cmux Debugging

Debug event log

Put debug event instrumentation (keys, mouse, focus, splits, tabs) in the unified DEBUG build log. This is not a requirement to log every new code path; most probes belong to a dogfood debug loop and are removed before merge.

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

• Untagged Debug app logs to /tmp/cmux-debug.log; tagged (./scripts/reload.sh --tag <tag>) to /tmp/cmux-debug-<tag>.log.
• reload.sh writes the current log path to /tmp/cmux-last-debug-log-path and the selected dev CLI path to /tmp/cmux-last-cli-path, and points /tmp/cmux-cli and $HOME/.local/bin/cmux-dev at that CLI.
• Implementation: Packages/macOS/CMUXDebugLog/Sources/CMUXDebugLog/DebugEventLog.swift. App shim: Sources/App/DebugLogging.swift. Both are #if DEBUG, so every call site must be wrapped in #if DEBUG / #endif.
• cmuxDebugLog("message") timestamps and appends in real time. A 500-entry ring buffer backs it; CMUXDebugLog.DebugEventLog.shared.dump() writes the full buffer to file.
• Key events are logged in AppDelegate.swift (monitor, performKeyEquivalent); mouse/UI events inline in views (ContentView, BrowserPanelView).
• Stable event prefixes: focus.panel, focus.bonsplit, focus.firstResponder, focus.moveFocus, tab.select, tab.close, tab.dragStart, tab.drop, pane.focus, pane.drop, divider.dragStart.

Profiling

Profile a tagged build by attaching to its pid (xctrace record --attach <pid>, sample <pid>). Never use xctrace --launch or Instruments' launch mode on any cmux bundle, and never quit, kill or relaunch the user's running cmux (com.cmuxterm.app): it holds their live agent sessions, and on 2026-09-26 a suspected profiler relaunch took five of them down.

Debug menu

DEBUG builds get a Debug menu in the macOS menu bar. When the user says "debug menu" or "debug window" they mean this, not defaults write.