fix(#4806): unparseable VERIFICATION.md frontmatter reports a distinct parse error, never status missing (#4896)

* test(#4806): failing-first — unparseable VERIFICATION.md frontmatter is a parse error, not status missing / Field not found

* fix(#4806): unparseable VERIFICATION.md frontmatter reports a distinct parse error — never 'missing' or 'Field not found'

* test(#4806): census pin 66→67 — cmdFrontmatterGet's unparseable-frontmatter error is a new output({error}) call site

* chore(#4806): backfill changeset PR number (4896)

---------

Co-authored-by: sim <sim@local>

src/frontmatter.cts

@@ -1378,6 +1378,14 @@ function cmdFrontmatterGet(cwd: string, filePath: string, field: string | undefi
   // Pass the resolved path so a truncated file is named in the diagnostic and deduplicated
   // per file rather than per content digest (#1882, ADR-1411 wiring clause).
   const fm = extractFrontmatter(content, fullPath);
+  // #4806: an unparseable frontmatter block is a distinct outcome — the file
+  // HAS a frontmatter block but its YAML failed to parse. Reporting
+  // "Field not found" tells the caller the key is absent, which is
+  // indistinguishable from a file that genuinely lacks it.
+  if ((fm as unknown as Record<symbol, unknown>)[FRONTMATTER_UNPARSEABLE] === true) {
+    output({ error: 'Frontmatter is not parseable YAML — fix the syntax error in the frontmatter block', path: filePath }, raw, undefined);
+    return;
+  }
   if (field) {
     const value = fm[field];
     if (value === undefined) { output({ error: 'Field not found', field }, raw, undefined); return; }

src/verification.cts

@@ -49,7 +49,7 @@ import { isContainedIn } from './security.cjs';
 
 const { output, error } = io;
 const { extractPhaseToken, scopeToPhase } = phaseId;
-const { extractFrontmatter } = frontmatterMod;
+const { extractFrontmatter, FRONTMATTER_UNPARSEABLE } = frontmatterMod;
 const { normalizeLineEndings } = coreUtilsMod;
 const { SCOPE } = planningScopeMod;
 type Scope = planningScopeMod.Scope;
@@ -128,6 +128,15 @@ const VERIFICATION_ROUTING_TABLE: Record<string, VerificationRoute> = {
     next_action: 'No verification report found — the verify step never completed. Running execute-phase is safe here: it resumes at the verification gates and does not re-run plans that already have a SUMMARY.md (see #2868).',
     next_command: 'execute-phase',
   },
+  // #4806: the report EXISTS but its frontmatter is not parseable YAML —
+  // fundamentally different from "missing" (the verify step DID run; re-running
+  // execute-phase cannot fix a YAML typo). Consumers treat any non-'passed'
+  // status as blocking, so this value fails safe while telling the truth.
+  unparseable: {
+    status: 'unparseable',
+    next_action: "The *-VERIFICATION.md frontmatter is not parseable YAML — fix the syntax error in the report itself. Re-running execute-phase cannot fix a YAML typo in an existing report.",
+    next_command: '',
+  },
   // INTERNAL SENTINEL: constructed when the file has a status value not in
   // VERIFIER_STATUSES. Never emitted by the verifier.
   unknown: {
@@ -1028,6 +1037,16 @@ function readVerificationStatus(
     // same root cause as the false-clean class fixed elsewhere in #3707-CR.
     const content = normalizeLineEndings(fsImpl.readFileSync(filePath, 'utf-8'));
     fm = extractFrontmatter(content, filePath);
+    // #4806: an unparseable frontmatter block is NOT "missing" — the file
+    // exists and verification ran. Report a distinct status so the caller is
+    // sent to fix the YAML, not to re-run execute-phase.
+    if ((fm as unknown as Record<symbol, unknown>)[FRONTMATTER_UNPARSEABLE] === true) {
+      return {
+        status: 'unparseable',
+        next_action: "The *-VERIFICATION.md frontmatter is not parseable YAML — fix the syntax error in the report itself. Re-running execute-phase cannot fix a YAML typo in an existing report.",
+        next_command: '',
+      };
+    }
     const statusVal = fm['status'];
     // status is always a scalar string in a well-formed VERIFICATION.md frontmatter;
     // only accept string values — arrays and objects are not valid status values.