fix: register opencode image understanding

extensions/opencode/openclaw.plugin.json

@@ -20,6 +20,17 @@
       "cliDescription": "OpenCode API key (Zen catalog)"
     }
   ],
+  "contracts": {
+    "mediaUnderstandingProviders": ["opencode"]
+  },
+  "mediaUnderstandingProviderMetadata": {
+    "opencode": {
+      "capabilities": ["image"],
+      "defaultModels": {
+        "image": "gpt-5-nano"
+      }
+    }
+  },
   "configSchema": {
     "type": "object",
     "additionalProperties": false,

extensions/opencode/plugin-registration.contract.test.ts

@@ -0,0 +1,8 @@
+import { describePluginRegistrationContract } from "../../test/helpers/plugins/plugin-registration-contract.js";
+
+describePluginRegistrationContract({
+  pluginId: "opencode",
+  providerIds: ["opencode"],
+  mediaUnderstandingProviderIds: ["opencode"],
+  requireDescribeImages: true,
+});