Retain generation response evidence

docs/roadmap/implementation.md

@@ -439,6 +439,11 @@ Validate: focused `internal/llm` tests for valid/empty/malformed generation,
 non-success status, and a decoded response followed by cancellation. Reuse
 existing envelope/usage/size tests rather than reproduce their full matrices.
 
+**Completed: 2026-10-13.** Added an evidence-enabled prepared execution path
+while keeping ordinary execution on its existing HTTP path. Validation passed:
+`go test -race ./internal/llm`, `go vet ./internal/llm`,
+`go test ./...`, and `git diff --check`.
+
 ## Stage 9: Carry Evidence Through Built-In Retry Coordination
 
 Scope: `internal/generation` and shared observation usage accounting.