Debugging

This page is the practical “something’s off, where do I look first” reference. AgentMux’s three-process design means logs, state, and crash artifacts each live in a specific place — the trick is knowing which.

Logs at a glance

Source	File	Tail recipe
Host (CEF) — includes frontend `[fe]` console	`<data-dir>/logs/agentmux-host-v<v>.log.<date>`	`muxlog host` (or `muxlog host '[fe]'` for frontend only)
Sidecar (`agentmux-srv`)	`<data-dir>/logs/agentmuxsrv-v<v>.log.<date>`	`muxlog srv`
Launcher (early-startup)	`~/.agentmux/logs/agentmux-launcher.log`	`cat "$AGENTMUX_LOG_DIR/agentmux-launcher.log"`
Launcher reducer events	`<data-dir>/data/launcher-events.log`	`tail -F` directly (JSONL)

The launcher log is the only one outside the per-version data dir — it’s the early-startup file the launcher writes before paths are fully resolved.

Pointer files

Daily log rotation means the active filename changes at UTC midnight. Rather than guessing, every host + sidecar process writes a pointer file with the current absolute path:

LOG="$(cat ~/.agentmux/logs/current-host-v<version>.path)"
tail -F "$LOG"

The same convention applies for the sidecar (current-srv-v<version>.path). The pointer file is rewritten on each launch and on every rotation.

The shipped muxlog shell helper does this lookup for you and also handles the legacy basename-only pointer format used by older instances. See Multi-instance & dev mode for the full pointer story.

Frontend `[fe]` logs go to the host log, not DevTools

Every console.log/warn/error/debug/info call in the frontend is monkey-patched at startup by frontend/log/log-pipe.ts and forwarded to the host via the fe_log_structured CEF IPC command. They land in the host log, tagged [fe] with module=console:

INFO agentmux_lib::commands::backend: [fe] my message module=console

So:

Don’t tell users to open DevTools (F12) — the frontend logs aren’t there.
muxlog host '\[fe\]' filters the host log to frontend output only.
Live tail during repro: keep the dev terminal open with task dev; [fe] lines appear inline.

Reducer dispatch ring

Every slice in the reducer stack routes through command-source.ts’s recordDispatch(...) helper, which appends a structured record (slice name, key, command, emitted events, source, timestamp) to an in-memory ring buffer. The diagnostics panel surfaces this.

When a question like “what mutated this state?” comes up, filter the ring for the relevant key — the answer is one entry. This was the discriminator in the SolidJS reactive-leak storm crashes that earlier attempts (PRs #708, #721, #722) chased the wrong way.

WRR drift diagnostics

Window Reality Reconciliation reconciles AgentMux’s model against Win32 reality. When a window appears to “freeze” or windows mysteriously vanish, the launcher reducer’s event log is the authority. Useful greps:

grep -E "HiddenSinceOpen|HwndWithoutBrowser|WRR-DRIFT|wfr:gate|wfr:runner|pending=" \
    "$AGENTMUX_DATA_DIR/launcher-events.log"

HiddenSinceOpen and HwndWithoutBrowser indicate the window’s lifecycle state diverged from CEF’s view. WRR-DRIFT lines show the specific reconciliation action taken.

Sidecar crash dumps

The sidecar runs as a separate process auto-spawned by the host. If it crashes (e.g. a 0xC0000409 STACK_BUFFER_OVERRUN), the OS writes a minidump.

WER configuration is part of AgentMux’s installer; on a dev build, ensure the dump dir exists before reproducing. Open dumps in WinDbg (Windows) or lldb (macOS) / gdb (Linux) to inspect the crashing thread’s stack.

Chromium / renderer crashes

Renderer crashes come up as Crashpad reports. The host log captures the crash event; the dump itself lands in:

<data-dir>/cef-cache/Crashpad/reports/

For renderer-storm crashes (the screen flashes, panes blink, eventually CEF gives up): check the dispatch ring first, not the Crashpad stack. A reactive dependency leak in a shared utility produces the same symptoms as a real C++ crash but is diagnosed entirely from the ring. See PRs #708 / #721 / #722 for the specific recordDispatch pattern that caused it; instrument effect-run count before you fan out into hosts.

Shell-integration env block

Terminals opened inside AgentMux get an AGENTMUX_* env block. The muxlog helper, custom prompts, and pane-title color all rely on these:

echo "$AGENTMUX_BLOCKID"      # which block this terminal is in
echo "$AGENTMUX_LOG_DIR"      # where to look for host/srv logs
echo "$AGENTMUX_VERSION"      # which version this terminal was launched against
echo "$AGENTMUX_AGENT_ID"     # agent identity, if an agent owns the pane

If a terminal is missing these, the shell-integration scripts at ~/.agentmux/shell/ weren’t sourced — usually because the user opened the terminal outside AgentMux’s spawn path.

Useful greps cheat sheet

# Frontend only
muxlog host '\[fe\]'

# DnD / drag / tab-drop
grep -i "dnd\|drag\|tab-drag\|tab drop\|ReorderTab\|tab-reorder" "$LOG"

# Memory heartbeat (FileStore cache size, etc.)
muxlog host mem_heartbeat

# WRR drift
grep -E "HiddenSinceOpen|HwndWithoutBrowser|WRR-DRIFT|wfr:gate|wfr:runner" \
    "$AGENTMUX_DATA_DIR/launcher-events.log"

# Saga lifecycle
grep -E "saga.start|saga.step|saga.complete|saga.fail" "$LOG"

# Persist subscriber lag
grep -E "persist|broadcast|Lagged" "$LOG"

When to escalate

If three checks haven’t revealed the cause, stop investigating in isolation. The reducer dispatch ring, the launcher event log, and the host/sidecar logs collectively cover every cross-process state mutation. If the answer isn’t in those three sources, the question is probably wrong — file a bug with what you’ve ruled out.