Preserve MCP App UI metadata in tool-call events and history (#45805)

## Why

Clients need widget presentation details to render MCP Apps without waiting for the full MCP catalog, including when replaying saved history.

## What changed

- Add `mcpToolCall.mcpAppUi` with the invoked descriptor's `resourceUri` and `preferredModelDisplayMode`, and carry it through tool-call events and saved history.
- Support `fullscreen` and default to `inline` when the display preference is missing or unsupported.
- Keep existing resource URI fields for compatibility. Leave `mcpAppUi` null for older history and tools that declare widgets only in result metadata, where clients still use catalog discovery.
- Update protocol schemas, TypeScript and Python types, and app-server documentation.

## Testing

Add parameterized integration coverage for fullscreen, missing and unsupported preferences, legacy URI metadata, and result-only widgets, verifying consistent tool events and preservation across session resume.

GitOrigin-RevId: 2a9bed804dcea8c2b4903b8406fa6710681f7f5e

codex-rs/app-server-protocol/schema/json/v2/ThreadMetadataUpdateResponse.json

@@ -676,6 +676,29 @@
     "LegacyAppPathString": {
       "type": "string"
     },
+    "McpAppDisplayMode": {
+      "enum": [
+        "inline",
+        "fullscreen"
+      ],
+      "type": "string"
+    },
+    "McpAppUi": {
+      "description": "UI resource and display preference for model invocations, captured from the tool descriptor.",
+      "properties": {
+        "preferredModelDisplayMode": {
+          "$ref": "#/definitions/McpAppDisplayMode"
+        },
+        "resourceUri": {
+          "type": "string"
+        }
+      },
+      "required": [
+        "preferredModelDisplayMode",
+        "resourceUri"
+      ],
+      "type": "object"
+    },
     "McpToolCallAppContext": {
       "properties": {
         "actionName": {
@@ -1730,12 +1753,23 @@
               "type": "string"
             },
             "mcpAppResourceUri": {
-              "description": "Deprecated: use `appContext.resourceUri` instead.",
+              "description": "Legacy compatibility field; prefer `mcpAppUi.resourceUri` when available.",
               "type": [
                 "string",
                 "null"
               ]
             },
+            "mcpAppUi": {
+              "anyOf": [
+                {
+                  "$ref": "#/definitions/McpAppUi"
+                },
+                {
+                  "type": "null"
+                }
+              ],
+              "description": "Presentation captured from the invoked descriptor; absent in older history."
+            },
             "pluginId": {
               "type": [
                 "string",