feat(compute): probe uBridge's swappable bridge TAP leg

The bridge module gained delete_nio_tap (uBridge's gns3server-integration
contract, section 'bridge — generic NIO relay with a swappable TAP leg'):
a per-port bridge can swap its topology leg between UDP and a persistent
TAP through stop -> delete -> add -> start, which is what lets an IOL
runner container's port bridge carry a kernel-link anchor.

The probe needs no scratch objects and no capabilities: one command
against a bridge that cannot exist — 202 (unknown command) is an old
build, 214 (bridge doesn't exist) is a new one. Cached by binary identity
like every other probe; any failure reports unknown.

GET /v3/compute/capabilities gains ubridge_bridge_tap; the controller's
default capability dict carries it too (the single schema definition, per
the 1e67fbf12 lesson).

tests/api/routes/compute/test_capabilities.py

@@ -43,6 +43,7 @@ class TestCapabilitiesRoutes:
         monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_tc_capabilities", no_probe)
         monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_tap_support", _no_tap_probe)
         monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_iol_tap_support", _no_tap_probe)
+        monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_bridge_tap_support", _no_tap_probe)
         response = await compute_client.get(app.url_path_for("compute:get_capabilities"))
         assert response.status_code == status.HTTP_200_OK
         assert response.json() == {
@@ -69,6 +70,7 @@ class TestCapabilitiesRoutes:
             "ubridge_tc": None,
             "ubridge_tap": None,
             "ubridge_iol_tap": None,
+            "ubridge_bridge_tap": None,
         }
 
     async def test_get_on_gns3vm(self, app: FastAPI, compute_client: AsyncClient, on_gns3vm, monkeypatch) -> None:
@@ -79,6 +81,7 @@ class TestCapabilitiesRoutes:
         monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_tc_capabilities", no_probe)
         monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_tap_support", _no_tap_probe)
         monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_iol_tap_support", _no_tap_probe)
+        monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_bridge_tap_support", _no_tap_probe)
         response = await compute_client.get(app.url_path_for("compute:get_capabilities"))
         assert response.status_code == status.HTTP_200_OK
         assert response.json() == {
@@ -105,6 +108,7 @@ class TestCapabilitiesRoutes:
             "ubridge_tc": None,
             "ubridge_tap": None,
             "ubridge_iol_tap": None,
+            "ubridge_bridge_tap": None,
         }
 
     async def test_get_reports_ubridge_tc(self, app: FastAPI, compute_client: AsyncClient, monkeypatch) -> None:
@@ -115,6 +119,7 @@ class TestCapabilitiesRoutes:
         monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_tc_capabilities", fake_probe)
         monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_tap_support", _no_tap_probe)
         monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_iol_tap_support", _no_tap_probe)
+        monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_bridge_tap_support", _no_tap_probe)
         response = await compute_client.get(app.url_path_for("compute:get_capabilities"))
         assert response.status_code == status.HTTP_200_OK
         assert response.json()["ubridge_tc"] == {
@@ -135,6 +140,7 @@ class TestCapabilitiesRoutes:
 
         monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_tap_support", fake_tap_probe)
         monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_iol_tap_support", _no_tap_probe)
+        monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_bridge_tap_support", _no_tap_probe)
         response = await compute_client.get(app.url_path_for("compute:get_capabilities"))
         assert response.status_code == status.HTTP_200_OK
         assert response.json()["ubridge_tap"] is True
@@ -153,3 +159,20 @@ class TestCapabilitiesRoutes:
         response = await compute_client.get(app.url_path_for("compute:get_capabilities"))
         assert response.status_code == status.HTTP_200_OK
         assert response.json()["ubridge_iol_tap"] is True
+
+    async def test_get_reports_ubridge_bridge_tap(self, app: FastAPI, compute_client: AsyncClient, monkeypatch) -> None:
+        """
+        The swappable-bridge-TAP-leg capability is what makes an IOL runner
+        container kernel-eligible, so it travels with the other compute
+        capabilities.
+        """
+
+        async def fake_bridge_tap_probe():
+            return True
+
+        monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_bridge_tap_support", fake_bridge_tap_probe)
+        monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_tap_support", _no_tap_probe)
+        monkeypatch.setattr("gns3server.api.routes.compute.capabilities.probe_iol_tap_support", _no_tap_probe)
+        response = await compute_client.get(app.url_path_for("compute:get_capabilities"))
+        assert response.status_code == status.HTTP_200_OK
+        assert response.json()["ubridge_bridge_tap"] is True