fix: handle SELinux Docker mounts and stale VM images

src/sbx/cli.py

@@ -380,6 +380,22 @@ def _start_existing_vm_if_needed(
         )
         print(f"sbx: If it still fails, run `sbx recreate {vm_id} --force`.", file=sys.stderr)
         return 1
+    current = vm_state.existing_vm_start_config(vm_id)
+    if current is not None:
+        config = current[1]
+        for key in ("kernel_path", "rootfs_path"):
+            value = config.get(key)
+            if value is not None and not Path(str(value)).expanduser().exists():
+                print(
+                    f"sbx: VM '{vm_id}' references missing boot artifact: {value}",
+                    file=sys.stderr,
+                )
+                print(
+                    "sbx: This VM was likely created from a temporary or removed image.",
+                    file=sys.stderr,
+                )
+                print(f"sbx: Run `sbx recreate {vm_id} --force`.", file=sys.stderr)
+                return 1
     command = ["sandbox", "start", vm_id, "--boot-timeout", f"{boot_timeout:g}"]
     completed = runtime.run_smolvm_capture(command)
     if completed is None:

src/sbx/image/build_debian.py

@@ -187,7 +187,7 @@ def _docker_run_kernel_builder(
             "run",
             "--rm",
             "-v",
-            f"{work_dir}:/work",
+            f"{work_dir}:/work:z",
             "-w",
             "/work",
             tag,

tests/test_build_debian_image.py

@@ -275,7 +275,9 @@ def fake_run(command: list[str], *, check: bool) -> None:
         runs.append(command)
         if command[:3] == ["docker", "run", "--rm"] and "bash" in command:
             assert check is True
-            work_dir = Path(command[command.index("-v") + 1].split(":", 1)[0])
+            volume = command[command.index("-v") + 1]
+            assert volume.endswith(":/work:z")
+            work_dir = Path(volume.split(":", 1)[0])
             assert (work_dir / "build.sh").is_file()
             assert (work_dir / "check-config.sh").is_file()
             assert "CONFIG_VETH=y" in (work_dir / "config.fragment").read_text()

tests/test_cli.py

@@ -1195,6 +1195,33 @@ def fake_run_capture(
     assert "sbx recreate vm1 --force" in capsys.readouterr().err
 
 
+def test_start_existing_vm_with_missing_kernel_suggests_recreate(
+    monkeypatch: pytest.MonkeyPatch,
+    capsys: pytest.CaptureFixture[str],
+) -> None:
+    missing_kernel = "/tmp/sbx-no-credentials-deleted/.smolvm/images/sbx/vmlinux.bin"
+    monkeypatch.setattr(
+        vm_state,
+        "existing_vm_start_config",
+        lambda vm_id: (
+            "stopped",
+            {"kernel_path": missing_kernel, "rootfs_path": "/tmp/not-checked.ext4"},
+        ),
+    )
+    monkeypatch.setattr(
+        cli.runtime,
+        "run_smolvm_capture",
+        lambda argv: (_ for _ in ()).throw(AssertionError("must not start QEMU")),
+    )
+
+    rc = cli._start_existing_vm_if_needed("vm1", "stopped", 60)
+
+    assert rc == 1
+    err = capsys.readouterr().err
+    assert missing_kernel in err
+    assert "sbx recreate vm1 --force" in err
+
+
 def test_failed_managed_run_hides_json_and_prints_hint(
     monkeypatch: pytest.MonkeyPatch,
     tmp_path: Path,