diff --git a/tests/test_github_installs.py b/tests/test_github_installs.py
index 907dd2e6..fd6afc66 100644
--- a/tests/test_github_installs.py
+++ b/tests/test_github_installs.py
@@ -215,6 +215,13 @@ def _slack_frame():
 async def test_one_hub_fans_out_to_both_adapters(monkeypatch):
     """THE step-3 invariant: slack + github share one relay socket; frames land
     on their own adapter by provider tag."""
+    # Stub name resolution at its chokepoint. A dead port only refuses instantly on
+    # POSIX; on Windows it takes ~2.0s per call and this frame makes two, blowing the
+    # 2.0s wait_dispatched budget below. The env var stays as a no-network backstop.
+    async def _no_slack_api(self, team_id, method, params):
+        return None
+
+    monkeypatch.setattr(SlackRelayAdapter, "_slack_get", _no_slack_api)
     monkeypatch.setenv("SLACK_API_URL", "http://127.0.0.1:9/")
     hub = RelayHub(
         "wss://relay.test/ws",
diff --git a/tests/test_slack_relay.py b/tests/test_slack_relay.py
index b05ce807..9894a8c0 100644
--- a/tests/test_slack_relay.py
+++ b/tests/test_slack_relay.py
@@ -20,9 +20,21 @@
 
 @pytest.fixture(autouse=True)
 def _no_slack_network(monkeypatch):
-    """Name/channel resolution is best-effort; unstubbed lookups must fail
-    instantly at a dead loopback port, never reach slack.com — a slow real
-    answer was blowing the 2s wait_dispatched window intermittently."""
+    """Name/channel resolution is best-effort, so stub it at its single chokepoint.
+
+    A dead loopback port alone is not enough. Refusing a connection is only instant
+    on POSIX; on Windows it takes ~2.0s, and `_dispatch_slack_event` awaits both
+    `_display_name` and `_channel_name`, so one frame cost ~4s against the 2.0s
+    budget and no frame ever dispatched in time. `SLACK_API_URL` still points at a
+    dead port as a backstop, so an unstubbed path can never reach slack.com.
+    """
+
+    async def _no_slack_api(self, team_id, method, params):
+        return None
+
+    monkeypatch.setattr(
+        relay_client.SlackRelayAdapter, "_slack_get", _no_slack_api
+    )
     monkeypatch.setenv("SLACK_API_URL", "http://127.0.0.1:9/")