💻 refactor: Migrate MCP UI resources from index-based to ID-based referencing

- Replace index-based resource markers with stable resource IDs
- Update plugin to parse \ui{resourceId} format instead of \ui0
- Refactor components to use useMessagesOperations instead of useSubmitMessage
- Add ShareMessagesProvider for UI resources in share view
- Add useConversationUIResources hook for cross-turn resource lookups
- Update parsers to generate resource IDs from content hashes
- Update all tests to use resource IDs instead of indices
- Add sandbox permissions for iframe popups
- Remove deprecated MCP tool context instructions

api/app/clients/tools/util/handleTools.js

@@ -335,15 +335,6 @@ Current Date & Time: ${replaceSpecialVars({ text: '{{iso_datetime}}' })}
       };
       continue;
     } else if (tool && mcpToolPattern.test(tool)) {
-      toolContextMap[tool] = `# MCP Tool \`${tool}\`:
-      When this tool returns UI resources (URIs starting with "ui://"):
-      - You should usually introduce what you're showing before the marker
-      - For a single resource: \\ui0
-      - For multiple resources shown separately: \\ui0 \\ui1
-      - For multiple resources in a carousel: \\ui0,1,2
-      - The UI will be rendered inline where you place the marker
-      - Format: \\ui{index} or \\ui{index1,index2,index3} where indices are 0-based, in the order they appear in the tool response`;
-
       const [toolName, serverName] = tool.split(Constants.mcp_delimiter);
       if (toolName === Constants.mcp_server) {
         /** Placeholder used for UI purposes */