feat: support experimental messages by idosal · Pull Request #176 · MCP-UI-Org/mcp-ui

idosal · 2026-02-06T16:19:36Z

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Copilot

Pull request overview

Adds an “experimental messages” path to MCP Apps by letting guest UIs send arbitrary JSON-RPC methods to the host, handled via a new onFallbackRequest hook on AppRenderer, plus documentation restructuring to emphasize AppRenderer over legacy renderers.

Changes:

Add sendExperimentalRequest() helper in @mcp-ui/server to send JSON-RPC requests from guest iframe → host via postMessage.
Add onFallbackRequest support in AppRenderer (and tests) by wiring AppBridge.fallbackRequestHandler.
Update docs/navigation to add an AppRenderer reference page and mark legacy UIResourceRenderer docs as deprecated.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
sdks/typescript/server/src/index.ts	Adds `sendExperimentalRequest()` experimental JSON-RPC helper for guest iframes.
sdks/typescript/client/src/index.ts	Re-exports `JSONRPCRequest` type for host handler typing.
sdks/typescript/client/src/components/AppRenderer.tsx	Introduces `onFallbackRequest` prop and registers `fallbackRequestHandler` on `AppBridge`.
sdks/typescript/client/src/components/tests/AppRenderer.test.tsx	Adds coverage for `onFallbackRequest` registration, invocation, and error behavior.
docs/src/guide/mcp-apps.md	Documents `onFallbackRequest` and the guest-side `sendExperimentalRequest()` flow.
docs/src/guide/client/wc-usage-examples.md	Marks WC docs as legacy/deprecated and points to `AppRenderer`.
docs/src/guide/client/walkthrough.md	Updates “Next steps” links to the new `AppRenderer` doc.
docs/src/guide/client/resource-renderer.md	Marks `UIResourceRenderer` as deprecated/legacy.
docs/src/guide/client/react-usage-examples.md	Marks React `UIResourceRenderer` docs as legacy/deprecated.
docs/src/guide/client/overview.md	Adds `AppRenderer` as the recommended renderer in navigation.
docs/src/guide/client/app-renderer.md	New `AppRenderer` reference page including `onFallbackRequest` documentation.
docs/src/.vitepress/config.ts	Updates sidebar to include `AppRenderer` and group legacy docs.

sdks/typescript/server/src/index.ts

sdks/typescript/client/src/components/AppRenderer.tsx

sdks/typescript/client/src/components/__tests__/AppRenderer.test.tsx

aharvard · 2026-02-11T16:45:43Z

hey @idosal @liady TSYM for working in onFallbackRequest!

We're about to merge AppRenderer in goose. Do you have an ETA on when we can start playing around with thie new prop?

++ @alexhancock and linking to block/goose#7039 (our plan is to rebase that onto AppRenderer soon)

aharvard

awesome!

idosal · 2026-02-12T01:20:46Z

@copilot open a new pull request to apply changes based on the comments in this thread

Copilot · 2026-02-12T01:20:54Z

@idosal I've opened a new pull request, #181, to work on those changes. Once the pull request is ready, I'll request review from you.

idosal · 2026-02-12T01:21:36Z

hey @idosal @liady TSYM for working in onFallbackRequest!

We're about to merge AppRenderer in goose. Do you have an ETA on when we can start playing around with thie new prop?

++ @alexhancock and linking to block/goose#7039 (our plan is to rebase that onto AppRenderer soon)

Thanks for the heads up @aharvard! Today/tomorrow

alexhancock · 2026-02-12T18:07:04Z

Nice! Would love to see this one go in so I can update/rebase and get block/goose#7039 going

Copilot

Pull request overview

Copilot reviewed 12 out of 12 changed files in this pull request and generated 5 comments.

sdks/typescript/server/src/index.ts

sdks/typescript/client/src/components/AppRenderer.tsx

Co-authored-by: Copilot <[email protected]>

Copilot

Pull request overview

Copilot reviewed 12 out of 12 changed files in this pull request and generated 2 comments.

sdks/typescript/server/src/index.ts

…6.1.0) (2026-02-13) ### Features * support experimental messages ([#176](#176)) ([327e4d9](327e4d9))

github-actions · 2026-02-13T00:55:59Z

🎉 This PR is included in version 6.1.0 🎉

The release is available on:

Your semantic-release bot 📦🚀

…6.1.0) (2026-02-13) ### Features * support experimental messages ([#176](#176)) ([327e4d9](327e4d9))

github-actions · 2026-02-13T00:56:51Z

🎉 This PR is included in version 6.1.0 🎉

The release is available on:

Your semantic-release bot 📦🚀

feat: support experimental messages

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Copilot AI review requested due to automatic review settings February 6, 2026 16:19

Copilot started reviewing on behalf of idosal February 6, 2026 16:19 View session

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aharvard mentioned this pull request Feb 6, 2026

feat(apps): Integrate AppRenderer from @mcp-ui/client SDK block/goose#7013

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aharvard approved these changes Feb 11, 2026

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Copilot AI mentioned this pull request Feb 12, 2026

Address security and type safety issues in experimental messages implementation #181

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idosal requested a review from Copilot February 12, 2026 22:53

Copilot started reviewing on behalf of idosal February 12, 2026 22:54 View session

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idosal and others added 2 commits February 13, 2026 01:01

Update sdks/typescript/client/src/components/AppRenderer.tsx

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Co-authored-by: Copilot <[email protected]>

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idosal requested a review from Copilot February 12, 2026 23:06

Copilot started reviewing on behalf of idosal February 12, 2026 23:06 View session

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add tests

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idosal merged commit 327e4d9 into main Feb 13, 2026
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github-actions bot pushed a commit that referenced this pull request Feb 13, 2026

chore(release): 6.1.0 [skip ci]\n\n# [6.1.0](client/v6.0.0...client/v…

3cc0027

…6.1.0) (2026-02-13) ### Features * support experimental messages ([#176](#176)) ([327e4d9](327e4d9))

github-actions bot added the released label Feb 13, 2026

github-actions bot pushed a commit that referenced this pull request Feb 13, 2026

chore(release): 6.1.0 [skip ci]\n\n# [6.1.0](server/v6.0.1...server/v…

26a4821

…6.1.0) (2026-02-13) ### Features * support experimental messages ([#176](#176)) ([327e4d9](327e4d9))

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