Add ui/notifications/request-close notification for UI to initiate termination by fredericbarthelet · Pull Request #215 · modelcontextprotocol/ext-apps

fredericbarthelet · 2026-01-08T10:57:25Z

Motivation and Context

Implement bi-directionality on UI termination.
Until now ui/resource-teardown was the only way for Host to initiate UI teardown.
This methods enable UI to initiate its own teardown

Items that might require discussion in this PR:

naming. Similarly to open-link, message, request-display-mode, the name of the request should be action-first/verb-first. Even if we implement a fire and forget pattern (see next point), I would not include notifications in the name. What do you think of ui/close-resource?
should this new ui/close-resource message implements a request/response pattern or a fire and forget type of pattern (where UI fires the event like it would fire a notification without ever expecting an answer). I'm leaning towards fire and forget because the host won't be able to send a response if it proceeds accordingly and does indeed terminates the UI
should we provide a way for the host to refuse terminating the UI or should all ui/close-resource requests be fulfilled? this can be achieved only if we go for a request/response pattern, so I'd not account for this scenario just yet

Types of changes

Bug fix (non-breaking change which fixes an issue)
New feature (non-breaking change which adds functionality)
Breaking change (fix or feature that would cause existing functionality to change)
Documentation update

Checklist

I have read the MCP Documentation
My code follows the repository's style guidelines
New and existing tests pass locally
I have added appropriate error handling
I have added or updated documentation as needed

Additional context

pkg-pr-new · 2026-01-08T10:58:21Z

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commit: ea00acf

fredericbarthelet · 2026-01-08T13:59:00Z

Hey @liady @idosal
Would love to get your feedback on this first shot at ui/close-resource before going further and adding tests and examples.
Let me know what you think (I raised 3 main points in the PR description worth discussion IMHO) :)

fredericbarthelet · 2026-01-14T18:48:51Z

Hey @liady @idosal , sorry for the ping. Just rebased my PR on latest changes from the repo.
Did you got a chance to take a look at the implementation?

Thanks !

liady · 2026-01-14T22:48:42Z

@fredericbarthelet thanks for this! several points:

Can you please also add the spec changes to the PR? We don't want the spec to diverge from the SDK implementation, so it's best to group them in a single PR.
Naming - ui/close-resource makes sense for the current PR purpose. However the next points would show that it might be ui/request-close:
I agree that we shouldn't have a special response if it's ui/close-resource, but why shouldn't we treat it like the UI requesting to be closed? So the host responds with ui/resource-teardown anyway? I saw in the PR that you meant for it to be sent after the UI completed the cleanup process, but what's the reason not to piggyback on the already present ui/resource-teardown>success mechanism?
If we're going with the ui/request-close > ui/resource-teardown mechanism, then concpetually the host decides whether to do it or not.

What do you think?

fredericbarthelet · 2026-01-16T10:50:15Z

Hey @liady, thanks for your comments.

I'll add the spec changes and tests to the PR.
I did not go with piggy-backing on existing ui/resource-teardown implementation, because it felt like the resulting Host/Guest conversation would have been:

Guest: I want to terminate.
Host: Sure, I'll terminate you, please proceed with saving and cleaning up.
Guest: I'm done cleaning up
Host: OK, shutting you down

while, given it was at the guest initiative, it could have been much simpler:

Guest: I'm ready to shut down, please terminate.
Host: OK, shutting you down

For the sake of clarity (and steering away from this conversation analogy 😅), here are the 2 options as sequences.

Option A: ui/close-resource (current PR)

Simpler.
Guest UI is initiating, so it can cleanup before.
UI can freeze while calling this method (should terminate while promise isn't resolved)

sequenceDiagram
participant Host
participant Guest
note right of Guest: App performs cleanup first
Guest->>Guest: saveState(), cleanup()
Guest--)Host: ui/close-resource (request)
note left of Host: Host unmounts immediately
Host->>Host: iframe.remove()

