Mcp Apps 3 : Integrate MCP Apps Sample Agent into Orchestrator Sample

[sugoi-yuzuru]

Description

This PR incorporates the MCP Apps demo into the Angular Orchestrator Sample.
It completes the following 3 staged PRs into a demo.

0: #791 introduced a new Calculator App resource in the Sample MCP Server
1: #801 introduced a new A2UI Angular Component McpApps that can containerize and display MCP Apps resrource as a A2UI Component/
2: #815 set up a standalone A2A Agent that show cases how the relay of MCP Apps retrieved from MCP Servers can be translated into A2UI protocol for A2UI client consumption.

and then 3: this PR updates the existing Orchestrator A2UI demo to integrate with the A2A Agent prepared in #2.

See demo: https://screencast.googleplex.com/cast/NTU3NTU5MTg4MDI5NDQwMHxhZTA1OGM1Mi1kNg

Pre-launch Checklist

• I signed the CLA.
• I read the Contributors Guide.
• I read the Style Guide.
• I have added updates to the CHANGELOG.
• I updated/added relevant documentation.
• My code changes (if any) have tests.

If you need help, consider asking for advice on the discussion board.

[gemini-code-assist]

Code Review

This pull request successfully integrates the MCP Apps demo into the Angular Orchestrator Sample by adding a new mcp_app_proxy agent and the corresponding client-side components. The implementation uses a sandboxed iframe approach for rendering MCP apps, which is a good security practice.

My review includes a critical security recommendation regarding the sandbox implementation, along with several medium-severity suggestions to improve code quality and maintainability by removing unused imports and addressing minor issues in documentation and code style. Overall, the changes are well-structured and the new sample is a valuable addition.

[gemini-code-assist]

The TODO comment correctly identifies a critical security risk. Loading the sandbox iframe from the same origin (sandbox_iframe/sandbox.html) significantly reduces the security benefits of the sandbox attribute, as same-origin iframes have ways to bypass some restrictions. For robust security, the sandbox content should be served from a completely separate origin (e.g., sandbox.example.com). This should be prioritized to prevent potential cross-site scripting (XSS) vulnerabilities where the sandboxed content could affect the main application.