feat: add cluster context support in Compose with x-context extension

website/docs/4-guides/1-deployments/1-deploy-app.md

@@ -322,6 +322,24 @@ Choose unique names to avoid conflicts with services deployed from other Compose
 
 :::
 
+## Deploy to a specific cluster context
+
+If you manage multiple clusters, you can set `x-context` in your Compose file to make sure it always deploys to the
+correct one. You won't need to remember to manually switch clusters with `uc ctx` or `--context`.
+
+```yaml title="compose.yaml"
+x-context: prod
+
+services:
+  web:
+    image: myapp:latest
+```
+
+With this configuration, `uc deploy` and other commands using the Compose file will always target the `prod` context,
+regardless of your currently active context. You can still override it with the `--context` flag if needed.
+
+See [`x-context`](../../8-compose-file-reference/1-support-matrix.md#x-context) for more details.
+
 ## Use a different Compose file location
 
 If your Compose file has a different name or location, use the `-f/--file` flag to specify its path:

website/docs/8-compose-file-reference/1-support-matrix.md

@@ -72,6 +72,7 @@ If you rely on a specific Compose feature that is not supported by Uncloud, plea
 | External configs    | ❌ Not supported    | Not supported                                                                                                  |
 | Short syntax        | ❌ Not supported    | Use long syntax only                                                                                           |
 | **Extensions**      |                    |                                                                                                                |
+| `x-context`         | ✅ Uncloud-specific | Cluster context override                                                                                       |
 | `x-caddy`           | ✅ Uncloud-specific | Custom Caddy configuration                                                                                     |
 | `x-machines`        | ✅ Uncloud-specific | Machine placement constraints                                                                                  |
 | `x-ports`           | ✅ Uncloud-specific | Service port publishing                                                                                        |
@@ -86,6 +87,25 @@ If you rely on a specific Compose feature that is not supported by Uncloud, plea
 
 Uncloud provides several custom extensions to enhance the Compose experience:
 
+### `x-context`
+
+Set the cluster context for all commands that use the Compose file, such as `deploy`, `build`, and `logs`. This is
+useful when you manage multiple clusters and want to make sure a Compose file is always deployed to the right one.
+No need to remember to manually switch clusters with `uc ctx` or `--context`.
+
+`x-context` is a top-level key, not a service-level attribute.
+
+```yaml
+x-context: prod
+
+services:
+  web:
+    image: nginx
+```
+
+The `--context` and `--connect` flags take precedence over `x-context`. If you don't specify any of these, the current
+context from your Uncloud config (`--uncloud-config`) is used.
+
 ### `x-ports`
 
 Expose HTTP/HTTPS service ports via the Caddy reverse proxy, or bind TCP/UDP ports directly to the host: