feat: limited MCP App support

[RomneyDa]

note, most new lines are in package lock. this is a 400 line PR

Adds MCP Apps support for continue

• When tools load checks _meta for ui info, and after tool call reads UI resource and injects in iframe
• There are a bunch of bugs when trying to use mcp-ui components within VS Code (or at least I couldn't figure it out) so I just made a fresh iframe
• Supports limited app interactivity
  • open link
  • add message to chat and stream
  • call tool (for now only works for tools from the same mcp server)
  • log to console
• Not supported yet
  • list resources
  • read resource
  • update model context

Example MCP configs to test:

{
  "mcpServers": {
    "threejs": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-threejs",
        "--stdio"
      ]
    }
  }
}

{
  "mcpServers": {
    "basic-react": {
      "command": "npx",
      "args": [
        "-y",
        "--silent",
        "--registry=https://registry.npmjs.org/",
        "@modelcontextprotocol/server-basic-react",
        "--stdio"
      ]
    }
  }
}

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Summary by cubic

Adds MCP App support so MCP tools can render interactive UIs inside Continue. The UI is loaded from the tool’s MCP UI resource and shown in a secure iframe with a postMessage bridge.

• New Features

  • Loads UI from tool _meta.ui.resourceUri or _meta["ui/resourceUri"], fetches via MCP readResource, and renders in a srcdoc iframe using ext-apps AppBridge/PostMessage with CSP/permission hints and auto-resizing.
  • Supports: open links, send chat messages (streamed), call tools from the same MCP server, and console logging.
  • Tool pipeline updates: callTool returns mcpUiState; session stores it; ToolCallDiv renders McpAppRenderer when present; added MCPConnection.getResource and mcpMeta plumbing.
  • Current limitations: listing/reading resources and updating model context are not supported yet.

• Dependencies

  • Added @modelcontextprotocol/ext-apps to core and gui.

^{Written for commit ab680d0. Summary will update on new commits.}

[github-actions]

✅ Review Complete

Code Review Summary

⚠️ Continue API authentication failed. Please check your CONTINUE_API_KEY.

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[cubic-dev-ai]

2 issues found across 17 files

Prompt for AI agents (all issues)

Check if these issues are valid — if so, understand the root cause of each and fix them.


<file name="gui/src/pages/gui/ToolCallDiv/MCPAppRenderer.tsx">

<violation number="1" location="gui/src/pages/gui/ToolCallDiv/MCPAppRenderer.tsx:129">
P1: The iframe renders MCP-provided HTML via srcDoc and enables "allow-same-origin" with scripts, which removes the opaque origin normally provided by sandboxing. This lets untrusted MCP HTML run scripts with same-origin access to the parent webview (window.parent/DOM), defeating isolation. Unless same-origin access is strictly required, drop allow-same-origin or gate it to trusted content.</violation>

<violation number="2" location="gui/src/pages/gui/ToolCallDiv/MCPAppRenderer.tsx:223">
P2: Successful tool calls are always marked as errors because `isError` is hardcoded to `true` after the success path.</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}