- Add get_screen_snapshot() method that doesn't mutate terminal state
- Use change counter for reliable activity detection instead of dirty flag
- Update screenshot handler to use non-mutating snapshot method
- Refactor tests to use shared fixtures and reduce duplication
- Update copilot-instructions.md with detailed Makefile usage
Add isTerminalReady() check before calling fitAddon.proposeDimensions()
in the initial fit loop to prevent 'viewport.scrollBarWidth' TypeError
when terminal is not fully initialized.