feat: persist supervised process PID evidence

internal/client/supervisor/supervisor.go

@@ -130,6 +130,9 @@ func windowsExecutionContext(value string) (rvboxv1.WindowsExecutionContext, boo
 type Process interface {
 	IssueUUID() domain.UUID
 	Identity() EffectiveIdentity
+	// PID is immutable process evidence used only for diagnostics/recovery
+	// correlation; callers must never signal a process by PID alone.
+	PID() uint32
 	// Release crosses the durable launch-authorized barrier. A native Windows
 	// process is created suspended and must not execute before this call.
 	Release(context.Context) error

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)
 	}