Separate prompt and target capture

docs/roadmap/implementation.md

@@ -650,6 +650,11 @@ on Go 1.27.3; the extracted checks preserve their existing paths and rules.
 input metadata, inspection, and execution-selection tests keep their behavior.
 Update focused source/internal descriptions without duplicating format policy.
 
+Completion: prompt inputs, messages, and output contracts are captured separately
+before final definition assembly, and backend/profile construction is isolated
+with presence handling intact. Configuration, prompt, engine, and focused public
+tests pass on Go 1.27.3; the internal source description is updated.
+
 ## Stage 25: Replace Parallel Attempt Returns With A Result Value
 
 **Catalog:** 25, attempt boundary. **Files:** generation coordinator and tests.