Enable streaming when only streaming.mode is set

- StreamingConfig.from_dict now treats `mode` as an alias for `transport`
  that also implies `enabled`, so `streaming: {mode: auto}` turns streaming
  on instead of being silently ignored (enabled defaulted to False, which
  buffered the whole reply and sent it in one message)
- `mode: off` disables streaming; an explicit `enabled` key still wins; an
  explicit `transport` takes precedence over `mode`
- Add regression tests covering mode/transport/enabled precedence and the
  real-world `mode + preloader_frames` block

gateway/config.py

@@ -717,9 +717,35 @@ class StreamingConfig:
     def from_dict(cls, data: Dict[str, Any]) -> "StreamingConfig":
         if not isinstance(data, dict) or not data:
             return cls()
+
+        # ``mode`` is an ergonomic alias for the transport that ALSO implies
+        # ``enabled``.  A config like ``streaming: {mode: auto}`` reads as
+        # "turn streaming on, transport=auto" — matching the natural intent
+        # of someone enabling streaming without also spelling out
+        # ``enabled: true``.  Without this, ``mode`` was silently ignored and
+        # streaming stayed disabled (``enabled`` defaults to False), which is
+        # a surprising footgun: the whole reply buffers and sends at once.
+        # ``mode: off`` disables streaming; an explicit ``enabled`` key always
+        # wins so callers can force either state.
+        raw_transport = data.get("transport")
+        raw_mode = data.get("mode")
+        transport = raw_transport if raw_transport is not None else raw_mode
+        if transport is None:
+            transport = "auto"
+        transport = str(transport).strip().lower() or "auto"
+
+        if "enabled" in data:
+            enabled = _coerce_bool(data.get("enabled"), False)
+        elif raw_mode is not None or raw_transport is not None:
+            # A mode/transport was given without an explicit enabled flag:
+            # infer enabled from the transport ("off" = disabled, else on).
+            enabled = transport != "off"
+        else:
+            enabled = False
+
         return cls(
-            enabled=_coerce_bool(data.get("enabled"), False),
-            transport=data.get("transport", "auto"),
+            enabled=enabled,
+            transport=transport,
             edit_interval=_coerce_float(
                 data.get("edit_interval"), DEFAULT_STREAMING_EDIT_INTERVAL,
             ),

tests/test_gateway_streaming_nested_config.py

@@ -41,3 +41,71 @@ class TestStreamingConfigNested:
         })
         assert cfg.streaming.enabled is True
         assert cfg.streaming.transport == "edit"
+
+
+class TestStreamingModeAlias:
+    """``streaming: {mode: ...}`` is an alias that also implies ``enabled``.
+
+    Regression for a live config footgun: ``streaming: {mode: auto}`` was
+    silently ignored (mode was never read), so streaming stayed disabled and
+    the whole reply buffered before the first Telegram send.
+    """
+
+    def test_mode_auto_enables_streaming(self):
+        from gateway.config import StreamingConfig
+
+        sc = StreamingConfig.from_dict({"mode": "auto"})
+        assert sc.enabled is True
+        assert sc.transport == "auto"
+
+    def test_mode_edit_enables_streaming(self):
+        from gateway.config import StreamingConfig
+
+        sc = StreamingConfig.from_dict({"mode": "edit"})
+        assert sc.enabled is True
+        assert sc.transport == "edit"
+
+    def test_mode_off_disables_streaming(self):
+        from gateway.config import StreamingConfig
+
+        sc = StreamingConfig.from_dict({"mode": "off"})
+        assert sc.enabled is False
+        assert sc.transport == "off"
+
+    def test_mode_with_extra_keys_still_enables(self):
+        """Real-world block: mode plus unrelated preloader_frames."""
+        from gateway.config import StreamingConfig
+
+        sc = StreamingConfig.from_dict(
+            {"mode": "auto", "preloader_frames": ["a", "b"]}
+        )
+        assert sc.enabled is True
+        assert sc.transport == "auto"
+
+    def test_explicit_enabled_overrides_mode(self):
+        from gateway.config import StreamingConfig
+
+        sc = StreamingConfig.from_dict({"mode": "auto", "enabled": False})
+        assert sc.enabled is False
+        # transport still resolves from mode
+        assert sc.transport == "auto"
+
+    def test_transport_takes_precedence_over_mode(self):
+        from gateway.config import StreamingConfig
+
+        sc = StreamingConfig.from_dict({"mode": "off", "transport": "draft"})
+        assert sc.transport == "draft"
+        assert sc.enabled is True
+
+    def test_empty_block_stays_disabled(self):
+        from gateway.config import StreamingConfig
+
+        sc = StreamingConfig.from_dict({})
+        assert sc.enabled is False
+
+    def test_transport_only_enables(self):
+        from gateway.config import StreamingConfig
+
+        sc = StreamingConfig.from_dict({"transport": "edit"})
+        assert sc.enabled is True
+        assert sc.transport == "edit"