Add public facade value wrappers

docs/roadmap/implementation.md

@@ -323,6 +323,26 @@ Acceptance: candidate wrapper tests and engine tests pass. Run
 `go test ./internal/facade ./internal/engine` and the everyday check. Lifecycle
 entry points are added in Stage 6; do not add nonfunctional stubs here.
 
+### Completion
+
+Status: complete (2026-09-12).
+
+Created the temporary `internal/facade` package (named `configkit`) with
+root-owned `Path`, `Source`, and `Secret` wrappers; root-owned scalar and
+provenance records; explicit private conversions; `LoadError`; and
+`WriteDiagnostics`. Public fields and signatures contain only facade types.
+`Path` carries its engine value privately without text round-tripping, `Source`
+retains the engine's source value so copied reader sources preserve their shared
+claim, and the facade builds the exact-type secret binding locally. No lifecycle
+entry point or placeholder was added.
+
+Candidate tests cover semantic path distinctions, source byte snapshotting and
+copied-reader ownership, external-package type ownership and interfaces, and
+safe secret formatting/JSON. Linux validation with Go 1.26.7 passed
+`go test ./internal/facade ./internal/engine` and `./scripts/check.sh`. There
+were no deviations. The next handoff separates engine publication from its
+generic result before lifecycle delegation begins.
+
 ## Stage 5 — Separate engine publication and inspection
 
 Status: not started.