Update D&D schemas to require integer unit_id values

docs/internal/modules.md

@@ -125,10 +125,13 @@ Provides:
 Options: none. Non-empty options are rejected.
 
 The chunker enforces full source-unit coverage from the first source unit to the
-last, exact source-unit IDs, sequential contiguous scenes, and no overlap. It
-assigns chunk IDs such as `scene-000001` and stores scene metadata including
-title, primary mode, participants, summary, boundary note, confidence, boundary
-unit IDs, and unit count. Boundary caveats become warnings with reason code
+last, sequential contiguous scenes, and no overlap. Its LLM-facing schema uses
+integer `start_unit_id` and `end_unit_id` values as 1-based source-unit numbers;
+the module canonicalizes valid integer references to source-unit IDs before
+producing chunks. It assigns chunk IDs such as `scene-000001` and stores scene
+metadata including title, primary mode, participants, summary, boundary note,
+confidence, boundary unit IDs, and unit count. Boundary caveats become warnings
+with reason code
 `scene_boundary_caveat`. Whitespace-only caveats are treated as malformed
 structured output rather than silently dropped.
 
@@ -146,6 +149,9 @@ the embedded Scriptorium prompt ID, prompt version, transcript and reference
 input materials, response schema, and session ID to the runtime; converts
 spell-cast responses into artifact candidates; and supplies deterministic
 validators.
+Its LLM-facing source-reference schema uses integer `start_unit_id` and
+`end_unit_id` values as 1-based source-unit numbers; the module canonicalizes
+valid integer references to source-unit IDs before validation and output.
 
 Its prompt definition lives under `assets/prompts` and its schema under
 `assets/schemas`. Shared reusable D&D prompt fragments are provided by

docs/troubleshooting.md

@@ -263,7 +263,7 @@ Fix:
   follows structured response schemas reliably.
 - If the error names `boundary_caveats`, check for blank or whitespace-only
   caveat text in the scene response.
-- Scene boundaries must use exact source-unit IDs, cover the full source
+- Scene boundaries must resolve to valid source units, cover the full source
   document, be contiguous, and not overlap.
 
 ## Session ID