Translate LLM backend capacity failures

docs/policy/architecture.md

@@ -177,7 +177,8 @@ individual modules.
 The application-wide LLM scheduler bounds actual provider calls independently
 of framework worker limits. Every LLM-backed module, retry, and validator uses
 the single injected scheduled client, including work performed by overlapping
-lanes.
+lanes. Provider runtime adapters may enforce a narrower backend-specific limit
+beneath this mandatory application-wide scheduler.
 
 ## Configuration And Provenance