Stale sessions keep running an old (deleted) binary after an in-CLI update, and idle sessions never trim their heap (~460 MB held for hours)

[turgs]

Describe the bug

Running the CLI in multiple terminal tabs and updating from one of them leaves
the others silently running the old version against a now-deleted binary, and
those abandoned/idle sessions never trim memory — one sat at ~460 MB / 23
threads for hours while doing nothing.

How it actually happens (common workflow)

1. Two (or more) CLI sessions are open, one per terminal tab.
2. In tab A I run the in-CLI update command (e.g. /update). It replaces the
   binary on disk and tab A restarts on the new version.
3. Tab B keeps running the old version. On Unix, replacing/unlinking an
   in-use executable is allowed, so tab B's process keeps the old inode
   mapped — readlink /proc/<pid>/exe shows .../copilot-cli/1.0.11/copilot **(deleted)**. Nothing tells tab B it is now outdated.
4. Later I forget tab B is even there. It sits idle but still resident at
   ~460 MB, contributing to swap pressure on a 16 GB machine.

This is not a one-off — with several tabs open it happens on nearly every update.

What this is NOT

To be precise, this is not a runaway-CPU bug. top/ps showed the idle
session at ~45% CPU, but that is the lifetime average (utime+stime ÷ elapsed), inflated by work done earlier while the session was active. Direct
sampling of /proc/<pid>/stat over 10 s showed 0% CPU at idle, with only
occasional ~1-core-second bursts minutes apart. A disarmed timerfd, 3 inotify
watches, and libuv-internal socketpairs (no network peers) all confirm there is
no busy loop. The reportable problems are (a) no stale-version signal after an
update and (b) no idle memory trim — not CPU.

Affected version

copilot 1.0.72 (current), with a lingering 1.0.11 session in another tab.

Steps to reproduce the behavior

1. Open the CLI in two terminal tabs.
2. Run the in-CLI update from tab A (or brew upgrade the cask) so the on-disk
   binary is replaced.
3. Leave tab B open and idle.
4. Inspect tab B's process (Linux):
   • readlink /proc/<pid>/exe -> .../1.0.11/copilot (deleted)
   • grep VmRSS /proc/<pid>/status -> ~460 MB still resident
   • awk '{print $14+$15}' /proc/<pid>/stat sampled over 10 s -> ~0 at idle
     (confirming the "high CPU" in top is a lifetime average, not current).

What might be nicer (just ideas)

• After an update, it'd be handy if a still-running older session could somehow
  notice it's outdated and gently suggest restarting it — right now nothing
  hints that the tab is stale.
• And it'd be nice if a long-idle session didn't sit at hundreds of MB forever,
  though I appreciate that's easier said than done.

Some notes on the idle-memory side

Caveat up front: I'm not familiar with the CLI internals, so this is hand-wavey
and quite possibly misses context you already have. Just sharing what I bumped
into in case it's useful.

From what I understand, for a V8-based runtime GC on its own doesn't tend to hand
memory back to the OS — V8 holds freed pages for reuse, and on Linux glibc keeps
freed memory in per-arena free lists. So if trimming an idle session were ever
worth doing, my rough mental model is that it might involve something like:

• noticing the session has been idle for a while,
• a full GC (global.gc() / --expose-gc) to clear dead objects — though on its
  own that often doesn't move RSS much,
• something like V8's Isolate::LowMemoryNotification(), which seems more likely
  to actually release pages (not a userland-JS thing, but the CLI is the embedder
  so presumably it could), and
• on Linux, maybe a malloc_trim(0) / MALLOC_ARENA_MAX type step, since glibc
  otherwise seems to sit on the freed arenas.

Very possibly there are good reasons not to bother — a high-but-stable RSS is
normal for V8 and isn't itself a leak, and forcing GC has trade-offs. Mostly
flagging the ~460 MB idle footprint; the how is your call.

Is this Linux-only?

Not sure, but a rough guess:

• The "GC doesn't lower RSS" bit seems like it'd be all-platform (V8 behavior).
• The "old session keeps running as a deleted binary" bit feels Unix-y —
  Linux/macOS happily let you replace an in-use executable, whereas on Windows a
  running .exe is usually locked, so an in-place update probably fails or
  defers differently. Either way the stale tab presumably still runs the old code.
• Any allocator-arena step (malloc_trim, etc.) would be glibc/Linux-specific;
  macOS/Windows use different allocators.

So if anything here is worth acting on, the stale-version heads-up feels like
the cross-platform, lower-risk half; the idle-memory trimming is fuzzier and more
platform-dependent. But you'd know far better than me.

Additional context

• OS: Linux (x86_64), 4 cores / 16 GB, bash, gnome-terminal
• Install: Homebrew cask copilot-cli
• Evidence gathered via /proc/<pid>/{stat,status,fd,fdinfo} (strace blocked by
  ptrace_scope). Full sampling transcript available on request.