Expose transport and malformed generation errors

docs/consumers/pkg-promptkit.md

@@ -558,6 +558,14 @@ disclosure policy. Promptkit does not assign retry or presentation behavior.
 The [`GenerationError` GoDoc](../../generation_error.go) owns the exact typed
 error contract.
 
+Generation failures also match `ErrTransport` when the built-in HTTP request
+fails, or `ErrMalformedResponse` when a successful provider response cannot be
+decoded or an injected client returns a nil successful response. Both retain
+`ErrLLMGenerate`; transport failures retain their original causes for
+`errors.Is` and `errors.As`. Caller cancellation and deadlines retain their
+standard context identities. Arbitrary injected-client errors retain their own
+identities without Promptkit guessing a failure category from their text.
+
 ## Application Boundary
 
 Promptkit is an importable library. It does not own a command, inbound HTTP