fix(cases): tolerant case_number lookup so agents see case documents

Reported: an agent claimed the case had no documents because document_list
returned empty — but the documents exist. Root cause: get_case_by_number did
an exact `WHERE case_number = $1`, so any formatting variant of the number
silently failed to resolve. Verified on 8137-24 (9 docs): "8137/24",
"ערר 8137-24", leading/trailing space, and "בל\"מ 8126/03/25" all returned
"תיק לא נמצא", which the agent read as "no documents" and went blind.

Add _normalize_case_number (strip leading proceeding-type prefix to the first
digit, trim, unify '/'→'-') and a normalized fallback in the lookup query
(exact match preferred via ORDER BY). One fix covers every case_number-scoped
tool (document_list, extract_references, search_case_documents, get_claims,
drafting, ...). Bogus numbers still correctly resolve to "not found". (#58)

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

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

@@ -5,6 +5,7 @@ from __future__ import annotations
 import asyncio
 import json
 import logging
+import re
 from datetime import date
 from uuid import UUID, uuid4
 
@@ -1192,11 +1193,38 @@ async def get_active_draft_path(case_id: UUID) -> str | None:
     return row["active_draft_path"] if row else None
 
 
+def _normalize_case_number(s: str) -> str:
+    """Canonicalise a case number for tolerant lookup.
+
+    Agents receive the number in many shapes — from a Paperclip issue
+    title ("ערר 8137/24"), with a slash instead of a dash, padded, or with
+    surrounding whitespace. Stored values are bare ("8137-24"). Without
+    this, get_case_by_number's exact match silently fails and the agent
+    concludes the case has no documents (see #58). Strategy: drop any
+    leading proceeding-type prefix (everything before the first digit),
+    trim, and unify '/' → '-'.
+    """
+    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)
     async with pool.acquire() as conn:
+        # Exact match first (fast path + preferred); fall back to a
+        # separator/prefix-normalised comparison so common formatting
+        # variants still resolve to the right case. See #58.
         row = await conn.fetchrow(
-            "SELECT * FROM cases WHERE case_number = $1", case_number
+            """SELECT * FROM cases
+               WHERE case_number = $1
+                  OR replace(btrim(case_number), '/', '-') = $2
+               ORDER BY (case_number = $1) DESC, created_at
+               LIMIT 1""",
+            case_number, norm,
         )
     if row is None:
         return None