fix: prevent parser poisoning from inline tool-call JSON patterns

The streaming parser was incorrectly detecting tool call patterns that
appeared inline in prose (e.g., when explaining the format), causing
g3 to return control mid-task.

Fix: Modified find_first_tool_call_start() and find_last_tool_call_start()
to only recognize patterns that appear on their own line (at start of
buffer or after newline with only whitespace before the pattern).

Changes:
- Added is_on_own_line() helper to check line-boundary conditions
- Updated detection methods to skip inline patterns
- Removed sanitize_inline_tool_patterns() and LBRACE_HOMOGLYPH (no longer needed)
- Rewrote tests for new behavior
- Added streaming_repro tests that use process_chunk() to verify the exact bug scenario

28 tests covering: streaming repro, line boundaries, Unicode, code contexts, edge cases

crates/g3-core/src/lib.rs

@@ -93,7 +93,7 @@ pub enum StreamState {
 }
 
 // Re-export StreamingToolParser from its own module
-pub use streaming_parser::{sanitize_inline_tool_patterns, StreamingToolParser, LBRACE_HOMOGLYPH};
+pub use streaming_parser::StreamingToolParser;
 
 pub struct Agent<W: UiWriter> {
     providers: ProviderRegistry,