty\n' "$MANIFEST" >&2; return 1; }
+    [ -s "$WORKFLOW" ] || { printf 'FAIL: %s missing or empty\n' "$WORKFLOW" >&2; return 1; }
+    names="$(step_names "$WORKFLOW")"
+    while IFS=$'\t' read -r secs name; do
+        case "${secs:-}" in ''|'#'*) continue ;; esac
+        [ -n "${name:-}" ] || { printf 'FAIL: manifest line has no step name: %s\n' "$secs"; bad=1; continue; }
+        n=$((n + 1))
+        if ! grep -Fqx -- "$name" <<<"$names"; then
+            printf 'FAIL: manifest names a step this workflow does not run: %s\n' "$name"
+            bad=1
+        fi
+    done < <(grep -vE '^[[:space:]]*(#|$)' "$MANIFEST")
+    # Vacuity: a manifest that parsed almost nothing would pass by reading nothing.
+    [ "$n" -ge 5 ] || { printf 'FAIL (vacuity): only %s manifest entries parsed\n' "$n" >&2; return 1; }
+    [ "$bad" -eq 0 ] || return 1
+    printf 'ok  %s manifest entries, every one a step in this workflow\n' "$n"
+}
+
+self_test() {
+    local t pass=0 fail=0 rc
+    t="$(mktemp -d)"
+    case "$t" in /tmp/*|/var/tmp/*) : ;; *) printf 'NO-GO: odd mktemp path %s\n' "$t" >&2; return 2 ;; esac
+    row() { if [ "$2" = "$3" ]; then pass=$((pass+1)); printf '  ok    %-48s %s\n' "$1" "$3"
+            else fail=$((fail+1)); printf '  FAIL  %-48s want=%s got=%s\n' "$1" "$3" "$2"; fi; }
+
+    cat > "$t/wf.yml" <<'YML'
+jobs:
+  x:
+    steps:
+      - name: Plain step
+      - name: "Quoted step (BSE-17): has a colon"
+      - name: 'Single quoted step'
+      - name: Trailing space step   
+YML
+    # THE PARSER, four rows: the defect was here and nowhere else.
+    # step_names is in scope here; invoking it through `bash -c 'source ...'`
+    # re-ran this file's own dispatch and returned nothing, which is a broken
+    # HARNESS reporting a working parser as broken — the row that matters most
+    # is the one most easily faked, in either direction.
+    local got
+    got="$(step_names "$t/wf.yml")"
+    grep -Fqx 'Plain step' <<<"$got" && row "bare name parsed" ok ok || row "bare name parsed" no ok
+    grep -Fqx 'Quoted step (BSE-17): has a colon' <<<"$got" && row "DOUBLE-quoted name unquoted (the defect)" ok ok || row "DOUBLE-quoted name unquoted (the defect)" no ok
+    grep -Fqx 'Single quoted step' <<<"$got" && row "single-quoted name unquoted" ok ok || row "single-quoted name unquoted" no ok
+    grep -Fqx 'Trailing space step' <<<"$got" && row "trailing whitespace stripped" ok ok || row "trailing whitespace stripped" no ok
+
+    # END TO END, both directions.
+    printf '1\tPlain step\n2\tQuoted step (BSE-17): has a colon\n3\tSingle quoted step\n4\tTrailing space step\n5\tPlain step\n' > "$t/ok.txt"
+    set +e; GUARDS_NIGHTLY_WORKFLOW="$t/wf.yml" GUARDS_NIGHTLY_MANIFEST="$t/ok.txt" bash "${BASH_SOURCE[0]}" >/dev/null 2>&1; rc=$?; set -e
+    row "manifest fully covered -> pass" "$rc" "0"
+
+    printf '1\tPlain step\n2\tQuoted step (BSE-17): has a colon\n3\tSingle quoted step\n4\tTrailing space step\n5\tA step that is not there\n' > "$t/bad.txt"
+    set +e; GUARDS_NIGHTLY_WORKFLOW="$t/wf.yml" GUARDS_NIGHTLY_MANIFEST="$t/bad.txt" bash "${BASH_SOURCE[0]}" >/dev/null 2>&1; rc=$?; set -e
+    row "a genuinely absent step -> STILL FAILS" "$rc" "1"
+
+    printf '1\tPlain step\n' > "$t/thin.txt"
+    set +e; GUARDS_NIGHTLY_WORKFLOW="$t/wf.yml" GUARDS_NIGHTLY_MANIFEST="$t/thin.txt" bash "${BASH_SOURCE[0]}" >/dev/null 2>&1; rc=$?; set -e
+    row "vacuity floor: <5 entries -> refuse" "$rc" "1"
+
+    printf 'self-test: %s passed, %s failed\n' "$pass" "$fail"
+    [ -n "$t" ] && [ -d "$t" ] && rm -rf "$t"
+    [ "$fail" -eq 0 ]
+}
+
+case "${1:-}" in
+    --self-test) self_test ;;
+    "") check ;;
+    *) printf 'usage: %s [--self-test]\n' "$(basename "$0")" >&2; exit 2 ;;
+esac