Make WhisperX uploads replayable

docs/roadmap/implementation.md

@@ -1,6 +1,6 @@
 # Implementation Plan: Speaker Checkpoints and Replayable Uploads
 
-Status: Implementation in progress; Stages 1-4 complete.
+Status: Implementation in progress; Stages 1-5 complete.
 
 ## Scope and Instructions
 
@@ -291,7 +291,18 @@ expose incomplete transcripts downstream.
 
 ## Stage 5: Implement Replayable Streaming Multipart Bodies
 
-Status: Pending.
+Status: Complete.
+
+Completion marker (2026-09-22): Replaced the producer-goroutine/pipe upload
+with bounded standard-library multipart framing and independently opened,
+pull-based streaming bodies shared by the initial request and `GetBody`.
+Bodies are tracked, idempotently closed, canceled with their attempt context,
+and retain genuine read/close failures without treating an intentionally
+abandoned original as a replay failure. Added focused coverage for identical
+framing, partial-read restart, simultaneous handles, source failures, and
+blocked-reader release. Verified with `go test ./internal/adapters/whisperx`,
+`go test -race ./internal/adapters/whisperx` (including ten repeated runs), and
+`git diff --check`.
 
 Preparation: `internal/adapters/whisperx/http.go`, `http_test.go`,
 `docs/integrations/whisperx.md`, and the installed Go net/http Request/GetBody