B2: tolerant JSON extraction from Claude responses + graceful fallback

_extract_json_payload handles a json/JSON/bare fence, raw JSON and JSON
embedded in prose; any unparseable response or contract violation now
degrades to the deterministic scoring_service instead of raising.
Also guards the response envelope itself (content[0].text).

B3: single home for recommendation scoring

services/recommendation_service.py holds the rules; routers/stats.py and
backend/services/stats_service.py both delegate to it. Unified rules are the
union of the two old copies: same weights/threshold, substring matching
(superset of the old exact match), tolerant key aliases, health_flags rule
kept. Endpoint response contract unchanged.

Plus: Overpass circuit breaker and concurrent zone queries in geo_service -
128 sequential calls per analysis no longer each burn a connect timeout when
the host has no outbound network.

Tests: 152 -> 194 passed.

services/recommendation_service.py

@@ -0,0 +1,80 @@
+"""
+Statistical search-priority recommendation.
+
+Single home for the recommendation scoring rules (B3). Previously duplicated
+between `backend/routers/stats.py` (inline, exact-match on terrain/weather,
+plus a health_flags rule) and `backend/services/stats_service.py` (substring
+match on tolerant key aliases, no health_flags rule).
+
+The unified rules below are the union of the two: identical weights and
+threshold, substring matching (a superset of the old exact match), tolerant
+input keys, and the health_flags rule kept. This is NOT the 7-factor zonal
+scoring of `scoring_service` — it only labels a case high/normal priority.
+
+Deliberately free of any database import so both the router and the service
+layer can use it without side effects.
+"""
+from __future__ import annotations
+
+from typing import Any
+
+# Scoring weights and threshold — unchanged from both previous implementations.
+WEIGHT_YOUNG_CHILD = 20
+WEIGHT_LONG_ELAPSED = 20
+WEIGHT_RISKY_TERRAIN = 15
+WEIGHT_ADVERSE_WEATHER = 15
+WEIGHT_MULTIPLE_HEALTH_FLAGS = 15
+
+HIGH_PRIORITY_THRESHOLD = 40
+
+YOUNG_CHILD_AGE = 12
+LONG_ELAPSED_HOURS = 12
+MULTIPLE_HEALTH_FLAGS = 2
+
+RISKY_TERRAIN_TOKENS = ('лес', 'болото', 'вода')
+ADVERSE_WEATHER_TOKENS = ('дождь', 'туман', 'снег', 'ночь')
+
+HIGH_PRIORITY_TEXT = 'Высокий приоритет на прочёс и дрон'
+NORMAL_PRIORITY_TEXT = 'Стандартный приоритет поиска'
+
+
+def score_recommendation(
+    age: int | None = None,
+    elapsed_hours: int | None = None,
+    terrain: str | None = None,
+    weather: str | None = None,
+    health_flags: list[str] | None = None,
+) -> dict[str, Any]:
+    """Score a case and return {'score', 'priority', 'recommendation'}."""
+    score = 0
+
+    if age is not None and age < YOUNG_CHILD_AGE:
+        score += WEIGHT_YOUNG_CHILD
+    if elapsed_hours is not None and elapsed_hours >= LONG_ELAPSED_HOURS:
+        score += WEIGHT_LONG_ELAPSED
+    if any(token in str(terrain or '').lower() for token in RISKY_TERRAIN_TOKENS):
+        score += WEIGHT_RISKY_TERRAIN
+    if any(token in str(weather or '').lower() for token in ADVERSE_WEATHER_TOKENS):
+        score += WEIGHT_ADVERSE_WEATHER
+    if len(health_flags or []) >= MULTIPLE_HEALTH_FLAGS:
+        score += WEIGHT_MULTIPLE_HEALTH_FLAGS
+
+    is_high = score >= HIGH_PRIORITY_THRESHOLD
+
+    return {
+        'score': score,
+        'priority': 'high' if is_high else 'normal',
+        'recommendation': HIGH_PRIORITY_TEXT if is_high else NORMAL_PRIORITY_TEXT,
+    }
+
+
+def get_statistical_recommendation(case_data: dict[str, Any]) -> dict[str, Any]:
+    """Dict-based entry point, tolerant of the field aliases used across
+    the desktop / mobile / admin payloads."""
+    return score_recommendation(
+        age=case_data.get('age') if case_data.get('age') is not None else case_data.get('age_years'),
+        elapsed_hours=case_data.get('elapsed_hours'),
+        terrain=case_data.get('terrain') or case_data.get('terrain_primary'),
+        weather=case_data.get('weather') or case_data.get('precipitation'),
+        health_flags=case_data.get('health_flags'),
+    )