feat: persist supervised process PID evidence

internal/client/supervisor/windows/native_exec.go

@@ -116,6 +116,13 @@ func (process *execProcess) IssueUUID() domain.UUID { return process.issue }
 
 func (process *execProcess) Identity() supervisor.EffectiveIdentity { return process.identity }
 
+func (process *execProcess) PID() uint32 {
+	if process == nil {
+		return 0
+	}
+	return process.pid
+}
+
 // Release is the second half of the durable launch barrier. The portable
 // adapter has no suspended native handle, so its release is intentionally a
 // no-op; the Windows adapter supplies a ResumeThread closure.

internal/client/supervisor/windows/native_other_test.go

@@ -48,6 +48,9 @@ func TestPortableSupervisorCapturesOutputAndSupportsStdin_HP_SUPERVISOR_03(t *te
 	if err != nil {
 		t.Fatal(err)
 	}
+	if process.PID() == 0 {
+		t.Fatal("portable supervisor did not expose process identity PID")
+	}
 	if err := process.WriteStdin(context.Background(), []byte("hello"), true); err != nil {
 		t.Fatal(err)
 	}