fix: surface Spotify quota exhaustion

Co-Authored-By: Claude <noreply@anthropic.com>

backend/app/pipeline/orchestrator.py

@@ -38,6 +38,8 @@ from app.ports.protocols import (
 RERANK_FALLBACK_CODE = "rerank_fallback"
 RERANK_FALLBACK_MESSAGE = "Ranking output was invalid, so grounded results are shown instead."
 RERANK_FALLBACK_JUSTIFICATION = "Selected as a grounded match for your request."
+QUOTA_ERROR_CODE = "quota_exhausted"
+QUOTA_ERROR_MESSAGE = "Spotify's Development Mode quota is temporarily exhausted."
 
 
 class _TrackSelection:
@@ -140,10 +142,8 @@ class RecommendationPipeline:
             return
         except CatalogQuotaExhaustedError:
             yield PipelineErrorEvent(
-                code="quota_exhausted",
-                message=(
-                    "Spotify request quota was exhausted before recommendations could be prepared."
-                ),
+                code=QUOTA_ERROR_CODE,
+                message=QUOTA_ERROR_MESSAGE,
             )
             return
         except SpotifyError:
@@ -158,9 +158,16 @@ class RecommendationPipeline:
             candidate_count=len(intent.candidates),
         )
 
-        pool = await self._grounded_pool(
-            session_id, catalog, intent, taste, deadline_at, seeded_pool
-        )
+        try:
+            pool = await self._grounded_pool(
+                session_id, catalog, intent, taste, deadline_at, seeded_pool
+            )
+        except CatalogQuotaExhaustedError:
+            yield PipelineErrorEvent(
+                code=QUOTA_ERROR_CODE,
+                message=QUOTA_ERROR_MESSAGE,
+            )
+            return
         if not pool:
             yield PipelineErrorEvent(
                 code="no_grounded_results",
@@ -209,6 +216,8 @@ class RecommendationPipeline:
             self.settings.rerank_count + self.settings.rerank_pool_buffer,
             deadline_at,
         )
+        if not result.tracks and result.metrics.did_exhaust_quota:
+            raise CatalogQuotaExhaustedError
         if result.tracks:
             self.last_pools[session_id] = result.tracks
         return result.tracks