Rewrite JSON tool call filter with clean state machine
Fixes bug where JSON tool calls were printed as text due to chunking issues.
Changes:
- Complete rewrite of filter_json.rs with 3-state machine:
- Streaming: normal pass-through, watches for newline + whitespace + {
- Buffering: confirms/denies tool pattern with ~20 char buffer
- Suppressing: string-aware brace counting until balanced
- Character-by-character processing eliminates chunk boundary issues
- Proper handling of } inside JSON strings (was causing premature exit)
- Detects truncated JSON followed by complete JSON (LLM retry case)
- Removed regex dependency, simpler pattern matching
- Added 59 stress tests covering malformed JSON, partial patterns,
streaming edge cases, adversarial inputs, and real-world patterns
All 86 filter_json tests pass.
d96d8c1d90