Document resumable transcription and replay

docs/troubleshooting.md

@@ -213,6 +213,100 @@ input validation.
 
 Relevant reference: [Operations: Stage Execution and Continuation Behavior](./operations.md#stage-execution-and-continuation-behavior).
 
+## Transcription retries speakers that previously finished
+
+Symptom:
+
+- an ordinary transcribe retry calls WhisperX for a speaker that appeared to
+  finish earlier; or
+- an older successful session retranscribes all speakers once after upgrade.
+
+Likely causes:
+
+- the earlier response or canonical file was not followed by a successful
+  speaker manifest checkpoint;
+- the prepared audio bytes/path, WhisperX URL, or language changed;
+- the canonical transcript is missing, unsafe, non-regular, invalid JSON, or
+  no longer matches its recorded size/checksum;
+- the previous invocation used `--force`, which durably cleared pre-force
+  speaker authority; or
+- the manifest has only legacy aggregate transcribe state and cannot bind old
+  outputs to their source audio.
+
+Safe fix:
+
+- inspect the reported speaker and filesystem error, repair the prepared input
+  or canonical-output path when needed, then retry transcribe normally;
+- allow a legacy aggregate-only record to regenerate once; and
+- do not edit the manifest or copy an old JSON file into place as a substitute
+  for a successful checkpoint.
+
+```bash
+narratio run-stage transcribe 2026-04-04
+```
+
+Valid earlier speaker checkpoints remain reusable even while aggregate
+transcribe status is failed or interrupted. Merge remains gated until
+transcribe reaches aggregate success with the complete current set.
+
+Relevant reference: [Operations: Transcription continuation and replacement](./operations.md#transcription-continuation-and-replacement).
+
+## WhisperX model changed but transcription was reused
+
+Symptom:
+
+- WhisperX model weights, prompts, or private server configuration changed at
+  the same configured URL, but Narratio still considers speaker transcripts
+  current.
+
+Likely cause:
+
+- Narratio can fingerprint its configured URL and language, not private state
+  loaded behind the service boundary.
+
+Safe fix:
+
+- explicitly force transcribe to establish a durable reset, then use ordinary
+  retry if the replacement attempt is interrupted.
+
+```bash
+narratio run-stage transcribe 2026-04-04 --force
+```
+
+Transport replay and application retries do not provide an exactly-once remote
+execution guarantee. Investigate server-side failures or duplicate work using
+WhisperX diagnostics; do not infer completion from a server log without the
+local speaker checkpoint.
+
+Relevant references: [WhisperX integration](./integrations/whisperx.md) and
+[Transcribe internals](./internal/stage-transcribe.md).
+
+## Transcription manifest checkpoint failed
+
+Symptom:
+
+- transcribe reports that a speaker completed but the session manifest could
+  not be saved.
+
+Likely causes:
+
+- the workspace is unwritable or out of space;
+- the manifest path or parent directory is unsafe or the wrong type; or
+- a transient filesystem error interrupted atomic replacement.
+
+Safe fix:
+
+- correct the reported filesystem or permission problem and retry transcribe
+  normally. Narratio reconciles from the last readable collection and reuses
+  only successfully checkpointed speakers.
+
+A canonical raw transcript left by the failed checkpoint is incidental and
+does not become reusable authority. Preserve the manifest and diagnostics if
+the failure repeats; do not advertise the file by editing manifest evidence.
+
+Relevant references: [Manifest persistence](./internal/manifest.md#persistence-semantics)
+and [Transcribe internals](./internal/stage-transcribe.md).
+
 ## Notarius credential reference unavailable
 
 Symptom:
@@ -580,18 +674,22 @@ Symptom:
   or unsupported; or
 - restore rejects a committed remote session manifest for the same reason.
 
-Likely cause:
+Likely causes:
 
 - the manifest predates the supported canonical state contract. Narratio
   rejects it at the schema boundary rather than interpreting aggregate output
-  lists or incidental files as current authority.
+  lists or incidental files as current authority; or
+- an older strict-decoding Narratio binary is reading a current manifest that
+  contains additive transcribe speaker state it does not recognize.
 
 Safe fix:
 
 - for unsupported local state, move the old manifest aside and regenerate, or
   restore a verified current committed snapshot when one is authoritative;
 - for unsupported committed remote state, regenerate healthy local state as
-  needed and republish the session.
+  needed and republish the session; and
+- for a downgrade rejection, return to the current binary or restore a verified
+  pre-upgrade backup. Do not delete only the speaker fields by hand.
 
 ```bash
 narratio run 2026-04-04
@@ -603,7 +701,7 @@ old files into canonical paths merely to influence selection; availability is
 manifest-owned.
 
 Relevant references: [Operations: Stage Execution and Continuation Behavior](./operations.md#stage-execution-and-continuation-behavior)
-and [Manifest Internals](./internal/manifest.md#analyze-owned-artifact-state).
+and [Manifest Internals](./internal/manifest.md#transcribe-owned-speaker-state).
 
 ## Scriptorium private input changed without a rerun