modelcontextprotocol / modelcontextprotocol/ext-apps
View state persistence
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@idosal is already working on this.
Since Jan 31, 2026.
enhancement
protocol
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Description
Views may need to persist private state locally.
Currently, the protocol doesn't provide a native mechanism for it. Many apps opt for browser API patterns (e.g., localStorage). This solution is brittle because it assumes these APIs are available and consistent across environments, even though their availability depends on unspecified runtime constraints (e.g., user agent, origin management).
MCP Apps should either document the runtime constraints or define a reliable API.
Related to #213
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