fix: Suppress non-PMG error from Critical UI Error (#311)

* fix: Suppress non-PMG error from Critical UI Error

* fix: Code review fixes

---------

Co-authored-by: Sahil Bansal <bansalsahil315@gmail.com>

internal/proc/signal_unix.go

@@ -0,0 +1,19 @@
+//go:build !windows
+
+// Package proc decodes process termination status. It is a leaf utility shared
+// by the execution layer (runner) and the PTY session, so neither has to
+// reach through wrapper layers to learn how a child process ended.
+package proc
+
+import "syscall"
+
+// SignalInfo reports whether a process was terminated by a signal, given the
+// platform-specific status from (*exec.ExitError).Sys() / (*ptyx.ExitError).Sys().
+// signum is the signal number; callers form the conventional exit code as 128+signum.
+func SignalInfo(sys any) (signum int, signaled bool) {
+	ws, ok := sys.(syscall.WaitStatus)
+	if !ok || !ws.Signaled() {
+		return 0, false
+	}
+	return int(ws.Signal()), true
+}