Document resumable transcription and replay

docs/internal/stage-transcribe.md

@@ -14,12 +14,19 @@ Generate raw per-speaker transcripts from prepared audio using WhisperX.
 
 ## Key Behavior
 
-- discovers prepared audio from manifest inputs or canonical audio directory.
-- derives the transcript identity from the prepared `.flac` filename.
-- dispatches one WhisperX request per prepared file through a bounded errgroup.
-- validates each output as JSON.
-- writes run-local outputs then materializes canonical transcript outputs only
-  after every planned request succeeds.
+- discovers prepared audio from manifest inputs or the canonical audio
+  directory and derives each speaker identity from its `.flac` filename.
+- hashes the current audio and reconciles it with the versioned per-speaker
+  completion collection before starting HTTP work.
+- reuses only records whose audio identity, observable WhisperX semantics,
+  canonical output location, JSON, checksum, and size remain current.
+- durably checkpoints the reconciled collection before dispatch, then sends
+  only missing or obsolete speakers through the bounded worker group.
+- validates each successful run-local response, rechecks the audio bytes,
+  materializes the canonical raw transcript, and checkpoints that speaker
+  before accepting another completion.
+- rebuilds aggregate stage outputs in stable speaker order from the complete
+  current collection, including records produced by earlier invocations.
 
 ## Invariants
 
@@ -28,21 +35,44 @@ Generate raw per-speaker transcripts from prepared audio using WhisperX.
 - output path returned by adapter must match requested output path.
 - an empty adapter result path means the requested path; adapters cannot select
   an alternate destination.
-- each successful output is validated before stage success, and cancellation or
-  incomplete dispatch cannot be reported as a successful result.
+- candidate collection construction, manifest save, and installation into live
+  state are serialized. Expensive hashing and HTTP work remain outside that
+  critical section.
+- a canonical file has no completion authority until its manifest checkpoint
+  succeeds. A save failure preserves the last successfully committed
+  collection for ordinary retry.
+- each successful output is validated before its checkpoint, and cancellation,
+  incomplete dispatch, or a failed aggregate save cannot be reported as
+  aggregate stage success.
+- removed audio inputs are omitted from the current collection and aggregate
+  output list; reconciliation does not delete arbitrary transcript files.
+- merge cannot consume a partial versioned collection: it requires transcribe
+  aggregate success and an exact match between current speaker records and
+  declared aggregate outputs.
 
 ## Resume Evidence
 
-Transcribe records a versioned semantic-configuration fingerprint containing
-the Narratio-visible WhisperX service URL and recognition language. Changes to
-either rerun transcription and stale its fixed descendants while leaving
-prepare reusable. Retry count/delay, concurrency, timeout, credentials, and
-diagnostic locations are operational and do not change this evidence.
+Each completed speaker record binds the speaker ID, session-relative audio
+path, streamed audio checksum and size, the Narratio-visible WhisperX service
+URL and recognition language, and the canonical transcript path, checksum,
+size, and producer run. Changed audio bytes select that speaker for replacement;
+a changed URL or language selects every speaker. Either case stales fixed
+descendants through the normal runner decision. Retry count/delay, concurrency,
+timeout, credentials, and diagnostic locations are operational and do not
+change this evidence.
+
+An ordinary retry reuses every valid speaker checkpoint even when aggregate
+transcribe status is failed, running, or stale. `--force` first durably replaces
+the collection with an empty versioned collection, so a later ordinary retry
+cannot resurrect pre-force results; speakers checkpointed by that forced
+attempt remain reusable.
 
 WhisperX models or private service configuration not exposed by Narratio's
 adapter contract cannot be fingerprinted; use `--force` after changing them.
-An existing successful transcribe record without evidence reruns once when
-selected.
+An older aggregate-only transcribe record has no trustworthy audio-to-output
+binding. When transcribe is next selected, every current speaker is therefore
+generated once and recorded in the versioned collection; later invocations can
+reuse it normally.
 
 ## Related Contracts And Tests
 
@@ -51,6 +81,9 @@ selected.
 - [Configuration](../config.md#pipeline) owns concurrency and other
   operator-selected values.
 - Implementation and tests: `internal/stage/transcribe.go`,
+  `internal/stage/transcribe_reconciliation.go`,
+  `internal/stage/transcribe_execution_state.go`,
+  `internal/stage/transcribe_resume.go`,
   `internal/stage/transcribe_test.go`,
-  `internal/stage/semantic_contracts_initial.go`, and
-  `internal/stage/semantic_contracts_initial_test.go`
+  `internal/stage/transcribe_reconciliation_test.go`, and
+  `internal/stage/transcribe_checkpoint_test.go`