test(agentcompat): add process supervision harness

Co-authored-by: naiba/CloudCode <hi+cloudcode@nai.ba>

integration/agentcompat/internal/workspace/residue_test.go

@@ -0,0 +1,72 @@
+//go:build linux
+
+package workspace
+
+import (
+	"context"
+	"errors"
+	"io"
+	"os"
+	"os/exec"
+	"strings"
+	"syscall"
+	"testing"
+)
+
+func TestWorkspace_PreservesEvidenceWhenProcessGroupRemains(t *testing.T) {
+	// Given
+	workspace, err := New(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	root := workspace.Root()
+	command, input := startWorkspaceHelper(t)
+	if err := workspace.TrackProcessGroup(command.Process.Pid); err != nil {
+		t.Fatal(err)
+	}
+
+	// When
+	err = workspace.Close()
+
+	// Then
+	if err == nil || !strings.Contains(err.Error(), "process group") {
+		t.Fatalf("close error = %v", err)
+	}
+	if _, statErr := os.Stat(root); statErr != nil {
+		t.Fatalf("workspace evidence was removed: %v", statErr)
+	}
+	if err := input.Close(); err != nil {
+		t.Fatal(err)
+	}
+	if err := command.Wait(); err != nil {
+		t.Fatal(err)
+	}
+	if err := workspace.Close(); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := os.Stat(root); !errors.Is(err, os.ErrNotExist) {
+		t.Fatalf("workspace remains after group exit: %v", err)
+	}
+}
+
+func TestWorkspaceHelper(t *testing.T) {
+	if os.Getenv("GO_WANT_WORKSPACE_HELPER") != "1" {
+		return
+	}
+	_, _ = io.Copy(io.Discard, os.Stdin)
+}
+
+func startWorkspaceHelper(t *testing.T) (*exec.Cmd, io.WriteCloser) {
+	t.Helper()
+	command := exec.Command(os.Args[0], "-test.run=^TestWorkspaceHelper$")
+	command.Env = append(os.Environ(), "GO_WANT_WORKSPACE_HELPER=1")
+	command.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
+	input, err := command.StdinPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := command.Start(); err != nil {
+		t.Fatal(err)
+	}
+	return command, input
+}