fix(dispatch): bucket failures by geo cell while the backend omits zone_id

Every booking.assignment_failed observed in production carries no zone_id, so
the per-zone failure counter and the once-a-day alert limit collapsed into a
single global "unknown" bucket — one alert per day for the whole country.

zone_key() prefers the backend's zone_id and falls back to a coarse lat/lon
grid cell (1 dp, ~11 km, DISPATCH_GEO_BUCKET_DP). The failure reason is now
logged too.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012AJLYcbTHCe45fyFnMfEin

agents/dispatch_agent.py

@@ -47,6 +47,27 @@ MILER_UNAVAILABLE_STATUSES = {"break", "offline", "busy", "onbreak", "off_duty",
 
 AVAILABLE, UNAVAILABLE, UNKNOWN = "available", "unavailable", "unknown"
 
+# The Go backend does not yet send zone_id on booking.assignment_failed (every
+# event observed carries none). Without a fallback, every failure in the country
+# shares the single "unknown" bucket, so the per-zone counter and the once-a-day
+# alert limit would collapse into one global bucket. Derive a coarse grid cell
+# from the pickup coordinates instead: 1 decimal place is ~11 km, about the size
+# of a delivery zone. Real zone_ids, once sent, take precedence.
+GEO_BUCKET_DP = int(os.getenv("DISPATCH_GEO_BUCKET_DP", "1"))
+
+
+def zone_key(zone_id, lat, lon) -> str:
+    """Stable bucket for counting failures: the backend's zone_id when present,
+    else a coarse lat/lon grid cell, else 'unknown'."""
+    if zone_id and str(zone_id).lower() not in ("", "unknown", "none", "null"):
+        return str(zone_id)
+    if lat is not None and lon is not None:
+        try:
+            return f"geo:{round(float(lat), GEO_BUCKET_DP)},{round(float(lon), GEO_BUCKET_DP)}"
+        except (TypeError, ValueError):
+            pass
+    return "unknown"
+
 
 class DispatchAgent(SpecializedAgent):
     """
@@ -274,11 +295,15 @@ class DispatchAgent(SpecializedAgent):
         try:
             data = json.loads(msg.data.decode())
             booking_id = data.get("booking_id")
-            zone_id    = data.get("zone_id", "unknown")
             lat        = data.get("lat")
             lon        = data.get("lon")
+            # Falls back to a coarse geo cell while the backend omits zone_id.
+            zone_id    = zone_key(data.get("zone_id"), lat, lon)
 
-            logger.warning(f"[DISPATCH] booking.assignment_failed — booking={booking_id} zone={zone_id}")
+            logger.warning(
+                f"[DISPATCH] booking.assignment_failed — booking={booking_id} zone={zone_id} "
+                f"reason={data.get('reason')!r}"
+            )
 
             facts, count = await self._gather_assignment_facts(zone_id, lat, lon)
             logger.info(f"[DISPATCH] booking={booking_id} context facts: {facts}")

tests/test_dispatch_agent.py

@@ -288,6 +288,29 @@ class TestRateLimitAndSinks(unittest.IsolatedAsyncioTestCase):
         self.assertEqual(payload["proposed_action"], "escalate")
 
 
+class TestZoneKey(unittest.IsolatedAsyncioTestCase):
+    """The backend sends no zone_id today; without a fallback every failure in
+    the country shares one bucket and the daily alert limit becomes global."""
+
+    async def test_real_zone_id_wins(self):
+        from agents.dispatch_agent import zone_key
+        self.assertEqual(zone_key("hyderabad", 17.4, 78.4), "hyderabad")
+
+    async def test_missing_zone_falls_back_to_geo_cell(self):
+        from agents.dispatch_agent import zone_key
+        self.assertEqual(zone_key(None, 11.0182714, 76.9677744), "geo:11.0,77.0")
+        self.assertEqual(zone_key("unknown", 11.0182714, 76.9677744), "geo:11.0,77.0")
+
+    async def test_distant_pickups_get_different_buckets(self):
+        from agents.dispatch_agent import zone_key
+        self.assertNotEqual(zone_key(None, 11.01, 76.96), zone_key(None, 17.44, 78.39))
+
+    async def test_no_zone_and_no_coords_is_unknown(self):
+        from agents.dispatch_agent import zone_key
+        self.assertEqual(zone_key(None, None, None), "unknown")
+        self.assertEqual(zone_key("unknown", "bad", "coords"), "unknown")
+
+
 class TestBindConsumer(unittest.IsolatedAsyncioTestCase):
     async def test_binds_to_discovered_stream_without_creating(self):
         js = FakeJS(stream_name="TRACKING")