Use explicit IDs in configuration source builders

docs/roadmap/implementation.md

@@ -384,6 +384,14 @@ tests. Other callers are migrated in later stages.
 Validation: the public construction/source-builder tests demonstrate the new
 input shape and ownership. Do not add map compatibility or builder-only ID rules.
 
+Completion: profile and backend builders now accept ordered explicit-ID slices,
+preserve duplicates and owned values, and encode profile inheritance by sibling
+identity. Migrated their owning construction callers and added focused tests
+for order, copying, duplicate rejection, and real profile inheritance. Validation
+passed: the isolated source-builder contract tests and `go build .` on Go 1.27.0,
+formatting, and `git diff --check`. The full root test package remains deferred
+until later callers are converted to the new signatures.
+
 ## Stage 9: Remove Internal Prompt-Version Propagation
 
 Scope: domain values, prompt requirement snapshots, hashes, use cases, and