Record empty import evidence completion

docs/roadmap/implementation.md

@@ -1,6 +1,6 @@
 # Implementation Plan: Import Discovery and Dependency-Ready Ordering
 
-Status: Stages 1–14 complete; 5 implementation stages remain.
+Status: Stages 1–15 complete; 4 implementation stages remain.
 
 ## Authority, baseline, and execution
 
@@ -567,6 +567,15 @@ An error after a prior empty optional declaration retains that established
 evidence, but does not fabricate later outcomes. Mutating query results cannot
 alter subsequent snapshots or another load.
 
+Completion: implemented in commit `e433988` (`Retain empty optional import
+selection evidence`). Verified with focused evidence tests,
+`go test ./internal/engine -count=1`, `go test -race ./internal/engine`,
+`go test . -count=1`, `go vet ./...`, `go build ./...`, and
+`git diff --check`. Source-local evidence survives composition, nested item
+placement, underlays, overlays, resolution entry, final publication, and failed
+loads; the known prompt-catalog ordering expectation updates remain assigned to
+Stage 18. Stages 16–19 remain.
+
 ## Stage 16 — Expose defaults and inspection through the public facade
 
 Add root-owned declarations from this plan, `ImportDefaults` fields on ordinary