fix(installers/windows): launcher captures daemon crash output

Signed-off-by: c2ndev <cannarella.dev@gmail.com>

Author: c2ndev

installers/windows/prempti-launcher.ps1

@@ -5,9 +5,11 @@
 
 .DESCRIPTION
     Hides the console window (via the PowerShell host invocation) and
-    invokes `premptictl daemon`. The supervisor owns the
-    Falco process, log files, rotation, and Claude Code hook lifecycle.
-    Runs in the foreground so the supervisor's stop signals reach it.
+    invokes `premptictl daemon`. The supervisor owns the Falco process,
+    log files, rotation, and Claude Code hook lifecycle. Runs in the
+    foreground so the supervisor's stop signals reach it. Captures the
+    supervisor's own stderr to log/supervisor.err so an early crash
+    (before Falco's logs are open) leaves a breadcrumb for the user.
 #>
 param(
     [string]$Prefix = (Join-Path $env:LOCALAPPDATA 'prempti')
@@ -17,5 +19,41 @@ Set-StrictMode -Version Latest
 $ErrorActionPreference = 'Continue'
 
 $Ctl = Join-Path $Prefix 'bin\premptictl.exe'
-& $Ctl daemon --prefix $Prefix
-exit $LASTEXITCODE
+$LogDir = Join-Path $Prefix 'log'
+if (-not (Test-Path $LogDir)) {
+    New-Item -ItemType Directory -Force -Path $LogDir | Out-Null
+}
+$SupervisorErr = Join-Path $LogDir 'supervisor.err'
+
+# Truncate per-run; only the latest launch's supervisor stderr is useful for
+# diagnosing a failed startup. Use UTF-8 without BOM so Add-Content / external
+# tools don't have to skip a BOM.
+[IO.File]::WriteAllText($SupervisorErr, '', [System.Text.UTF8Encoding]::new($false))
+
+$psi = New-Object System.Diagnostics.ProcessStartInfo
+$psi.FileName = $Ctl
+$psi.Arguments = "daemon --prefix `"$Prefix`""
+$psi.UseShellExecute = $false
+$psi.RedirectStandardError = $true
+$psi.CreateNoWindow = $true
+$proc = [System.Diagnostics.Process]::Start($psi)
+
+# Drain stderr asynchronously to avoid a 4 KB OS pipe-buffer deadlock if the
+# supervisor logs steadily. Each line is appended to supervisor.err.
+$drain = Register-ObjectEvent -InputObject $proc -EventName ErrorDataReceived -Action {
+    if ($EventArgs.Data) {
+        [IO.File]::AppendAllText($Event.MessageData, $EventArgs.Data + "`r`n",
+            [System.Text.UTF8Encoding]::new($false))
+    }
+} -MessageData $SupervisorErr
+$proc.BeginErrorReadLine()
+
+$proc.WaitForExit()
+# Per MSDN, calling WaitForExit() a second time after the first returns ensures
+# all async events fire before we tear down the registration.
+$proc.WaitForExit()
+
+if ($drain) {
+    Unregister-Event -SourceIdentifier $drain.Name -ErrorAction SilentlyContinue
+}
+exit $proc.ExitCode