Identify built-in generation preparation failures

docs/roadmap/implementation.md

@@ -198,6 +198,11 @@ fails with the public invalid-request category and zero dispatch. Existing
 provider rejection, missing-key, capacity, injected, and cancellation tests
 retain their respective outcomes.
 
+Completion: built-in preparation failures carry direct error and evidence
+markers; diagnostics return invalid-request errors before dispatch. Generation,
+use-case, and root tests pass on Go 1.27.3, including the previously deferred
+injected-client classification cases.
+
 ## Stage 7: Bound Authentication Recognition And Report Overflow
 
 **Catalog:** 2. **Files:** current authentication probe, public/domain smoke reasons.