docs: add tool visibility and restructure _meta.ui (#131)

* docs: add tool visibility and restructure _meta.ui

- Restructure tool metadata: `_meta["ui/resourceUri"]` → `_meta.ui.resourceUri`
- Add `visibility` array field: ["model"], ["apps"], or ["model", "apps"]
- Default ["model"] preserves standard MCP behavior
- ["apps"] enables widget-only tools hidden from agent
- Add McpUiToolMeta interface for type safety
- Add Design Decision #4 explaining approach vs OpenAI's two-field model

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Co-Authored-By: Claude <noreply@anthropic.com>

* address PR review comments

- Change default visibility to ["model", "apps"]
- Add deprecation notice for flat ui/resourceUri format
- Add McpUiToolMeta and McpUiToolVisibility to spec.types.ts
- Improve tools/list and tools/call behavior wording

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Co-Authored-By: Claude <noreply@anthropic.com>

* chore: regenerate schemas for McpUiToolMeta types

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Co-Authored-By: Claude <noreply@anthropic.com>

* feat: tool visibility and nested _meta.ui format

- Rename visibility "apps" → "app" in McpUiToolVisibility type
- Add _meta.ui.resourceUri nested format (deprecate flat format)
- Add getToolUiResourceUri() utility with backward compatibility
- Add visibility demo to system-monitor-server:
  - get-system-stats: visibility ["model"] with resourceUri
  - refresh-stats: visibility ["app"] (app-only polling)
- Update all example servers to use new _meta.ui format
- Add 11 unit tests for getToolUiResourceUri()

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Co-Authored-By: Claude <noreply@anthropic.com>

* chore: regenerate schemas with updated dependencies

* feat: export McpUiToolMeta type and add type annotations

- Export McpUiToolMeta and McpUiToolVisibility types from types.ts
- Export corresponding Zod schemas (McpUiToolMetaSchema, McpUiToolVisibilitySchema)
- Add `as McpUiToolMeta` type annotations to all example servers
- Update docs/quickstart.md with proper typing

Ensures type safety for `_meta.ui` tool metadata across the codebase.

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Co-Authored-By: Claude <noreply@anthropic.com>

* feat: add server helpers and optional connect() transport

Add `src/server/` with convenience functions for registering MCP App tools
and resources:

- `registerAppTool(server, name, config, handler)`
- `registerAppResource(server, name, uri, config, callback)`

The `transport` parameter in `App.connect()` is now optional, defaulting to
`PostMessageTransport(window.parent)`.

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Co-Authored-By: Claude <noreply@anthropic.com>

* Update src/server/index.ts

Co-authored-by: Jonathan Hefner <jonathan@hefner.pro>

* feat: update McpUiAppToolConfig to support both _meta.ui and flat formats

* refactor: simplify server helper imports

* docs: add deprecation notice and improve resourceUri documentation

* feat: add backward compat normalization in registerAppTool

- If _meta.ui.resourceUri is set, also set legacy flat key
- If legacy flat key is set, also set _meta.ui.resourceUri
- Preserves existing visibility when merging
- Does not overwrite if both formats already set

* refactor: avoid mutating config arg in registerAppTool

* style: format with prettier

---------

Co-authored-by: Claude <noreply@anthropic.com>
Co-authored-by: Olivier Chafik <ochafik@anthropic.com>
Co-authored-by: Jonathan Hefner <jonathan@hefner.pro>

src/server/index.ts

@@ -8,6 +8,7 @@ import {
   RESOURCE_URI_META_KEY,
   RESOURCE_MIME_TYPE,
   McpUiResourceMeta,
+  McpUiToolMeta,
 } from "../app.js";
 import type {
   McpServer,
@@ -38,25 +39,31 @@ export interface ToolConfig {
  */
 export interface McpUiAppToolConfig extends ToolConfig {
   _meta: {
-    // Soon: `ui: McpUiToolMeta;` (https://github.com/modelcontextprotocol/ext-apps/pull/131)
-
-    /**
-     * URI of the UI resource to display for this tool.
-     * This is converted to `_meta["ui/resourceUri"]`.
-     *
-     * @example "ui://weather/widget.html"
-     */
-    [RESOURCE_URI_META_KEY]: string;
     [key: string]: unknown;
-  };
+  } & (
+    | {
+        ui: McpUiToolMeta;
+      }
+    | {
+        /**
+         * URI of the UI resource to display for this tool.
+         * This is converted to `_meta["ui/resourceUri"]`.
+         *
+         * @example "ui://weather/widget.html"
+         *
+         * @deprecated Use `_meta.ui.resourceUri` instead.
+         */
+        [RESOURCE_URI_META_KEY]?: string;
+      }
+  );
 }
 
 /**
  * MCP App Resource configuration for `registerAppResource`.
  */
 export interface McpUiAppResourceConfig extends ResourceMetadata {
-  _meta?: {
-    ui?: McpUiResourceMeta;
+  _meta: {
+    ui: McpUiResourceMeta;
     [key: string]: unknown;
   };
 }
@@ -95,7 +102,23 @@ export function registerAppTool(
   config: McpUiAppToolConfig,
   handler: ToolCallback<ZodRawShape>,
 ): void {
-  server.registerTool(name, config, handler);
+  // Normalize metadata for backward compatibility:
+  // - If _meta.ui.resourceUri is set, also set the legacy flat key
+  // - If the legacy flat key is set, also set _meta.ui.resourceUri
+  const meta = config._meta;
+  const uiMeta = meta.ui as McpUiToolMeta | undefined;
+  const legacyUri = meta[RESOURCE_URI_META_KEY] as string | undefined;
+
+  let normalizedMeta = meta;
+  if (uiMeta?.resourceUri && !legacyUri) {
+    // New format -> also set legacy key
+    normalizedMeta = { ...meta, [RESOURCE_URI_META_KEY]: uiMeta.resourceUri };
+  } else if (legacyUri && !uiMeta?.resourceUri) {
+    // Legacy format -> also set new format
+    normalizedMeta = { ...meta, ui: { ...uiMeta, resourceUri: legacyUri } };
+  }
+
+  server.registerTool(name, { ...config, _meta: normalizedMeta }, handler);
 }
 
 /**