feat: port upstream changes from pi-mono (72047c05..55769e75)
AI provider fixes:
- Fixed Claude tool prefix matching and Gemini 3 unsigned tool handling
- Added Bedrock thinking budget guardrails and tool id sanitization
- Added tool argument coercion and Codex response retry logic
TUI improvements:
- Improved Kitty key handling and editor behavior (scrolling, padding, kill ring)
Coding agent changes:
- Added extension input interception, compaction helpers, and UI updates
- Added session forking prompt for cross-project sessions
- Added APPEND_SYSTEM discovery, piped stdin print mode, and key hint exports
Docs:
- Updated pi-mono sync point
can1357
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