Register D&D scene chunker

docs/troubleshooting.md

@@ -177,6 +177,31 @@ Fix:
 
 Provider error messages are redacted for configured API key values.
 
+## Scene Chunking Failure
+
+Symptoms include:
+
+- `dnd scenes chunker`
+- `malformed structured output`
+- `start_unit_id`
+- `end_unit_id`
+- `gap`
+- `overlap`
+- `final scene`
+- `complete structured output`
+
+Fix:
+
+- Validate the pipeline configuration and confirm the input module provides a
+  transcript source when using `chunk: dnd/scenes`.
+- Confirm the LLM profile has a working OpenAI-compatible `base_url`, `model`,
+  and credentials.
+- Inspect retained diagnostics for the run error and resolved pipeline.
+- If the error names malformed structured output, retry with a model that
+  follows structured response schemas reliably.
+- Scene boundaries must use exact source-unit IDs, cover the full source
+  document, be contiguous, and not overlap.
+
 ## Output Write Failure
 
 Symptoms include: