[BAG] Implement partial message extraction (extract messages --count) #30
Description
Summary
The robocodec extract messages --count command does not work for BAG format files.
Current Behavior
$ robocodec extract messages input.bag output.bag --count 10
Error: Partial message extraction (count < total) requires format-specific iteration. Use the convert command for full file copying.
Expected Behavior
Should extract the first N messages from the BAG file and write them to a new BAG file.
Use Case
- Create smaller test files from large bag files
- Extract a sample of messages for debugging
- Process large files in batches
MCAP Status
This feature works for MCAP files, only BAG format is affected.
Related
- Similar to fix(bag): use decode_headerless instead of decode_ros1 for BAG messages #27 (decode_headerless support)
- Part of BAG feature parity with MCAP