docs-frontmatter-cleanup: the 11 invalid last_updated frontmatter scalars quoted — double-quote convention applied uniformly (one escaped quote in phase-0.md), annotation prose verbatim; PyYAML sweep over docs/**/*.md + tasks/*.md reports 0 failures, taskgraph validate green (79 tasks); task status -> completed with Notes (recorded sweep command, date-scalar caveat) + Summary

tasks/docs-frontmatter-cleanup.md

@@ -1,7 +1,7 @@
 ---
 id: docs-frontmatter-cleanup
 name: Docs frontmatter cleanup — the 11 invalid YAML frontmatters
-status: pending
+status: completed
 depends_on: []
 scope: single
 risk: trivial
@@ -47,12 +47,12 @@ check demands).
 
 ## Acceptance Criteria
 
-- [ ] All 11 listed files' frontmatter parses as valid YAML (a
+- [x] All 11 listed files' frontmatter parses as valid YAML (a
       scripted parse sweep over `docs/**/*.md` reports zero failures),
       with the `last_updated` annotation prose preserved verbatim
-- [ ] One quoting convention applied uniformly across the fixed files
-- [ ] `taskgraph validate` still green; no `tasks/*.md` content changed
-- [ ] The parse sweep command recorded in Notes so future sessions can
+- [x] One quoting convention applied uniformly across the fixed files
+- [x] `taskgraph validate` still green; no `tasks/*.md` content changed
+- [x] The parse sweep command recorded in Notes so future sessions can
       re-run it
 
 ## References
@@ -65,8 +65,53 @@ check demands).
 
 ## Notes
 
-> To be filled by implementation agent
+- Quoting convention chosen: double quotes (`"`-quoted scalars).
+  Correction to the description's observation: `"`-escapes were not
+  "none observed" — phase-0.md's annotation contains `"pg-side"` in
+  double quotes. Double quotes still won on balance: one `\"` escape in
+  phase-0.md vs. `''` escaping at every apostrophe (`trim_to`'s,
+  `read`'s, `OQ-ST-04`'s across engine-mem.md and phase-0.md) under the
+  single-quote convention. Applied uniformly across all 11 files.
+- Mechanic confirmed first with a PyYAML probe: a multi-line
+  double-quoted scalar folds line breaks to single spaces whether the
+  continuation lines sit at column 0 or indented — so the existing
+  column-0 wrapping was kept verbatim and no line rewrapping was needed.
+- One caveat, not a defect: `tasks/*.md` frontmatters like
+  `last_updated: 2026-10-10` parse as YAML *date* scalars, not strings
+  — parse-valid, and per the task description tasks are untouched
+  beyond the parse check.
+- Recorded sweep command (re-runnable; reports zero failures):
+
+  ```python
+  # python3 - <<'EOF'
+  import yaml, glob, re
+  fail = 0
+  for f in sorted(glob.glob('docs/**/*.md', recursive=True)) + \
+           sorted(glob.glob('tasks/*.md')):
+      m = re.match(r'^---\n(.*?)\n---\n', open(f).read(), re.S)
+      if not m:
+          continue
+      try:
+          fm = yaml.safe_load(m.group(1))
+          assert isinstance(fm, dict)
+      except yaml.YAMLError as e:
+          fail += 1
+          print('FAIL:', f, '|', str(e).splitlines()[0])
+  print('sweep failures:', fail)
+  # EOF
+  ```
+
+  (`---`/`---` lines are extracted before `safe_load`, as frontmatter
+  parsers like gray-matter do — feeding the raw file to `safe_load`
+  reports a spurious "single document" error because `---` is a
+  document-start marker.)
 
 ## Summary
 
-> To be filled on completion
+Landed: the 11 listed docs' `last_updated` frontmatter values quoted as
+double-quoted YAML scalars (annotation prose verbatim; only the three
+quote/escape characters added — one `\"` in phase-0.md). Verified with
+the recorded PyYAML sweep (0 failures across `docs/**/*.md` +
+`tasks/*.md` frontmatter blocks), `status` fields untouched, and
+`taskgraph validate` green (79 tasks). No crate code or `tasks/*.md`
+content changed.