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bug(pty): the main process leaks PTY masters until macOS runs out (509/511 after 13h) #1437
Description
Evidence (2026-09-27 14:30Z, packaged app, main pid 94543, uptime 13h26m)
lsof -p 94543 | awk '$NF=="/dev/ptmx"' | wc -l→ 509 open PTY masters.kern.tty.ptmx_max= 511.- Only 34 agents or terminals exist in the window (ac_agents_list), and only 68 processes system-wide have a tty.
- Result: new agents and terminals fail to spawn. Orchestration reviewers for fix(conversations): an unreadable conversation file is said, not 'no prompts' (#1306) #1434 and fix(extensions): the runtime harness no longer races a test-local 3 s startup deadline #1436 failed with a full PTY table (steering q117).
- The session closed about 60 reviewer agents and reloaded workers several times (
ac_agents_reload, bug(claude): a prompt whose absorption times out is left in the native composer, and every later delivery refuses it as a human draft #1350), so PTY masters of closed or replaced sessions are likely never closed.
Expected
Closing, reloading or replacing an agent or terminal closes its PTY master. The number of open ptmx fds tracks the number of live sessions.
Next
Find which close or replace path skips pty.kill() / fd close (node-pty). Pin it with a test that counts open ptmx fds before and after N create/close/reload cycles.
Workaround: restart the app (it frees all masters).
🤖 Generated with Claude Code
Activity
Juliusolsson05 commentedon Sep 27, 2026
Root cause found; fix in #1439.
node-pty 1.1.0 (our pinned version, still npm
latest) leaks one/dev/ptmxper spawn on macOS. Insrc/unix/pty.ccpty_posix_spawn, thelow_fdsloop opens a ptmx and breaks atcount == 0whenever stdio is open (always, in Electron). The cleanup,for (; count > 0; count--) close(low_fds[count]), never closeslow_fds[0].It matches the live evidence (main pid 94543): 506
/dev/ptmxfds, but only 16 slave fds, and those are exactly the 16 ttys with a live process. The orphans have no slave and no process, which is thelow_fds[0]signature. It is not a session-lifecycle bug in our close or reload paths: every spawn leaks, whatever happens to the session afterwards.Upstream: microsoft/node-pty#882 ("fix: /dev/ptmx leak on macOS", for microsoft/vscode#182212). It shipped only in 1.2.0-beta.10 and later.
#1439 ports #882 as a sha256-guarded source patch in postinstall, before electron-rebuild, and pins node-pty to 1.1.0. Until a build with it ships, every spawn still leaks, and only an app restart frees the table.
🤖 Generated with Claude Code