cmux Debugging

Debug event log

When adding debug event instrumentation, put events (keys, mouse, focus, splits, tabs) in the unified DEBUG build log. This is not a blanket requirement to add logs to every new code path. Most temporary probes should be added only during the dogfood debug loop and removed before merge.

tail -f "$(cat /tmp/cmux-last-debug-log-path 2>/dev/null || echo /tmp/cmux-debug.log)"