feat(ingest): write-time canonical case_number normalization (GAP-06, FU-2a)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

mcp-server/src/legal_mcp/services/db.py

@@ -1155,7 +1155,7 @@ async def create_case(
                hearing_date, notes, expected_outcome,
                practice_area, appeal_subtype, proceeding_type)
                VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11, $12, $13, $14, $15)""",
-            case_id, case_number, title,
+            case_id, _canonical_case_number(case_number), title,
             json.dumps(appellants or []),
             json.dumps(respondents or []),
             subject, property_address, permit_number, committee_type,
@@ -1211,6 +1211,21 @@ def _normalize_case_number(s: str) -> str:
     return s.strip().replace("/", "-")
 
 
+def _canonical_case_number(s: str) -> str:
+    """Canonical write-time form per X1 §1: trim · prefix-strip · '/'→'-'.
+
+    Deterministic and format-only — does NOT add or remove a month segment.
+    Used at the write boundary for identifier-keyed corpora (internal
+    committee decisions, active cases). NOT for external precedents, whose
+    canonical identifier is the full citation.
+    """
+    s = (s or "").strip()
+    m = re.search(r"\d", s)
+    if m:
+        s = s[m.start():]
+    return s.strip().replace("/", "-")
+
+
 async def get_case_by_number(case_number: str) -> dict | None:
     pool = await get_pool()
     norm = _normalize_case_number(case_number)
@@ -2647,6 +2662,7 @@ async def create_internal_committee_decision(
     filed against an existing appeal with the same number).
     """
     pool = await get_pool()
+    case_number = _canonical_case_number(case_number)
     tags_json = json.dumps(subject_tags or [], ensure_ascii=False)
     async with pool.acquire() as conn:
         existing = await conn.fetchrow(