Remove legacy manifest provenance decoding

docs/roadmap/remediation.md

@@ -1,6 +1,6 @@
 # Audita v2 and ConfigKit Migration Review Remediation
 
-Status: Pending.
+Status: Complete.
 
 Reviewed `83eaa96` through `fae18bf` against the approved clean-cutover decisions,
 [feature roadmap](audita.md), and [implementation plan](implementation.md).
@@ -46,7 +46,14 @@ Required remediation:
 
 ## 2. Remove the unapproved manifest compatibility decoder
 
-Priority: P2. Status: Pending.
+Priority: P2. Status: Complete.
+
+Removed the permissive custom decoder; ordinary strict typed decoding now
+applies to provenance as well. Replaced historical-acceptance coverage with
+retired/unknown-field rejection tests, all of which failed before removal.
+Current provenance round-trip coverage remains intact. Corrected the roadmap,
+plan, internal contract, and operator guidance for narrow backed-up migration
+without discarding execution/checkpoint state or changing resume authority.
 
 Location: `internal/manifest/manifest.go:79-89`,
 `internal/manifest/store_test.go:78`, and `docs/internal/manifest.md`'s decoding
@@ -92,6 +99,8 @@ reader. Do not treat that exception as already granted.
 
 ## Review verification
 
+The following records the original review, before remediation.
+
 - Existing `go test ./...` passed.
 - Race tests passed for subprocess, Audita, Notarius, config, stage, app, and
   manifest packages after removing the temporary reproduction.
@@ -105,6 +114,13 @@ shared named credential forwarding/redaction, a v2-only Audita subprocess
 adapter, ordinary reports as diagnostics, and versioned ordered-module polish
 evidence. No live model/provider runs were performed during this review.
 
+## Migration remediation verification
+
+Completed on 2026-09-25. Both new regressions failed before their respective
+fixes. After remediation, `go test ./...`, `go test -race ./...`,
+`go vet ./...`, `go build ./...`, documentation checks, maintained configuration
+example checks, and `git diff --check` passed. No live provider runs were needed.
+
 ## Historical completed transcription review
 
 Status: Complete.