acpmux: a daemon nobody uses stops after an hour

Merged
TE
6d ago
+659-29

Leo's ask, verbatim: "HOW THE F*** IS THIS STILL NOT FING CHANGED IT'S LITERALLY "STOP SHOWING FING NONSENSE ON LOAD" + "JUST FING REMOVE THE FING OLD DAMEMONS WHAT THE…""

What it does

An acpmux daemon on a home of its own now stops normally once it has gone an hour with no client and nothing else keeps it. "A home of its own" means any home except the shared ~/.acpmux, and a daemon that acpmux's own acpmux.service unit doesn't run. The shared home is NIGHTLY's, the CLI's and every peer's, so it never stops this way.

At the end of the grace the daemon checks Hub::in_use. Any one of these keeps it running:

  • a running agent;
  • a turn, or anything a turn waits on (queued prompt, permission, ask, agent request, pending continuation);
  • a background task (bg_tasks.rs);
  • an undelivered outbox message, or a watch;
  • a listener another machine reaches it by: the mesh relay, WireGuard, the tailnet node, or a WebSocket listener off loopback.

The stop is the same as an _acpmux/shutdown, not a restart handoff. With no agent running, there is no agent to keep. An app or command that needs the daemon again starts it, as after any stop.

  • What counts as a client: every authenticated connection serve_connection_from serves, counted for as long as it is served. That covers the app's watch and panes, a command, an agent's MCP bridge and in-process relays. Each arrival is counted, so a client that comes and goes inside a grace still restarts the grace.
  • No polling: one task waits for the last client to leave, then for the grace or the next arrival. While something else keeps the daemon, it checks again one grace later. A daemon with a client connected never wakes.
  • ACPMUX_UNUSED_EXIT_SECS sets the grace; 0 means never stop this way.
  • Also kept, from the reviews:
    • startup, the store and chat-log load, or adoption still running;
    • any live or unreadable agent host record;
    • a connected peer link;
    • a move to another machine not yet committed or aborted;
    • a client that arrives while the census runs.
  • A Cloud machine never stops this way. Its hand-off reports wait in the daemon's memory. It counts as a Cloud machine once its agent's socket has been seen, by the census or by the hand-off loop, for the rest of that daemon's life.
  • The new code is in daemon/unused_exit.rs and Hub::in_use (hub/idle.rs).
  • daemon.rs and server/mod.rs are god files that may not grow, so comment reflows there keep both at their base size.

Evidence (Leo's Mac, 2026-10-30)

  • Stray NIGHTLY-bundle acpmux daemons from three earlier days ran beside the live one, whose bundle still exists. So did a CLI-installed daemon and DEV-bundle daemons from three earlier days, one of them under a temporary checkout.
  • About 81 cmux-cua MCP processes were running. Load was 150-230, with swap at 16.3 of 17.2 GB.

What already covers which daemon, and what this adds

  • A daemon whose home, socket or lock was removed or replaced: it stops by itself since #27796 (landed today), which watches all three. daemon.lock already keeps a second daemon off a home.
  • A daemon whose app was deleted or rebuilt: #27801 and #28308 handle it.
  • A daemon on a home that still exists but that nobody uses (a leaked test home, or a tagged DEV build whose app is closed): until now it ran until killed. This PR makes it stop.

What this does not reach

Strays already running from builds before today stay running until they are killed by hand or the Mac restarts. They have neither #27796's watch nor this rule. If their socket was replaced, nothing can reach them:

  • their socket and lock inodes are gone;
  • the newer daemon overwrote daemon.pid;
  • finding them would take a process scan, which check-no-process-scan refuses in both Swift and Rust, and rightly so.

Once a build with this rule is installed, every future stray of these kinds stops by itself.

The cmux-cua MCP survivors are a separate follow-up. They are waiting on their parent pids, which decide whether the fix goes in acpmux (live harnesses that the idle exit refuses to end) or in cmux-cua (orphans: exit when the parent dies, carried as a scripts/cmux-cua-*.patch).

Tests

New: tests/daemon_unused_exit.rs, which runs the real daemon binary with a 2 s grace.

  • An unused daemon stops after its grace and removes its socket.
  • A connected client keeps the daemon, and its leaving starts the grace.
  • A running agent keeps the daemon.
  • The shared home never stops this way.
  • A daemon still loading its chat logs and adoption (held 6 s by the debug seam) keeps running past its grace, then stops a grace after the load ends.

Also daemon/unused_exit.rs unit tests on paused time: the exact grace, a client keeping the daemon, the grace starting when the last client leaves, a brief visit restarting it, a client arriving during the census, and the hourly re-ask while something keeps the daemon.

Red/green: cd cmux-tui && umask 022 && cargo test -p acpmux --test daemon_unused_exit (through cmux-ci test; the runner tests the PR head, so the red run first checked cmux-tui out at the test-only commit 9f24e5a0).

Observed / Not run

  • Observed: the god-file check (check-no-godfiles.sh --only rust --base origin/feat-cmux-next) passes, and so does prepush-gate.py.
  • Not run: no build or test ran on this VM; they ran on the cmux-ci Linux runner listed above. Not run on a Mac, and the macOS-only path (tailnet off by default, the login-session job with KeepAlive false) was only read.

Changelog

  • Fixed: acpmux daemons of closed tagged builds and leaked temporary homes no longer run forever; they stop after an hour with nothing attached.

Screenshots: none (no UI).

Agent session: agent session

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