Bound Weather API response diagnostics

docs/internal/collect.md

@@ -16,6 +16,10 @@ API base URL, as weather-collection setup errors and fetch failures as
 bundle-collection errors. It does not retry, persist, select reports, derive
 facts, build modules, invoke Promptkit, or notify Distributor.
 
+Fetch failures retain Weather API endpoint context but do not project upstream
+response bodies into application-facing errors. Oversized response bodies fail
+collection before source decoding.
+
 ## Application Composition
 
 `internal/app` owns the narrow `Collector` interface used by workflow tests;