Document smoke-test diagnostics

docs/internal/generation.md

@@ -41,9 +41,20 @@ original error chain. This keeps injected attempt classifications consistent
 with terminal observations without parsing diagnostic text or retrying injected
 clients.
 
+The diagnostic path uses the same private attempt and retry implementation as
+ordinary generation. It retains invocation-local transport, response,
+generation, usage, capacity-wait, and retry-delay evidence before normal
+result-discard and cancellation checks. This evidence is returned to diagnostic
+orchestration; it is not added to public `ExecutionEvent` values or ordinary
+observer accounting. The [model-client document](llm.md) describes the
+transport-observation boundary, and the root
+[`SmokeTestReport` GoDoc](../../smoke_diagnostics.go) owns report semantics.
+
 Focused coordinator tests use controlled transport and wait functions. They
 cover eligibility, exhaustion, cancellation, backoff, request freezing, permit
-release, and the injected-client path. The capacity manager tests own permit
+release, and the injected-client path. The
+[evidence tests](../../internal/generation/evidence_test.go) own diagnostic
+attempt retention and retry evidence. The capacity manager tests own permit
 acquisition and idempotent release. Public
 [integration tests](../../reliable_execution_contract_test.go) cover retry,
 repair, observation, frozen prepared execution, and shared-backend behavior