MCP Apps: align with the 2026-01-26 stable spec - #2573
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SamMorrowDrums merged 4 commits intoMay 29, 2026
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Placeholder commit to open a draft PR. See plan in session workspace. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Per the MCP Apps 2026-01-26 spec, servers SHOULD check client capabilities before advertising UI-enabled tools. Extend the inventory strip gate to remove _meta.ui not only when the feature flag is off, but also when the request context explicitly reports the client lacks UI support (HasUISupport returns supported=false, ok=true). When the capability is unknown (ok=false, e.g. stdio paths), fall through to the existing feature-flag gate so existing behaviour is preserved. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
* Explicitly set prefersBorder on every UI resource — false for the get_me profile card, true for the issue/PR write forms — since hosts' defaults vary. * Declare an empty csp on issue_write_ui and pr_write_ui to document that they need no external origins. * Point spec link comment at the stable 2026-01-26 location. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
* Declare appCapabilities.availableDisplayModes (defaults to ["inline"]) during initialization, as required by the new spec. * Track McpUiHostContext (and its updates via onhostcontextchanged) and thread it into AppProvider, which now picks up host-supplied theme + CSS style variables and projects them onto the root element so Primer components inherit host theming. * Add setModelContext and openLink helpers to useMcpApp. issue-write and pr-write call setModelContext on a successful submission so the agent has the new entity in its next-turn context; get-me uses openLink for the profile's external blog link. The pinned @modelcontextprotocol/ext-apps ^1.7.2 was already resolved to 1.7.2 in the lockfile, so no dependency bump is required for the new HostContext / openLink / updateModelContext APIs. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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May 29, 2026 15:32
mattdholloway
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May 29, 2026 15:37
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Pull request overview
This PR aligns the MCP Apps implementation with the stable 2026-01-26 spec across server-side tool metadata handling, UI resource metadata, and React app host integration.
Changes:
- Adds client UI-capability-aware stripping of MCP Apps _meta.ui during tool registration.
- Updates UI resource metadata with explicit prefersBorder, CSP metadata, and stable spec references.
- Updates React views to declare display modes, consume host context/theme variables, open links through the host, and update model context after write actions.
| File | Description |
|---|---|
| pkg/inventory/registry.go | Centralizes _meta.ui strip logic using feature flag and UI capability context. |
| pkg/inventory/registry_test.go | Adds truth-table coverage for the new strip predicate. |
| pkg/http/handler_test.go | Verifies UI metadata is stripped/preserved based on client UI capability context. |
| pkg/github/ui_resources.go | Adds stable-spec UI resource metadata for CSP and border preference. |
| ui/src/hooks/useMcpApp.ts | Adds display mode capabilities, host context tracking, model context updates, and host link opening. |
| ui/src/components/AppProvider.tsx | Applies host theme and CSS variables to Primer rendering. |
| ui/src/apps/get-me/App.tsx | Threads host context and routes blog links through ui/open-link. |
| ui/src/apps/issue-write/App.tsx | Threads host context and updates model context after issue create/update. |
| ui/src/apps/pr-write/App.tsx | Threads host context and updates model context after PR creation. |
Copilot's findings
- Files reviewed: 9/9 changed files
- Comments generated: 0
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SamMorrowDrums
approved these changes
May 29, 2026
This was referenced Jun 9, 2026
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Aligns this repository's MCP Apps implementation with the stable 2026-01-26 spec (https://github.com/modelcontextprotocol/ext-apps/blob/main/specification/2026-01-26/apps.mdx).
Server (Go)
Views (React, ui/)
Testing
Companion PR on github-mcp-server-remote: https://github.com/github/github-mcp-server-remote/pull/849