Document accepted chunk map export

docs/internal/modules.md

@@ -391,6 +391,12 @@ safe logical names, pretty-prints JSON payloads, and assembles the logical index
 manifest, rejected-result, warning, and lane files. Invalid JSON, unsupported
 media types, unsafe names, and sanitized-name collisions are errors.
 
+Its strict `include_chunk_map` option is disabled by default. When enabled, it
+validates the framework-supplied accepted chunk map through its codec and adds
+the pipeline-wide `chunk-map.json` plus its index descriptor; it does not treat
+the map as a lane payload. The external shape is owned by the
+[Accepted Chunk Map contract](../integrations/chunk-map.md).
+
 The encoder returns logical files only. The CLI places them on disk, and the
 [JSON output contract](../integrations/json-output.md) defines their external
 paths and schemas.