feat(brief): parse optional Depends on / Conflicts with fields (#36)

Add depends_on() / conflicts_with() accessors over the existing lenient
field parser, plus the two optional brief-template fields. Parser-first
half of #36: safe on its own because unknown bullet labels are already
ignored, so existing briefs and the scheduler are unaffected until the
DAG-gated dispatch change lands.

Ids are normalised to bare form (strip leading '#' and the issue_ prefix)
to match how cfg.bundle(id) keys bundles, so a brief may write #36 / 36 /
issue_36 interchangeably.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: eduralph

template/src/pdca_harness/brief.py

@@ -53,3 +53,33 @@ def test_files(brief_path: Path) -> list[Path]:
     # Pull anything that looks like a path token out of the field value.
     tokens = re.findall(r"[\w./-]+\.\w+", raw)
     return [Path(t) for t in tokens]
+
+
+def depends_on(brief_path: Path) -> list[str]:
+    """Issue ids this bundle must wait for — each must be COMPLETE before it runs.
+
+    The optional ``- **Depends on:** <id>[, <id>…]`` field (docs 09). Absent ⇒
+    ``[]`` ⇒ today's sort-by-name scheduling, unaffected.
+    """
+    return _id_list(field(brief_path, "depends on", "depends_on"))
+
+
+def conflicts_with(brief_path: Path) -> list[str]:
+    """Issue ids that must never run in the same concurrent wave as this bundle.
+
+    The optional ``- **Conflicts with:** <id>[, <id>…]`` field (docs 09): a pair
+    that edits a shared resource and so cannot be co-scheduled across lanes.
+    """
+    return _id_list(field(brief_path, "conflicts with", "conflicts_with"))
+
+
+def _id_list(raw: str) -> list[str]:
+    """Issue ids out of a comma/space-separated field value, normalised to bare ids.
+
+    Tolerates a leading ``#`` and the ``issue_`` bundle prefix so a brief may write
+    ``#36`` / ``36`` / ``issue_36`` interchangeably; matches how ``cfg.bundle(id)``
+    keys bundles. Mirrors :func:`test_files`' tokenise-the-value approach.
+    """
+    if not raw:
+        return []
+    return [t.lstrip("#").removeprefix("issue_") for t in re.findall(r"#?[\w./-]+", raw)]

template/templates/brief.md.tpl

@@ -14,6 +14,8 @@
   satisfy this by guarding a single module? If yes, it's the narrow symptom-sentence —
   widen it. Omit only for non-structural behavioural bug fixes (principles.md §1.1).>
 - **Repo + branch target:** <owner/repo> @ <branch>   (resolve here at Plan — do not leave to Do)
+- **Depends on:** <id>[, <id>…]   (optional — batch/lane scheduling waits until these bundles are COMPLETE before this one runs; docs 09)
+- **Conflicts with:** <id>[, <id>…]   (optional — never co-schedule these in the same concurrent wave, e.g. they edit a shared file; docs 09)
 - **Surfaces:** <where the change is observable — `gui` (touches the frontend / an E2E
   through the app is needed), `data` (backend/logic only), or `both`. Drives which
   runtime gates apply (e.g. an E2E gate runs only when this is `gui`). Optional.>

template/tests/test_brief.py

@@ -37,5 +37,33 @@ def test_colon_inside_bold_does_not_leak(self) -> None:
             self.assertFalse(val.startswith("*"), val)
 
 
+class OrderingFields(unittest.TestCase):
+    """The optional Depends on / Conflicts with fields (docs 09, issue #36)."""
+
+    def _brief(self, body: str) -> Path:
+        f = Path(tempfile.mkdtemp()) / "brief.md"
+        f.write_text(body, encoding="utf-8")
+        return f
+
+    def test_depends_on_parses_comma_and_space_separated_ids(self) -> None:
+        f = self._brief("- **Depends on:** #36, 11 issue_42\n")
+        # leading '#' and the issue_ prefix are both normalised to bare ids
+        self.assertEqual(brief.depends_on(f), ["36", "11", "42"])
+
+    def test_conflicts_with_parses_list(self) -> None:
+        f = self._brief("- **Conflicts with:** C1, T1\n")
+        self.assertEqual(brief.conflicts_with(f), ["C1", "T1"])
+
+    def test_absent_field_is_empty_list(self) -> None:
+        f = self._brief("- **Slug:** no-ordering\n")
+        self.assertEqual(brief.depends_on(f), [])
+        self.assertEqual(brief.conflicts_with(f), [])
+
+    def test_empty_value_is_empty_list(self) -> None:
+        f = self._brief("- **Depends on:**\n- **Conflicts with:** \n")
+        self.assertEqual(brief.depends_on(f), [])
+        self.assertEqual(brief.conflicts_with(f), [])
+
+
 if __name__ == "__main__":
     unittest.main()