Option B: ui/request-close → ui/resource-teardown

Piggy-back on existing implementation of ui/resource-teardown request which avoids app having to implement shutdown procedure both on host initiated and on guest initiated

sequenceDiagram
participant Host
participant Guest
Guest--)Host: ui/request-close (notification)
note left of Host: Host decides whether to close
alt Host approves close
Host->>Guest: ui/resource-teardown (request)
note right of Guest: App performs cleanup
Guest->>Guest: saveState(), cleanup()
Guest-->>Host: {} (success response)
Host->>Host: iframe.remove()
else Host denies close
note left of Host: Host ignores or defers
end

I can go with option B if you deem it more appropriate here. Let me know :)

fredericbarthelet · 2026-01-23T10:34:57Z

Hey @liady, happy to go with option B if you prefer it this way. Just let me know and I'll update my PR, documentation and add tests accordingly :) Thanks !

idosal · 2026-01-23T10:53:42Z

Thanks @fredericbarthelet, awesome contribution!

View removal may be deferred by the Host or outright blocked, and the view needs to know that it's still running business-as-usual. In that time, data might have mutated (e.g., the user continued to interact with it). That data would now need to be handled gracefully. This leads me down the path of resource-teardown, which would handle this case and spare the app from having to develop two separate mechanisms

liady · 2026-01-23T10:59:43Z

@fredericbarthelet yes, I think for now option B might be preferrable, since it builds on top of the current mechanism, and still leaves the lifecycle control in the hands of the host, preventing possibly surprising edge cases. The view still gains the ability to initiate this process. So I'd recommend implementing B for now.

Do you see a specific use-case in favor of option A - where the view "has" to first initiate its own termination and only then notify the host?

fredericbarthelet · 2026-01-28T17:37:47Z

@liady @idosal ready for review with option B implemented :)
Added test and updated specs as well
e2e tests are failing, but this does not seem to be related to this PR

fredericbarthelet · 2026-02-10T15:22:49Z

Hey @liady @idosal , sorry again for the ping. Wondering if we can consider merging this now that I've updated strategy to piggyback on existing close mechanism?
Thanks for your time and consideration for this PR 🙏

idosal · 2026-02-16T22:45:28Z

Hey @liady @idosal , sorry again for the ping. Wondering if we can consider merging this now that I've updated strategy to piggyback on existing close mechanism? Thanks for your time and consideration for this PR 🙏

Hey @fredericbarthelet, sorry about the delay, completely missed this! Will review tomorrow (hopefully we can merge this ASAP). Thanks for the awesome work 🙏

Copilot

Pull request overview

Adds a new app→host notification that lets a View request its own termination, enabling a bidirectional teardown flow that reuses the existing ui/resource-teardown cleanup mechanism.

Changes:

Introduces ui/notifications/request-close in the spec/types and generated schemas.
Adds App.requestClose() (fire-and-forget) and AppBridge.onrequestclose handler wiring.
Updates documentation and adds an integration test covering request-close → teardown → cleanup.

Reviewed changes

Copilot reviewed 6 out of 9 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/types.ts	Re-exports the new notification type/schema and adds it to `AppNotification`.
src/spec.types.ts	Defines `McpUiRequestCloseNotification` in the protocol spec types.
src/generated/schema.ts	Adds Zod schema for `McpUiRequestCloseNotification`.
src/generated/schema.test.ts	Adds compile-time type/schema inference assertions for the new schema.
src/generated/schema.json	Adds JSON Schema entry for `McpUiRequestCloseNotification`.
src/app.ts	Adds `App.requestClose()` API to emit the notification.
src/app-bridge.ts	Adds `onrequestclose` setter to handle the notification host-side.
src/app-bridge.test.ts	Adds integration test for the close-request initiating teardown flow.
specification/draft/apps.mdx	Documents the new notification and updates lifecycle/cleanup diagram.

