[network] Document priority list for multi-interface support

src/content/docs/components/ethernet.mdx

@@ -10,7 +10,7 @@ This ESPHome component enables *wired* Ethernet connections for ESP32 and RP2040
 - **ESP32**: Supports RMII PHY chips (LAN8720, RTL8201, etc.) and SPI Ethernet chips (W5500, DM9051, ENC28J60).
 - **RP2040/RP2350**: Supports SPI/PIO Ethernet chips (W5100, W5500, W6100, W6300, ENC28J60).
 
-This component and the Wi-Fi component may **not** be used simultaneously, even if both are physically available.
+On ESP32 family devices, Ethernet may be configured alongside [WiFi](/components/wifi/) in the same configuration; see [Multi-Interface Support](/components/network/#multi-interface-support) on the [Network](/components/network/) component for how to control which interface ESPHome prefers. On RP2040, only one network interface may be configured at a time.
 
 ```yaml
 # Example configuration entry for RMII chips

src/content/docs/components/network.mdx

@@ -19,6 +19,7 @@ network:
 - **enable_ipv6** (*Optional*, boolean): Enables IPv6 support. Defaults to `false`.
 - **min_ipv6_addr_count** (*Optional*, integer): ESPHome considers the network to be connected when it has one IPv4 address and this number of IPv6 addresses. Defaults to `0` so as to not hang on boot with networks where IPv6 is not enabled. `2` is typically a reasonable value for configurations requiring IPv6.
 - **enable_high_performance** (*Optional*, boolean): Explicitly enables or disables high-performance networking optimizations. Only supported on ESP32 devices. When not specified, this is automatically enabled by components that benefit from optimized network settings. Set to `false` to disable these optimizations if they cause memory issues on your device. Defaults to component-driven behavior.
+- **priority** (*Optional*, list): Order in which network interfaces are brought up at boot. Each list entry names one of the supported interface types (`ethernet`, `wifi`, `openthread`, or `modem`) and may optionally specify a per-interface `timeout`. See [Multi-Interface Support](#multi-interface-support).
 
 ## High-performance networking
 
@@ -47,6 +48,39 @@ The optimization level depends on whether PSRAM is guaranteed to be available (c
 > This has various security and privacy implications decribed in [RFC7721](https://datatracker.ietf.org/doc/rfc7721/), as this might leak outside of the smart home network and makes the device uniquely identifiable.
 > Therefore, the address generation does not comply to [RFC7217](https://datatracker.ietf.org/doc/rfc7217/).
 
+## Multi-Interface Support
+
+Devices with more than one network interface — for example an ESP32 with both [WiFi](/components/wifi/) and SPI [Ethernet](/components/ethernet/) — can declare a `priority` list to control the order in which interfaces are brought up at boot and which one ESPHome prefers when more than one is connected.
+
+```yaml
+network:
+  priority:
+    - ethernet
+    - wifi
+```
+
+In the example above, Ethernet is started first and used as the default route while it is connected; WiFi is started afterwards and is used only if Ethernet is unavailable. The first entry in the list is the most-preferred interface.
+
+Each entry may either be a plain interface name or a mapping with an optional per-interface `timeout`:
+
+```yaml
+network:
+  priority:
+    - ethernet:
+        timeout: 30s
+    - wifi
+```
+
+The `timeout` value bounds how long ESPHome waits for that interface to come up before starting the next one in the list. It accepts the usual ESPHome [time format](/guides/configuration-types/#time) (for example `30s`, `1min`, `500ms`). A plain integer is interpreted as seconds. When omitted, ESPHome waits indefinitely for that interface.
+
+### Configuration variables (priority entries)
+
+- **interface** (**Required**, string): One of `ethernet`, `wifi`, `openthread`, or `modem`. The entry is written as the interface name itself (either as a string list item or as the single key of a mapping). Each interface may appear at most once. Every interface named here must also have its own top-level component block configured.
+- **timeout** (*Optional*, [Time](/guides/configuration-types/#time)): How long to wait for this interface to come up before moving on to the next one in the list. Defaults to waiting indefinitely.
+
+> [!NOTE]
+> Not every combination of interfaces is supported on every chip. WiFi and Ethernet may be used together on ESP32 family devices that have the necessary memory headroom; OpenThread and modem support depend on additional hardware and may be limited to specific variants. If `priority` is omitted, behavior is unchanged from earlier ESPHome releases and only a single interface component may be configured.
+
 ## See Also
 
 - [WiFi Component](/components/wifi/)

src/content/docs/components/wifi.mdx

@@ -6,9 +6,10 @@ import APIRef from '@components/APIRef.astro';
 
 
 This core ESPHome component sets up WiFi connections to access points
-for you. You need to have a network configuration (either Wifi or Ethernet)
-or ESPHome will fail in the config validation stage. You also can't have both Wifi
-and Ethernet setup in same time (even if your ESP has both wired).
+for you. You need to have a network configuration (either WiFi or [Ethernet](/components/ethernet/))
+or ESPHome will fail in the config validation stage.
+
+On ESP32 family devices, WiFi may be configured alongside [Ethernet](/components/ethernet/) in the same configuration; see [Multi-Interface Support](/components/network/#multi-interface-support) on the [Network](/components/network/) component for how to control which interface ESPHome prefers. On other platforms only one network interface may be configured at a time.
 
 It's recommended to provide a static IP for your node, as it can
 dramatically improve connection times.