docs: add MCP Apps (SEP-1865) documentation
Integrate comprehensive documentation for MCP Apps, the first official
MCP extension enabling interactive UI delivery.
Changes:
- guide/architecture.md (656): New section "MCP Extensions: Apps"
- Technical architecture (primitives, SDK, security)
- Platform support (Claude Desktop, VS Code, ChatGPT, Goose)
- Example implementations (9 production tools at launch)
- Developer workflow and SDK usage
- ~150 lines of technical documentation
- guide/ultimate-guide.md (6509): New section "MCP Evolution: Apps"
- User context and use cases
- Available interactive tools (Asana, Slack, Figma, etc.)
- Platform support matrix
- Hybrid workflow examples
- ~90 lines of user-facing documentation
- guide/ultimate-guide.md (7522): Table update
- Added "Interactive UI" row to Plugin vs. MCP Server comparison
- Clarified MCP Apps = "What Claude can show"
- machine-readable/reference.yaml: 8 new entries
- mcp_apps_architecture, mcp_apps_evolution
- Links to spec, SDK, blog posts
- CLI relevance note (indirect)
- docs/resource-evaluations/mcp-apps-announcement.md: New evaluation
- Score: 4/5 (High Value - Integrate within 1 week)
- Fact-checked with Perplexity searches
- Technical review by agent
Resource evaluated:
- https://blog.modelcontextprotocol.io/posts/2026-01-26-mcp-apps/
- https://claude.com/blog/interactive-tools-in-claude
Total documentation: ~240 lines across 3 files
Score: 4/5 (High Value)
CLI relevance: Indirect (ecosystem understanding, MCP server dev, hybrid workflows)
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>
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