The buffer truncation code was slicing at a raw byte offset which could
land in the middle of a multi-byte character (like emojis), causing a
panic. Fixed by using char_indices() to find valid character boundaries.
Also added stop_reason field to CompletionChunk initializers in tests
to complete the stop_reason feature addition.
- Fix byte boundary panic in filter_json.rs line 327
- Add test for multi-byte character handling
- Update test files with missing stop_reason field
Added 13 tests to verify that duplicate detection only catches
IMMEDIATELY SEQUENTIAL duplicates:
- test_find_complete_json_object_end_* - Tests for JSON parsing helper
- test_same_tool_with_text_between_not_duplicate - Key test ensuring
tool calls separated by text are NOT duplicates
- test_different_tools_back_to_back_not_duplicate
- test_same_tool_different_args_not_duplicate
- test_identical_tool_calls_back_to_back_are_duplicates
- test_has_text_after_tool_call - Tests text detection logic
- test_tool_call_with_newlines_between
- test_tool_call_with_whitespace_text_between
- test_tool_call_in_middle_of_text
- test_multiple_different_tool_calls_with_text
Also made find_complete_json_object_end public for testing.
