Verify at the write boundary

Implement write-time verification. On every file write or edit: run the appropriate fast check for the file type (python: compile/ruff; js/ts: esbuild parse or tsc; json/yaml: parse) within a second-scale budget; on failure, revert the write (or never apply it - validate a staged copy) and return the exact error with line numbers to the model as the tool result; on success, return a confirmation including the check that ran. Wire this into the edit tool itself so no write path skips it. Test with a deliberately broken edit and confirm the revert-and-teach cycle produces a corrected second attempt.