PTY Exited event never fires when DuplicateHandle fails, costing a 10s stall per session at shutdown #91

Found during the v0.6.0 pre-release review. Low severity on its own, but it likely compounds #82.

The bug

PseudoTerminal.MonitorExitAsync (added in #63 to fix the handle race in #39) returns early on a failed DuplicateHandle — before Exited?.Invoke():

if (!DuplicateHandle(GetCurrentProcess(), _hProcess, GetCurrentProcess(),
        out IntPtr waitHandle, 0, false, DUPLICATE_SAME_ACCESS))
{
    Log($"DuplicateHandle failed: {Marshal.GetLastWin32Error()}");
    return;                     // <-- Exited never fires
}
try { ... }
finally { CloseHandle(waitHandle); }
Exited?.Invoke();

Every other path fires it exactly once. This one silently doesn't.

Why it matters

MainWindow.DisposeAndWaitForExitAsync subscribes to Exited and waits on a TaskCompletionSource:

await Task.WhenAny(tcs.Task, Task.Delay(timeoutMs));   // timeoutMs: 10000

If Exited never fires, that session waits out its full 10-second timeout. The disposal loop is sequential, so with N affected sessions it's N × 10s added to shutdown.

Bounded rather than hanging, and DuplicateHandle on a process handle you already own effectively never fails — which is why this is low severity rather than urgent.

Fix

Move the invoke into a finally so every path fires it exactly once:

try
{
    if (!DuplicateHandle(...)) { Log(...); return; }
    try
    {
        await Task.Run(() => WaitForSingleObject(waitHandle, 0xFFFFFFFF));
        if (GetExitCodeProcess(waitHandle, out uint code)) ExitCode = unchecked((int)code);
    }
    finally { CloseHandle(waitHandle); }
}
finally { Exited?.Invoke(); }

Worth a unit test via the IPseudoTerminal seam asserting Exited fires on the failure path too.

Relationship to #82

#82 is about startup/shutdown scaling badly with live session count, attributed mostly to fixed sleeps. This is a second, independent contributor to the same symptom — a conditional 10s per session rather than a fixed delay. Worth ruling in or out while working #82, since with 40 sessions the two are hard to tell apart from the outside.