diff --git a/plugins/platforms/slack/adapter.py b/plugins/platforms/slack/adapter.py
index 7ce10bb94814..e78d3c57524c 100644
--- a/plugins/platforms/slack/adapter.py
+++ b/plugins/platforms/slack/adapter.py
@@ -1131,10 +1131,34 @@ class SlackAdapter(BasePlatformAdapter):
             app_token = os.getenv("SLACK_APP_TOKEN")
 
         if not raw_token:
-            logger.error("[Slack] SLACK_BOT_TOKEN not set")
+            logger.error(
+                "[Slack] SLACK_BOT_TOKEN not set — this is a permanent config "
+                "error; set SLACK_BOT_TOKEN via `hermes gateway setup` "
+                "or in the active profile's ~/.hermes/.env file, then restart "
+                "the gateway.",
+            )
+            self._set_fatal_error(
+                "missing_slack_bot_token",
+                "SLACK_BOT_TOKEN not configured. Use `hermes gateway setup` "
+                "or add it to your active profile's ~/.hermes/.env file, "
+                "then restart the gateway.",
+                retryable=False,
+            )
             return False
         if not app_token:
-            logger.error("[Slack] SLACK_APP_TOKEN not set")
+            logger.error(
+                "[Slack] SLACK_APP_TOKEN not set — this is a permanent config "
+                "error; set SLACK_APP_TOKEN via `hermes gateway setup` "
+                "or in the active profile's ~/.hermes/.env file, then restart "
+                "the gateway.",
+            )
+            self._set_fatal_error(
+                "missing_slack_app_token",
+                "SLACK_APP_TOKEN not configured. Use `hermes gateway setup` "
+                "or add it to your active profile's ~/.hermes/.env file, "
+                "then restart the gateway.",
+                retryable=False,
+            )
             return False
 
         proxy_url = _resolve_slack_proxy_url()
diff --git a/tests/gateway/test_slack.py b/tests/gateway/test_slack.py
index 6f5488c03a4b..d8c25a4a9d04 100644
--- a/tests/gateway/test_slack.py
+++ b/tests/gateway/test_slack.py
@@ -5192,3 +5192,64 @@ class TestThreadContextAppMessages:
             )
 
         assert "hello" in content  # the real message survives; empty bot msg dropped
+
+
+# ---------------------------------------------------------------------------
+# Missing-credential handling — fatal-error contract
+# ---------------------------------------------------------------------------
+
+
+class TestMissingCredentials:
+    """Missing SLACK_BOT_TOKEN or SLACK_APP_TOKEN must set a non-retryable fatal error."""
+
+    @pytest.mark.asyncio
+    async def test_missing_bot_token_sets_fatal_error(self):
+        """When SLACK_BOT_TOKEN is absent from both config and env, connect()
+        must set fatal_error with code 'missing_slack_bot_token' and retryable=False."""
+        config = PlatformConfig(enabled=True, token=None)  # no bot token
+        adapter = SlackAdapter(config)
+
+        fatal_errors = []
+
+        def capture_fatal(code, message, *, retryable):
+            fatal_errors.append({"code": code, "message": message, "retryable": retryable})
+
+        with (
+            patch.object(adapter, "_set_fatal_error", side_effect=capture_fatal),
+            patch.dict(os.environ, {}, clear=True),
+        ):
+            result = await adapter.connect()
+
+        assert result is False
+        assert len(fatal_errors) == 1
+        assert fatal_errors[0]["code"] == "missing_slack_bot_token"
+        assert fatal_errors[0]["retryable"] is False
+        assert "SLACK_BOT_TOKEN" in fatal_errors[0]["message"]
+        assert "hermes gateway setup" in fatal_errors[0]["message"].lower() or ".env" in fatal_errors[0]["message"]
+
+    @pytest.mark.asyncio
+    async def test_missing_app_token_sets_fatal_error(self):
+        """When SLACK_APP_TOKEN is absent but SLACK_BOT_TOKEN is present,
+        connect() must set fatal_error with code 'missing_slack_app_token'
+        and retryable=False."""
+        config = PlatformConfig(enabled=True, token="xoxb-fake")
+        adapter = SlackAdapter(config)
+
+        fatal_errors = []
+
+        def capture_fatal(code, message, *, retryable):
+            fatal_errors.append({"code": code, "message": message, "retryable": retryable})
+
+        with (
+            patch.object(adapter, "_set_fatal_error", side_effect=capture_fatal),
+            patch.dict(os.environ, {"SLACK_BOT_TOKEN": "xoxb-fake"}, clear=True),
+        ):
+            result = await adapter.connect()
+
+        assert result is False
+        assert len(fatal_errors) == 1
+        assert fatal_errors[0]["code"] == "missing_slack_app_token"
+        assert fatal_errors[0]["retryable"] is False
+        assert "SLACK_APP_TOKEN" in fatal_errors[0]["message"]
+        assert "hermes gateway setup" in fatal_errors[0]["message"].lower() or ".env" in fatal_errors[0]["message"]
+