feat(mcp): FU-14 GAP-45 — extraction_status (חשיפת תור-החילוץ הסמוי)

INV-TOOL4 (visibility / persistence). תור בקשות-החילוץ (metadata/halacha) נשמר
ב-case_law.{metadata,halacha}_extraction_requested_at ומרוקן ע"י
precedent_process_pending — אבל לא היה כלי לראות את עומק-התור.

נוסף:
- db.extraction_queue_status() — count + גיל הבקשה הוותיקה לכל kind (read-only).
- plib.extraction_status() — tool wrapper (envelope _ok/_err).
- רישום extraction_status ב-server.py ליד precedent_process_pending.
- precedent_process_pending קיבל _clamp_limit (עקביות עם GAP-53).

תוספתי, read-only, אפס שבירה. עודכנו X9 (INV-TOOL4 ✅) ו-gap-audit (GAP-45 ✅).
py_compile עבר על 3 קבצי הקוד.

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

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

@@ -4332,6 +4332,31 @@ async def list_pending_extraction_requests(
     return out
 
 
+async def extraction_queue_status() -> dict:
+    """Pending-extraction queue depth per kind (INV-TOOL4 visibility / GAP-45).
+
+    Surfaces the otherwise-hidden queue that ``process_pending_extractions``
+    drains: how many case_law rows still carry a metadata/halacha extraction
+    request, and the age of the oldest one. Read-only — does not drain.
+    """
+    pool = await get_pool()
+    async with pool.acquire() as conn:
+        meta = await conn.fetchrow(
+            "SELECT COUNT(*) AS n, MIN(metadata_extraction_requested_at) AS oldest "
+            "FROM case_law WHERE metadata_extraction_requested_at IS NOT NULL"
+        )
+        hal = await conn.fetchrow(
+            "SELECT COUNT(*) AS n, MIN(halacha_extraction_requested_at) AS oldest "
+            "FROM case_law WHERE halacha_extraction_requested_at IS NOT NULL"
+        )
+
+    def _fmt(r: dict) -> dict:
+        oldest = r["oldest"]
+        return {"pending": r["n"], "oldest_request": oldest.isoformat() if oldest else None}
+
+    return {"metadata": _fmt(meta), "halacha": _fmt(hal)}
+
+
 async def clear_extraction_request(
     case_law_id: UUID, kind: str = "metadata",
 ) -> None: