fix: adjust ui/message content to be ContentBlock[]#166
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RomKadria
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Dec 18, 2025
aharvard
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Jan 16, 2026
The MCP Apps draft spec (SEP-1865) has been in flux regarding the
ui/message params.content type. After discussion with the spec authors,
the agreed format is ContentBlock[] (array of content blocks) rather
than a single ContentBlock object.
This change:
- Updates McpMethodParams['ui/message'] to expect content as ContentBlock[]
- Adds ContentBlock type supporting text, image, and resource blocks
- Updates the handler to extract text from the first text block in the array
- Returns empty object {} on success per the spec
Related spec discussions:
- modelcontextprotocol/ext-apps#48
- modelcontextprotocol/ext-apps#119
- MCP-UI-Org/mcp-ui#166
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fixed in #167 |
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This PR fixes the type of
ui/messagecontent from MCP Apps bridge to beContentBlock[](see discussion here )There are lint fixes here (since we moved to eslint@9).
The actual content block fixes are two lines in
adapter-runtime.js: https://github.com/MCP-UI-Org/mcp-ui/pull/166/changes#diff-dfbf3818886f740fd71a692dd96cf29550a2ff6c98b62670d7edf302f9bd608fL536-R578