fix: Declare widget csp/prefersBorder on the UI resource, not the tool - #1190
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fix: Declare widget csp/prefersBorder on the UI resource, not the tool#1190jirispilka wants to merge 1 commit into
jirispilka wants to merge 1 commit into
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Per MCP Apps spec (SEP-1865), csp/prefersBorder are UI-resource metadata (McpUiResourceMeta); the tool's _meta.ui (McpUiToolMeta) carries only resourceUri/visibility and types csp/permissions as never. Claude's host warns at runtime about the current placement and ignores the misplaced keys. Split the shared blob into per-surface variants, serve the resource variant on resources/list and resources/read, and add the legacy ui/resourceUri alias that registerAppTool populates for older hosts. Closes #1188 Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
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Why
Closes #1188. Per MCP Apps spec (SEP-1865),
csp/prefersBorderare UI-resource metadata (McpUiResourceMeta) — hosts read them from theresources/readcontent item (with theresources/listentry as fallback) — while the tool's_meta.ui(McpUiToolMeta) carries onlyresourceUri/visibilityand typescsp/permissionsasnever. Claude's host warns at runtime about our current placement and ignores the misplaced keys, so our declared CSP is dead weight on the wrong surface.What changed
Before: one
_meta.uiblob (resourceUri, visibility, csp, prefersBorder) served on every surface — tool descriptor, tool result, resources/list, resources/read.Now:
WidgetConfigcarriesmeta(tool/result:resourceUri,visibility, plus the legacyui/resourceUrialias that the ext-apps SDK'sregisterAppToolpopulates for older hosts) andresourceMeta(list/read:csp,prefersBorder).resource_service.tsservesresourceMetaon both resource surfaces. Widget-meta tests pin the per-surface placement.Notes for reviewers (human-written)
Proof it works
mcpc probe against the built stdio server in apps mode:
tools/listshows widget tools with_meta.ui = {visibility, resourceUri}+ui/resourceUriand nocsp;resources/read ui://widget/search-actors.htmlreturns_metawithopenai/widgetCSP,openai/widgetDomain, andui: {prefersBorder, csp}. Widgets verified rendering in Claude Desktop and MCP Jam alongside #1187 during the ext-apps#696 investigation (this change was bisected there and is behavior-neutral for current hosts — they ignore the misplaced keys either way; this aligns us with the spec surface hosts actually read).🤖 Generated with Claude Code