feat(update): treat the testing channel as docker-only in the update check

A testing-<sha> build has no Gitea releases (the testing workflow builds only
a Docker image), so the in-app update check must not fall through to the
stable path - which would wrongly offer a stable "update". handle_api_update_check
now short-circuits for a "testing" version with docker_only:true and nothing
to update (no Gitea round-trip at all), and handle_api_update_apply refuses
self-update on the testing channel the same way it already does for nightly.

Two new tests cover both.

bridge_endpoints.py

@@ -2357,6 +2357,21 @@ class EndpointsMixin:
 
     async def handle_api_update_check(self, request):
         current = self._read_version()
+        # Testing channel (testing-<sha>) has no Gitea releases at all - it's
+        # a Docker-only channel. Report that directly instead of falling
+        # through to the stable path (which would wrongly offer a stable
+        # "update"). The :testing image is rolling, so there's nothing to
+        # compare a version against.
+        if "testing" in current:
+            return web.json_response({
+                "current":          current,
+                "latest":           current,
+                "update_available": False,
+                "tag":              current,
+                "docker_only":      True,
+                "changelog":        "Testing channel - updates are delivered via Docker: "
+                                    "docker compose pull && docker compose up -d",
+            })
         is_nightly = "nightly" in current
         is_dev = "-dev+" in current
         if is_nightly:
@@ -2441,9 +2456,11 @@ class EndpointsMixin:
         except Exception:
             return web.json_response({"error": "invalid json"}, status=400)
         new_tag = data.get("tag", "")
-        if "nightly" in self._read_version():
+        _cur = self._read_version()
+        if "nightly" in _cur or "testing" in _cur:
+            channel = "testing" if "testing" in _cur else "nightly"
             return web.json_response(
-                {"error": "nightly updates are delivered via Docker: "
+                {"error": f"{channel} updates are delivered via Docker: "
                           "docker compose pull && docker compose up -d"}, status=400)
         if getattr(sys, "frozen", False):
             return web.json_response(

tests/test_update_check.py

@@ -21,6 +21,43 @@ async def test_update_apply_invalid_json_returns_400(client):
     assert resp.status == 400
 
 
+@pytest.mark.asyncio
+async def test_update_check_testing_channel_is_docker_only(client):
+    """A testing-<sha> build has no Gitea releases at all - the check must
+    report a docker-only channel with nothing to update, NOT fall through to
+    the stable path and wrongly offer a stable "update". Must not even call
+    the Gitea API."""
+    c, bridge = client
+    bridge._read_version = lambda: "testing-2e4dbf0"
+
+    # Patch the API so that if the handler wrongly tried to fetch releases,
+    # the test would notice (mock returns something, but the handler must not
+    # reach it).
+    with patch("aiohttp.ClientSession.get") as mock_get:
+        resp = await c.get("/api/update/check")
+        data = await resp.json()
+
+    assert resp.status == 200
+    assert data["update_available"] is False
+    assert data["docker_only"] is True
+    assert data["current"] == "testing-2e4dbf0"
+    mock_get.assert_not_called()  # no Gitea round-trip for the testing channel
+
+
+@pytest.mark.asyncio
+async def test_update_apply_testing_channel_blocked(client):
+    """Self-update must be refused on the testing channel, same as nightly -
+    testing images are delivered via Docker only."""
+    c, bridge = client
+    bridge._read_version = lambda: "testing-2e4dbf0"
+
+    resp = await c.post("/api/update/apply", json={"tag": "whatever"})
+    data = await resp.json()
+    assert resp.status == 400
+    assert "testing" in data["error"]
+    assert "docker" in data["error"].lower()
+
+
 def _fake_releases_response(payload):
     resp = MagicMock()
     resp.status = 200