Tools now go through permission.Checker before executing:
- plan mode: denies all writes (fs.write, bash), allows reads
- bypass mode: allows all (deny rules still enforced)
- default mode: prompts user (pipe: stdin prompt, TUI: auto-approve for now)
- accept_edits: auto-allows file ops, prompts for bash
- deny mode: denies all without allow rules
CLI flags: --permission <mode>, --incognito
Pipe mode: console Y/N prompt on stderr
TUI mode: auto-approve (proper overlay TODO)
Verified: plan mode correctly blocks fs.write, model sees error.