tools (volt): checkin_check.py -- a heading inside a fenced block is quoted, not structure

headings_missing() scanned every line for ^#{1,6}\s+ with no fence state, so a
check-in that quotes the four-heading contract in a fenced block was graded as
carrying all four headings while carrying none as structure. queue_index.py has
skipped fences since it was written; the check-in reader never did.

Pre-fix on the quoted fixture: headings_missing == [] (false green).
Post-fix: ['next','ask']. Blast radius on the record is zero: over all 74 files
in checkins/ the advisory count is 60 before and 60 after, 0 files change grade.

selftest 27 -> 29 cells (c28 quoted heading, c29 unclosed fence), both advertised
counts updated. verify.py 3/3 rc 0 (sweep 14 tools, 14 OK, 0 fatal).

tools/checkin_check.py

@@ -45,7 +45,9 @@ RULES IMPLEMENTED (stated, not implied)
                  tree after the archive does, so grading history by it would
                  report 57 of 70 files faulty at `c374a0a` -- noise that buries
                  the 25 name faults. It is printed, counted, and carried in
-                 --json, and the summary says which rule it is.
+                 --json, and the summary says which rule it is. A heading inside
+                 a fenced block is quoted material, not structure, and does not
+                 count (the same fence rule `queue_index.py` applies).
   A2 GAP         a day inside a handle's own span with no file, and days since
                  the newest file against --today. ADVISORY, per the table's own
                  words: "A lane that stops churning is a lane that needs a
@@ -66,7 +68,7 @@ USAGE:
   python3 checkin_check.py --repo /root/troupe-standup
   python3 checkin_check.py --repo . --gaps --json /tmp/checkins.json
   python3 checkin_check.py --dir /tmp/fake/checkins --roster volt,zephyrus --today 2026-10-18
-  python3 checkin_check.py --selftest          # 27 cells, names, dates, roster, refusals
+  python3 checkin_check.py --selftest          # 29 cells, names, dates, roster, refusals
 """
 from __future__ import annotations
 
@@ -81,6 +83,8 @@ NAME_RE = re.compile(r"^(\d{4})-(\d{2})-(\d{2})-([a-z][a-z0-9]*)\.md$")
 AMBIENT_RE = re.compile(r"^(\d{4})-(\d{2})-(\d{2})-(.+)\.md$")
 ROSTER_HANDLE_RE = re.compile(r"^[a-z][a-z0-9]*$")
 HEADING_RE = re.compile(r"^#{1,6}\s+(.*\S)\s*$")
+# A fenced block is quoted material, never structure (see headings_missing).
+FENCE_RE = re.compile(r"^\s*(```|~~~)")
 # The four headings are matched on the heading's own first word, case-folded.
 WANT_HEADINGS = ("did", "blocked", "next", "ask")
 
@@ -197,8 +201,23 @@ def read_text(path: str) -> str:
 
 
 def headings_missing(text: str):
-    seen = set()
+    """The four contract words this file does NOT use as a heading.
+
+    A fenced block is quoted material, not structure: a check-in that shows the
+    contract itself (``` ## Did / ## Blocked / ## Next / ## Ask ```) was graded
+    as carrying all four while carrying none. `queue_index.py` already skips
+    fences for the same reason; this reader now does too. Measured over the 74
+    files at `331927f`: 0 files change grade (60 of 74 advisory-missing before
+    and after), so the fix is a sound for the quoted-heading form, not a
+    re-reading of the archive.
+    """
+    seen, in_fence = set(), False
     for line in text.splitlines():
+        if FENCE_RE.match(line):
+            in_fence = not in_fence
+            continue
+        if in_fence:
+            continue
         m = HEADING_RE.match(line)
         if m:
             seen.add(m.group(1).split()[0].strip("*_`:").lower())
@@ -557,7 +576,18 @@ def selftest():
         cell("c26 a malformed --since refuses at rc 2, never 1",
              main(["--dir", ck, "--roster", "volt", "--since", "16-10-2026"]) == 2)
 
-    print(f"selftest: 27 cells, {27 - len(bad)} passed, {len(bad)} failed")
+    # The quoted-heading form: a fenced block is material, not structure. Both
+    # cells drive the real reader on inline text, not a fixture line number.
+    quoted = ("# 2026-10-17 -- volt\n\n## Did\nx\n\n## Blocked\nx\n\n"
+              "```\n## Next\ny\n## Ask\nno\n```\n")
+    cell("c28 a heading inside a fenced block is not a heading",
+         headings_missing(quoted) == ["next", "ask"],
+         str(headings_missing(quoted)))
+    cell("c29 an unclosed fence quotes to end of file, and says so",
+         headings_missing("## Did\nx\n```\n## Blocked\n## Next\n## Ask\n")
+         == ["blocked", "next", "ask"])
+
+    print(f"selftest: 29 cells, {29 - len(bad)} passed, {len(bad)} failed")
     return 1 if bad else 0