fix(implement): count checkbox markers outside code fences only

The checklist gate counted every `- [ ]` / `- [x]` line in every checklist
file, fenced blocks included. A checklist that documents the checkbox format
with an example fence therefore reported unchecked items nobody can ever tick,
and /speckit-implement stops on a non-zero unchecked count -- so writing down
the format blocked implementation.

/speckit-clarify already scopes its scan to markers outside code fences, so
this was also the two commands disagreeing about what a checklist item is.
They now state the same rule.

Closes #4272

Author: ntdatt812

templates/commands/implement.md

@@ -58,10 +58,11 @@ You **MUST** consider the user input before proceeding (if not empty).
    - `checklists/requirements.md` is the built-in spec-quality checklist maintained by `__SPECKIT_COMMAND_SPECIFY__` and `__SPECKIT_COMMAND_CLARIFY__`; custom checklists generated by `__SPECKIT_COMMAND_CHECKLIST__` are reviewer-owned requirements-quality review artifacts
    - For custom checklists, `[x]` means the reviewer determined the requirements-quality criterion is satisfied; it does NOT mean implementation work is complete
    - Scan all checklist files in the checklists/ directory
+   - Count only checkbox lines **outside of code fences**, the same rule `__SPECKIT_COMMAND_CLARIFY__` applies. A checklist that documents the checkbox format inside a fence is showing an example, not tracking work, and counting those examples blocks implementation on items nobody can ever tick
    - For each checklist, count:
-     - Total items: All lines matching `- [ ]` or `- [X]` or `- [x]`
-     - Checked items: Lines matching `- [X]` or `- [x]`
-     - Unchecked items: Lines matching `- [ ]`
+     - Total items: All lines matching `- [ ]` or `- [X]` or `- [x]` outside code fences
+     - Checked items: Lines matching `- [X]` or `- [x]` outside code fences
+     - Unchecked items: Lines matching `- [ ]` outside code fences
    - Create a status table:
 
      ```text

tests/unit/test_checklist_scan_contract.py

@@ -0,0 +1,58 @@
+"""Every command that scans checkbox markers must say it skips code fences.
+
+A checklist is free to *document* the checkbox format inside a fenced block. Counting
+those example markers reports items nobody can tick, and `/speckit-implement` treats a
+non-zero unchecked count as a reason to stop — so an example fence blocks implementation
+(#4272). `/speckit-clarify` already scoped its scan to markers outside code fences; this
+keeps the two commands from drifting apart again, and holds any future command that
+starts counting markers to the same rule.
+"""
+
+from __future__ import annotations
+
+import re
+from pathlib import Path
+
+import pytest
+
+PROJECT_ROOT = Path(__file__).resolve().parent.parent.parent
+COMMAND_DIRS = [
+    PROJECT_ROOT / "templates" / "commands",
+    *sorted((PROJECT_ROOT / "presets").glob("*/commands")),
+]
+
+# The instruction that tells the agent which lines are checkbox markers. Written to catch
+# the phrasing both commands use rather than one exact sentence.
+SCAN_INSTRUCTION = re.compile(r"lines matching\s+`- \[ \]`", re.IGNORECASE)
+FENCE_EXCLUSION = re.compile(r"outside\s+(?:of\s+)?code\s+fences", re.IGNORECASE)
+
+
+def scan_instructions() -> list[tuple[Path, int, str]]:
+    """Every line in a command template that defines what counts as a checkbox marker."""
+    found: list[tuple[Path, int, str]] = []
+    for directory in COMMAND_DIRS:
+        if not directory.is_dir():
+            continue
+        for path in sorted(directory.glob("*.md")):
+            for number, line in enumerate(path.read_text(encoding="utf-8").splitlines(), start=1):
+                if SCAN_INSTRUCTION.search(line):
+                    found.append((path, number, line))
+    return found
+
+
+def test_the_contract_is_actually_stated_somewhere() -> None:
+    """Guard against the regex silently matching nothing and the test passing vacuously."""
+    assert scan_instructions(), "no command template defines a checkbox-marker scan any more"
+
+
+@pytest.mark.parametrize(
+    ("path", "number", "line"),
+    scan_instructions(),
+    ids=lambda value: value.name if isinstance(value, Path) else str(value),
+)
+def test_marker_scans_exclude_code_fences(path: Path, number: int, line: str) -> None:
+    assert FENCE_EXCLUSION.search(line), (
+        f"{path.relative_to(PROJECT_ROOT)}:{number} tells the agent to match checkbox "
+        f"markers without excluding fenced code blocks, so an example fence is counted "
+        f"as real work:\n  {line.strip()}"
+    )