feat(tools): add exec tool enhancement with background execution and PTY support (#1752)
- Unified exec tool with actions: run/list/poll/read/write/send-keys/kill
- PTY support using creack/pty library
- Process session management with background execution
- Process group kill for cleaning up child processes
- Session cleanup: 30-minute TTL for old sessions
- Output buffer: 100MB limit with truncation
Actions:
- run: execute command (sync or background)
- list: list all sessions
- poll: check session status
- read: read session output
- write: send input to session stdin
- send-keys: send special keys (up, down, ctrl-c, enter, etc.)
- kill: terminate session
Tests:
- PTY: allowed commands, write/read, poll, kill, process group kill
- Non-PTY: background execution, list, read, write, poll, kill, process group kill
- Session management: add/get/remove/list/cleanup
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