feat(server): add getUiCapability helper for capability negotiation (#313)

* feat(server): add hasUiSupport/getUiCapability for experimental+extensions

Support double-tagging for MCP Apps capability negotiation:
- Check both experimental and extensions fields in client capabilities
- Add hasUiSupport() to easily check if client supports MCP Apps
- Add getUiCapability() to retrieve the capability settings
- Update spec to document both capability locations

This enables forward compatibility as MCP transitions from experimental
to the extensions field (SEP-1724).

Claude-Generated-By: Claude Code (cli/claude-opus-4-5=100%)
Claude-Steers: 0
Claude-Permission-Prompts: 0
Claude-Escapes: 0

* fix: update @types/node version in package-lock.json

Replace invalid 22.19.5/22.19.6/22.19.7 versions with valid 22.19.3

* docs(spec): clarify hosts SHOULD double-tag, servers SHOULD check both

- Hosts SHOULD advertise capabilities in both experimental and extensions
- Servers SHOULD check both locations, preferring extensions when present
- Updated example to show double-tagging pattern

* chore: remove double-tagging recommendation, keep hasUiSupport helper

Reverts the spec changes that recommended clients double-tag capabilities
in both experimental and extensions fields. The helper functions remain
as they're useful for checking capability in either location.

* refactor(server): simplify to only getUiCapability, remove hasUiSupport

- Remove hasUiSupport function (use getUiCapability directly)
- Remove double-tagging logic (only check extensions field)
- Add ClientCapabilitiesWithExtensions type using SDK's ClientCapabilities
- Update spec to use getUiCapability
- Simplify tests

* fix: update @see link to getUiCapability

* refactor(server): inline ClientCapabilitiesWithExtensions type in getUiCapability

* refactor: move McpUiClientCapabilities to spec.types.ts

src/generated/schema.json

@@ -28,6 +28,20 @@
       },
       "additionalProperties": false
     },
+    "McpUiClientCapabilities": {
+      "$schema": "https://json-schema.org/draft/2020-12/schema",
+      "type": "object",
+      "properties": {
+        "mimeTypes": {
+          "description": "Array of supported MIME types for UI resources.\nMust include `\"text/html;profile=mcp-app\"` for MCP Apps support.",
+          "type": "array",
+          "items": {
+            "type": "string"
+          }
+        }
+      },
+      "additionalProperties": false
+    },
     "McpUiDisplayMode": {
       "$schema": "https://json-schema.org/draft/2020-12/schema",
       "anyOf": [

src/generated/schema.test.ts

@@ -119,6 +119,10 @@ export type McpUiToolMetaSchemaInferredType = z.infer<
   typeof generated.McpUiToolMetaSchema
 >;
 
+export type McpUiClientCapabilitiesSchemaInferredType = z.infer<
+  typeof generated.McpUiClientCapabilitiesSchema
+>;
+
 export type McpUiMessageRequestSchemaInferredType = z.infer<
   typeof generated.McpUiMessageRequestSchema
 >;
@@ -277,6 +281,12 @@ expectType<McpUiToolVisibilitySchemaInferredType>(
 );
 expectType<spec.McpUiToolMeta>({} as McpUiToolMetaSchemaInferredType);
 expectType<McpUiToolMetaSchemaInferredType>({} as spec.McpUiToolMeta);
+expectType<spec.McpUiClientCapabilities>(
+  {} as McpUiClientCapabilitiesSchemaInferredType,
+);
+expectType<McpUiClientCapabilitiesSchemaInferredType>(
+  {} as spec.McpUiClientCapabilities,
+);
 expectType<spec.McpUiMessageRequest>(
   {} as McpUiMessageRequestSchemaInferredType,
 );

src/generated/schema.ts

@@ -562,6 +562,26 @@ export const McpUiToolMetaSchema = z.object({
     ),
 });
 
+/**
+ * @description MCP Apps capability settings advertised by clients to servers.
+ *
+ * Clients advertise these capabilities via the `extensions` field in their
+ * capabilities during MCP initialization. Servers can check for MCP Apps
+ * support using {@link server-helpers!getUiCapability}.
+ */
+export const McpUiClientCapabilitiesSchema = z.object({
+  /**
+   * @description Array of supported MIME types for UI resources.
+   * Must include `"text/html;profile=mcp-app"` for MCP Apps support.
+   */
+  mimeTypes: z
+    .array(z.string())
+    .optional()
+    .describe(
+      'Array of supported MIME types for UI resources.\nMust include `"text/html;profile=mcp-app"` for MCP Apps support.',
+    ),
+});
+
 /**
  * @description Request to send a message to the host's chat interface.
  * @see {@link app!App.sendMessage `App.sendMessage`} for the method that sends this request