Detach graph viewer from MCP transport

tests/test_visualization.py

@@ -3,6 +3,7 @@ from __future__ import annotations
 import json
 import shutil
 import subprocess
+import sys
 import tempfile
 import time
 import unittest
@@ -270,6 +271,46 @@ if (nodePalette("child", 2).fill === nodePalette("child", 1).fill) fail("hop sha
             finally:
                 runner.stop()
 
+    def test_detached_worker_survives_the_launching_transport_process(self) -> None:
+        with tempfile.TemporaryDirectory() as directory:
+            root = self.copy_fixture("alpha", Path(directory))
+            ProjectIndex(Project.open(root)).build()
+            script = """
+import sys
+from pathlib import Path
+from docforge.index import ProjectIndex
+from docforge.project import Project
+from docforge.visualization import DetachedVisualizationRunner
+
+runner = DetachedVisualizationRunner(
+    ProjectIndex(Project.open(Path(sys.argv[1]))),
+    initial_grace_seconds=1.0,
+    lease_seconds=0.3,
+    monitor_interval_seconds=0.02,
+)
+print(runner.start()["url"], flush=True)
+time.sleep(60)
+"""
+            script = "import time\n" + script
+            with subprocess.Popen(
+                [sys.executable, "-c", script, str(root)],
+                stdout=subprocess.PIPE,
+                stderr=subprocess.PIPE,
+                text=True,
+            ) as launcher:
+                assert launcher.stdout is not None
+                url = launcher.stdout.readline().strip()
+                launcher.terminate()
+                launcher.wait(timeout=2)
+                self.assertLess(launcher.returncode, 0)
+            self.assertTrue(url.startswith("http://127.0.0.1:"))
+            with urllib.request.urlopen(url, timeout=2) as response:
+                self.assertEqual(200, response.status)
+
+            time.sleep(0.6)
+            with self.assertRaises(OSError):
+                urllib.request.urlopen(url, timeout=0.2)
+
     def test_runner_rejects_ambiguous_targets_and_changed_index_snapshot(self) -> None:
         with tempfile.TemporaryDirectory() as directory:
             root = self.copy_fixture("alpha", Path(directory))