Companion keeper: after a restart the panel opens the Companion that ran last if it is not running

- only in the watchdog's first 10 minutes, never another version, never during an upgrade
- SC verified end to end; laptop SSH to the SC Macs; configs synced

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_status_panel.py

@@ -2581,3 +2581,38 @@ class TestSwitches(unittest.TestCase):
         errors = schema.validate(bad)[0]
         self.assertTrue(any("bypass.peers" in e for e in errors))
         self.assertTrue(any("nowhere" in e for e in errors))
+
+
+class TestCompanionKeeper(unittest.TestCase):
+    """After a restart the panel opens the Companion that ran last, and only then (Southcoast, 2026-10-21)."""
+
+    def setUp(self):
+        self.engine = sp.Engine(CONFIG, os.path.join(tempfile.mkdtemp(), "state.json"))
+        self.data = tempfile.mkdtemp()
+        self.app = tempfile.mkdtemp(suffix=".app")                       # stands in for /Applications/Companion 5.0.7.app
+        self.opened = []
+        self.now = 1000.0
+        self.running = self.app
+
+    def keeper(self):
+        return sp.CompanionKeeper(self.engine, self.data, started=self.now, running=lambda: self.running,
+                                  opener=self.opened.append)
+
+    def test_it_remembers_the_running_copy_and_opens_it_after_a_restart(self):
+        self.keeper().check(self.now)                                       # Companion running: remembered
+        self.assertEqual(self.engine.state.get("companion_app"), self.app)
+        self.running = None                                                # the Mac restarted without Companion
+        k = self.keeper()
+        self.assertEqual(k.check(self.now + 30), self.app)
+        self.assertEqual(k.check(self.now + 60), None)                      # not again straight away
+        self.assertEqual(self.opened, [self.app])
+
+    def test_it_never_acts_later_on_or_during_an_upgrade_or_without_knowing_the_copy(self):
+        k = self.keeper()
+        self.running = None
+        self.assertIsNone(k.check(self.now + 30))                           # never seen one: no guessing
+        self.engine.state.set("companion_app", self.app)
+        self.assertIsNone(k.check(self.now + 700))                          # someone quit it later on: left alone
+        open(os.path.join(self.data, "companion-upgrading"), "w").write("x")
+        self.assertIsNone(self.keeper().check(self.now + 30))               # an upgrade is going on
+        self.assertEqual(self.opened, [])