[afpruivo]

Coucou for Windows can crash with heap corruption (0xC0000374, no panic, no log line: the process just disappears) when many hook connections open and close quickly on the relay pipe. The cause is in mio 1.2.3, the library under tokio's named pipes: a use-after-free reported as tokio-rs/mio#2011 and fixed by tokio-rs/mio#2014 in mio 1.2.4.

This PR only bumps mio 1.2.3 → 1.2.4 in windows/Cargo.lock (two lines; nothing else in the lockfile changes, cargo test --locked accepts it).

How I found it. While testing #872 (#853, hook server stops after a failed connect), I hammered the pipe: 8 workers opening and closing client connections for 10 s (script below). Coucou didn't hang; it crashed. Windows' crash log shows coucou.exe with c0000374 each time.

Verification on Windows 11 Pro 26H2 (20-thread CPU):

Build	mio	Result
Installed 0.5.2	1.2.3	crashed
#872 branch	1.2.3	crashed 3/3
Minimal tokio-only copy of pipe.rs's loop (no Coucou code)	1.2.3	crashed 6/6
Same minimal copy	1.2.4	survived 6/6
This branch	1.2.4	survived 3/3, real Claude Code hooks still arrive afterwards

The minimal copy crashes even when each connection is dropped right away without reading, so it's not Coucou's handler code.

cargo test --lib: 516 passed. npm test: 466 passed.

Does it happen in normal use? I haven't seen it happen on its own: a normal session sends far fewer connections than this test. The mio issue says it needs a busy multi-threaded runtime, which a burst of parallel subagents or a loaded machine can produce. So it's a rare crash, but an easy fix.

About #872: in these runs, the failed-connect() path it fixes never ran, so this doesn't replace it. It just fixes a different way the relay pipe can die.

Stress script (PowerShell)

$name = "coucou-" + [System.Security.Principal.WindowsIdentity]::GetCurrent().User.Value
$jobs = 1..8 | ForEach-Object { Start-Job -ArgumentList $name { param($name)
  $end = (Get-Date).AddSeconds(10)
  while ((Get-Date) -lt $end) {
    $c = New-Object System.IO.Pipes.NamedPipeClientStream(".", $name, [System.IO.Pipes.PipeDirection]::InOut)
    try { $c.Connect(50) } catch {} finally { $c.Dispose() }
  } } }
$jobs | Wait-Job | Out-Null
Get-Process coucou   # gone on mio 1.2.3

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