Keep the platform level error message alongside the socket implementation check

esphome/components/api/__init__.py

@@ -295,11 +295,17 @@ def _consume_api_sockets(config: ConfigType) -> ConfigType:
 
 
 def _validate_outgoing_connection(config: ConfigType) -> ConfigType:
-    # The socket-layer constraint (raw lwip_tcp cannot dial out, the default
-    # on esp8266/rp2040) is checked against the resolved implementation in
-    # _validate_outgoing_socket_implementation at final validate
     if CONF_OUTGOING_CONNECTION not in config:
         return config
+    # Platform default check here for a friendly early error; an explicit
+    # lwip_tcp selection on other platforms is caught against the resolved
+    # implementation in _validate_outgoing_socket_implementation
+    if CORE.is_esp8266 or CORE.is_rp2:
+        raise cv.Invalid(
+            "outgoing_connection is not supported on this platform because its "
+            "socket layer cannot make outgoing connections",
+            path=[CONF_OUTGOING_CONNECTION],
+        )
     if CONF_ENCRYPTION not in config:
         raise cv.Invalid(
             "outgoing_connection requires 'encryption' so the peer is verified by key",
@@ -472,7 +478,7 @@ def _validate_outgoing_socket_implementation(config: ConfigType) -> ConfigType:
 
 
 def _validate_outgoing_host_ipv6(config: ConfigType) -> ConfigType:
-    """An IPv6 host silently dials 255.255.255.255 on a build without IPv6."""
+    """An IPv6 host can never be parsed, so never dialed, without IPv6."""
     if (
         (outgoing := config.get(CONF_OUTGOING_CONNECTION)) is None
         or (host := outgoing.get(CONF_HOST)) is None

tests/component_tests/api/test_outgoing_connection.py

@@ -67,20 +67,15 @@ def test_outgoing_connection_rejected_on_raw_lwip_platforms(
     set_core_config: SetCoreConfigCallable,
     platform_framework: PlatformFramework,
 ) -> None:
-    """esp8266 and rp2040 default to lwip_tcp and are rejected at final validate."""
-    set_core_config(
-        platform_framework,
-        full_config={"socket": {"implementation": "lwip_tcp"}},
-    )
-    config = CONFIG_SCHEMA(_api_config({"host": "192.168.1.2"}))
-    with pytest.raises(cv.Invalid, match="lwip_tcp"):
-        _validate_outgoing_socket_implementation(config)
+    set_core_config(platform_framework)
+    with pytest.raises(cv.Invalid, match="not supported on this platform"):
+        CONFIG_SCHEMA(_api_config({"host": "192.168.1.2"}))
 
 
-def test_outgoing_connection_rejects_lwip_tcp_socket(
+def test_outgoing_connection_rejects_lwip_tcp_selected_on_esp32(
     set_core_config: SetCoreConfigCallable,
 ) -> None:
-    """An explicit lwip_tcp socket selection is rejected at final validate."""
+    """An explicit lwip_tcp selection is caught at final validate."""
     set_core_config(
         PlatformFramework.ESP32_IDF,
         platform_data=ESP32_PLATFORM_DATA,