feat(extraction): precedent metadata via Gemini Flash + scheduled drainer

The /precedents metadata queue was stuck — 24 rows requested, nothing draining
them — and the agentic claude CLI hit error_max_turns on what is a single
structured text→JSON task (slow + flaky). Metadata extraction is bounded
extraction, the wrong fit for an agentic loop.

- gemini_session.py: query_json drop-in (gemini-2.5-flash, JSON mode, httpx —
  no new SDK dep). Reads GEMINI_API_KEY (~/.env; SoT Infisical
  nautilus:/external-apis/gemini). Host-side only — no LLM from the container.
- precedent_metadata_extractor: claude_session.query_json → gemini_session.
  Validated live: rich, accurate fields (case_name/summary/appeal_subtype/tags).
- process_pending_extractions: kind-aware cooldown — metadata 2s (Gemini, fast),
  halacha keeps 30s (Claude rate limits).
- drain_metadata_queue.py + legal-metadata-drain.config.cjs (pm2 cron */15) so
  the queue never clogs again. SCRIPTS.md.
- X8 INV-FP5 updated: per-task engine choice (Gemini=bounded metadata,
  claude_session=agentic halacha), both host-side, single canonical queue (G2).

Agentic/voice-sensitive work (writing, analysis, halacha) stays on claude_session
(Daphna's subscription). Gemini cost ≈ $0.10/1M tokens — negligible.

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

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

@@ -15,6 +15,7 @@ from __future__ import annotations
 
 import asyncio
 import logging
+import os
 from pathlib import Path
 from typing import Awaitable, Callable
 from uuid import UUID
@@ -179,6 +180,9 @@ async def reextract_halachot(
 # precedent into a 429 storm. Observed 2026-05-03: 1110/20 succeeded with 9
 # halachot, 317/10 immediately after returned silent no_halachot.
 INTER_PRECEDENT_COOLDOWN_SEC = 30
+# Metadata extraction is on Gemini (fast, high rate limits) — a brief spacer is
+# enough; the 30s above is for the Claude-backed halacha path.
+METADATA_COOLDOWN_SEC = float(os.environ.get("METADATA_COOLDOWN_SEC", "2"))
 
 # How many times to retry a precedent that came back as 'extraction_failed'
 # (i.e. >50% chunks crashed). Each retry uses a longer cooldown.
@@ -226,11 +230,14 @@ async def process_pending_extractions(kind: str = "metadata", limit: int = 20) -
             cid, effort=config.HALACHA_BULK_EXTRACT_EFFORT,
         )
 
+    # Metadata extraction runs on Gemini (high rate limits, fast) — the long
+    # cooldown is only needed for halacha (Claude/Anthropic rate limits).
+    cooldown = METADATA_COOLDOWN_SEC if kind == "metadata" else INTER_PRECEDENT_COOLDOWN_SEC
     results: list[dict] = []
     processed = 0
     for idx, row in enumerate(pending):
         if idx > 0:
-            await asyncio.sleep(INTER_PRECEDENT_COOLDOWN_SEC)
+            await asyncio.sleep(cooldown)
         cid = UUID(str(row["id"]))
         attempts = 0
         result: dict = {}