feat(halacha): lighter effort for BULK queue-drain extraction (speed at scale)

xhigh is the quality sweet-spot for a single precedent but very slow at scale
(64-chunk case ≈ 20 min). Bulk queue-drains (process_pending over many
precedents) now use a lighter effort to cut wall-clock; interactive single
re-extraction keeps xhigh quality.

- config.HALACHA_BULK_EXTRACT_EFFORT (env, default 'high'; set 'medium' for max
  speed, 'xhigh' to match single).
- extract()/_extract_impl()/_extract_chunk() take an `effort` override threaded
  to claude_session.query_json; None falls back to HALACHA_EXTRACT_EFFORT (xhigh).
- process_pending_extractions(kind='halacha') passes the bulk effort; single
  reextract_halachot keeps xhigh.

Verified end-to-end (mocked LLM): _extract_chunk(effort='medium') → query_json
effort='medium'; effort=None → 'xhigh' fallback. Closes the open item in #72.

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

mcp-server/src/legal_mcp/config.py

@@ -54,6 +54,12 @@ REDIS_URL = os.environ.get("REDIS_URL", "redis://127.0.0.1:6380/0")
 # pinned.
 HALACHA_EXTRACT_MODEL = os.environ.get("HALACHA_EXTRACT_MODEL", "claude-opus-4-8")
 HALACHA_EXTRACT_EFFORT = os.environ.get("HALACHA_EXTRACT_EFFORT", "xhigh")
+# Effort for BULK queue-drain extraction (process_pending over many precedents).
+# xhigh is the quality sweet-spot for a single precedent but very slow at scale
+# (a 64-chunk case ≈ 20 min). Bulk drains use a lighter effort to cut wall-clock;
+# interactive single re-extraction keeps HALACHA_EXTRACT_EFFORT (xhigh). Tune via
+# env (set to 'xhigh' to make bulk match single, or 'medium' for max speed).
+HALACHA_BULK_EXTRACT_EFFORT = os.environ.get("HALACHA_BULK_EXTRACT_EFFORT", "high")
 # Concurrent chunks WITHIN a single extraction. Each `claude -p` @ xhigh holds
 # ~300MB RSS + heavy CPU; cross-process overlap (agent retries) on top of this
 # froze the box on 2026-05-31 (hard reboot). A global advisory lock now caps