Carry evidence through built-in generation retries

docs/roadmap/implementation.md

@@ -465,6 +465,11 @@ attempt, retry-success, exhausted retries, cancellation during backoff, and
 canceled reacquisition. Check evidence retention and timing/accounting; existing
 retry tests own unchanged retry policy. Run observation tests after extraction.
 
+**Completed: 2026-10-13.** Added built-in generation attempt evidence and shared
+presence-aware usage accumulation. Validation passed: `go test -race
+./internal/generation ./internal/observation`, `go vet ./...`, `go test ./...`,
+and `git diff --check`.
+
 ## Stage 10: Retain Injected-Client Evidence Without HTTP Claims
 
 Scope: the injected branch of `internal/generation`.