fix: preserve experimental capability settings

[victor-openai]

Motivation

Experimental App and Host capability entries are parsed as empty objects, stripping namespaced declarations during ui/initialize. Preserve their keys and settings in both capability maps.

[pkg-pr-new]

Open in StackBlitz

@modelcontextprotocol/ext-apps

npm i https://pkg.pr.new/@modelcontextprotocol/ext-apps@721

@modelcontextprotocol/server-basic-preact

npm i https://pkg.pr.new/@modelcontextprotocol/server-basic-preact@721

@modelcontextprotocol/server-basic-react

npm i https://pkg.pr.new/@modelcontextprotocol/server-basic-react@721

@modelcontextprotocol/server-basic-solid

npm i https://pkg.pr.new/@modelcontextprotocol/server-basic-solid@721

@modelcontextprotocol/server-basic-svelte

npm i https://pkg.pr.new/@modelcontextprotocol/server-basic-svelte@721

@modelcontextprotocol/server-basic-vanillajs

npm i https://pkg.pr.new/@modelcontextprotocol/server-basic-vanillajs@721

@modelcontextprotocol/server-basic-vue

npm i https://pkg.pr.new/@modelcontextprotocol/server-basic-vue@721

@modelcontextprotocol/server-budget-allocator

npm i https://pkg.pr.new/@modelcontextprotocol/server-budget-allocator@721

@modelcontextprotocol/server-cohort-heatmap

npm i https://pkg.pr.new/@modelcontextprotocol/server-cohort-heatmap@721

@modelcontextprotocol/server-customer-segmentation

npm i https://pkg.pr.new/@modelcontextprotocol/server-customer-segmentation@721

@modelcontextprotocol/server-debug

npm i https://pkg.pr.new/@modelcontextprotocol/server-debug@721

@modelcontextprotocol/server-lazy-auth

npm i https://pkg.pr.new/@modelcontextprotocol/server-lazy-auth@721

@modelcontextprotocol/server-map

npm i https://pkg.pr.new/@modelcontextprotocol/server-map@721

@modelcontextprotocol/server-pdf

npm i https://pkg.pr.new/@modelcontextprotocol/server-pdf@721

@modelcontextprotocol/server-scenario-modeler

npm i https://pkg.pr.new/@modelcontextprotocol/server-scenario-modeler@721

@modelcontextprotocol/server-shadertoy

npm i https://pkg.pr.new/@modelcontextprotocol/server-shadertoy@721

@modelcontextprotocol/server-sheet-music

npm i https://pkg.pr.new/@modelcontextprotocol/server-sheet-music@721

@modelcontextprotocol/server-system-monitor

npm i https://pkg.pr.new/@modelcontextprotocol/server-system-monitor@721

@modelcontextprotocol/server-threejs

npm i https://pkg.pr.new/@modelcontextprotocol/server-threejs@721

@modelcontextprotocol/server-transcript

npm i https://pkg.pr.new/@modelcontextprotocol/server-transcript@721

@modelcontextprotocol/server-video-resource

npm i https://pkg.pr.new/@modelcontextprotocol/server-video-resource@721

@modelcontextprotocol/server-wiki-explorer

npm i https://pkg.pr.new/@modelcontextprotocol/server-wiki-explorer@721

commit: b7e9d5b

[Copilot]

Pull request overview

This PR updates the MCP Apps capability schema so experimental capabilities sent during ui/initialize preserve their namespaced keys and associated settings, instead of being parsed into empty objects.

Changes:

• Updated App and Host capability type definitions to model experimental as a keyed map instead of an empty object.
• Regenerated Zod and JSON schemas so experimental is a record (preserving keys/settings) rather than z.object({}) (which strips unknown keys).
• Extended the App ↔ Host initialization integration test to include experimental entries and assert they round-trip correctly.

Reviewed changes

Copilot reviewed 3 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/spec.types.ts	Changes experimental capability typing from {} to a keyed record type for both host and app capabilities.
src/generated/schema.ts	Updates Zod schemas to validate/preserve experimental as a record rather than stripping keys via z.object({}).
src/generated/schema.json	Updates the emitted JSON schema to allow arbitrary additionalProperties for experimental entries instead of rejecting/stripping them.
src/app-bridge.test.ts	Adds coverage ensuring experimental capabilities survive the initialization handshake intact.
specification/draft/apps.mdx	Updates the draft specification examples/types to document the new keyed experimental shape.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[idosal]

Awesome. Thanks @victor-openai !