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fredericbarthelet · 2026-02-20T14:27:19Z

Hey @idosal, thanks for triggering copilot review on this PR. Implemented feedbacks from its comments.
Let me know if you have any remaining comments before merging :)

fredericbarthelet · 2026-02-24T12:51:22Z

Hey @idosal @liady, sorry for pinging again here. All checks have passed and I've taken into account copilot feedbacks. Any chances this can be merged :)? Thanks for your help on that matter

fredericbarthelet · 2026-03-05T10:24:25Z

Hey @ochafik, any chance this can be merged as is :)? I just rebased on latest main + took into account comments from @idosal and @liady

Thanks for your help on that PR :)

idosal · 2026-03-05T10:34:42Z

Hey @ochafik, any chance this can be merged as is :)? I just rebased on latest main + took into account comments from @idosal and @liady
Thanks for your help on that PR :)

Sorry @fredericbarthelet, missed this in the chaos. I'll close it tonight 🙂

idosal

Thanks @fredericbarthelet ! Sorry it took so long. I left a few comments on the spec. I'd love to hear your thoughts.

fredericbarthelet · 2026-03-17T18:07:42Z

Hey @idosal thanks for your review, I've implemented suggested changes, including renaming to teardown to keep wording consistent across the spec.

Let me know what you think :)

idosal

Thanks @fredericbarthelet ! Looks good. Left a few final thoughts on the spec portion

fredericbarthelet · 2026-03-19T11:22:47Z

Implemented your last comments @idosal and @liady , thanks again for the thorough reviews :)

idosal

Awesome, thanks for the amazing work @fredericbarthelet !

Changes since 1.2.2: - feat: add ui/notifications/request-teardown for view-initiated termination (#215) - feat(pdf-server): annotations, interact tool, page extraction & prompt engineering (#506) - fix(examples): improve mobile support for map, pdf, and threejs examples (#555)

fredericbarthelet force-pushed the add-close-resource branch 4 times, most recently from df4c168 to 52fff75Compare January 8, 2026 13:41

fredericbarthelet marked this pull request as ready for review January 8, 2026 13:57

fredericbarthelet mentioned this pull request Jan 10, 2026
Add support for UI request to close itself alpic-ai/skybridge#279
Closed

fredericbarthelet force-pushed the add-close-resource branch 2 times, most recently from 949f84a to 95bd5ecCompare January 14, 2026 18:47

ochafik added the v2 label Jan 21, 2026

ochafik added this to the v2 milestone Jan 21, 2026

fredericbarthelet force-pushed the add-close-resource branch 5 times, most recently from b844892 to 179843fCompare January 28, 2026 17:32

fredericbarthelet changed the title ~~Add ui/close-resource request for UI to initiate termination~~Add ui/request-close notification for UI to initiate terminationJan 28, 2026

idosal requested a review from Copilot February 17, 2026 17:07

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fredericbarthelet changed the title ~~Add ui/request-close notification for UI to initiate termination~~Add ui/notifications/request-close notification for UI to initiate terminationFeb 20, 2026

fredericbarthelet force-pushed the add-close-resource branch from a2e175e to 289a568Compare February 20, 2026 14:25

fredericbarthelet force-pushed the add-close-resource branch from 289a568 to 9de5a37Compare March 5, 2026 09:57

idosal reviewed Mar 6, 2026
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fredericbarthelet force-pushed the add-close-resource branch 3 times, most recently from c4d7582 to 90cda57Compare March 17, 2026 17:52

idosal reviewed Mar 18, 2026
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Comment threadspecification/draft/apps.mdx Outdated
Comment threadspecification/draft/apps.mdx Outdated

fredericbarthelet added 5 commits March 19, 2026 12:18

Add ui/close-resource request for UI to initiate termination
67e530f

Add missing METHOD export
9e46d05

Fix typo in remaining ui/request-close
57393a2

Align spec terminology to teardown/termination instead of close/clearnup
5102b29

Implement final comments
7c17939

fredericbarthelet force-pushed the add-close-resource branch from 90cda57 to 7c17939Compare March 19, 2026 11:21

idosal reviewed Mar 19, 2026
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Comment threadspecification/draft/apps.mdx Outdated

Removing view behavior on initiation of request termination
ea00acf

fredericbarthelet requested a review from idosal March 19, 2026 19:15

idosal approved these changes Mar 19, 2026
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idosal merged commit c026b39 into modelcontextprotocol:mainMar 19, 2026
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bdstar81 approved these changes Mar 22, 2026
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ochafik mentioned this pull request Mar 23, 2026
chore: bump ext-apps to 1.3.0 #560
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Motivation and Context

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Option A: ui/close-resource (current PR)

Option B: ui/request-close → ui/resource-teardown

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