Build provider requests directly as payloads

docs/roadmap/implementation.md

@@ -97,6 +97,11 @@ where fixture migration remains. No production construction supplies the removed
 
 ## Stage 2: Encode One Root Wire Representation
 
+**Completed:** Requests now build the provider payload directly, with structured
+dispatch evidence derived from that payload. Go 1.27.3 `go test ./internal/llm
+./internal/generation` passed, including mapping, presence, payload freezing,
+session, structured-output, and encoding-failure tests.
+
 **Finding:** 2. **Files:** `internal/llm/openai_compatible_client.go` and request-mapping tests.
 
 1. Replace the root `domain request -> openAIChatRequest -> map` sequence with