Migrate MCP Apps support from insiders mode to feature flag with insiders opt-in by mattdholloway · Pull Request #2282 · github/github-mcp-server

mattdholloway · 2026-04-02T12:27:08Z

Summary

This pull request transitions MCP Apps from an insiders-only experimental feature to a general feature flag (remote_mcp_ui_apps) that can be enabled independently.

Why

Closes https://github.com/github/copilot-mcp-core/issues/1471

What changed

MCP Apps feature flag transition and enablement:

MCP Apps is now controlled by the remote_mcp_ui_apps feature flag, not by insiders mode. Insiders mode still enables the flag for backward compatibility. (docs/insiders-features.md, docs/server-configuration.md, [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
Inventory builder now uses a dedicated WithMCPApps method to control UI metadata, and MCP Apps UI metadata is only included if the feature flag is enabled. (pkg/inventory/builder.go, [1] [2] [3] [4]

HTTP and server-side feature flag handling:

Adds support for feature flags in HTTP headers (X-MCP-Features), with a whitelist for allowed flags (currently only remote_mcp_ui_apps). Insiders mode implies the MCP Apps feature flag for compatibility. (pkg/http/server.go, [1] [2] [3]
Server and handler logic updated to check for the MCP Apps feature flag (either from headers or insiders mode) and enable UI features accordingly. (pkg/http/handler.go, [1] [2]

Tool handler and test updates:

Tool handlers for issue_write and create_pull_request now check the MCP Apps feature flag instead of insiders mode to determine UI behavior. (pkg/github/issues.go, [1] pkg/github/pullrequests.go, [2]
Associated tests are renamed and updated to check the new feature flag logic. (pkg/github/issues_test.go, [1] [2] [3]; pkg/github/pullrequests_test.go, [4] [5]

MCP impact

No tool or API changes
Tool schema or behavior changed
New tool added

Prompts tested (tool changes only)

Security / limits

No security or limits impact
Auth / permissions considered
Data exposure, filtering, or token/size limits considered

Tool renaming

I am renaming tools as part of this PR (e.g. a part of a consolidation effort)
- I have added the new tool aliases in deprecated_tool_aliases.go
I am not renaming tools as part of this PR

Note: if you're renaming tools, you must add the tool aliases. For more information on how to do so, please refer to the official docs.

Lint & tests

Linted locally with ./script/lint
Tested locally with ./script/test

Docs

Not needed
Updated (README / docs / examples)

…ders opt-in

Copilot

Pull request overview

This PR migrates MCP Apps (interactive UI forms) enablement from “insiders mode” to an explicit feature flag (remote_mcp_ui_apps), while keeping backward compatibility by treating insiders mode as implying the flag.

Changes:

Introduces github.MCPAppsFeatureFlag (remote_mcp_ui_apps) and wires it through stdio/HTTP feature checking with an insiders-mode transitional fallback.
Adds inventory builder support (WithMCPApps) to strip/keep MCP Apps UI metadata (Meta["ui"]) based on the feature flag.
Updates tool behavior gates and documentation to reference the feature flag instead of insiders mode.

Reviewed changes

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

Show a summary per file

File	Description
pkg/inventory/registry_test.go	Renames/extends tests for MCP Apps gating and meta stripping; adds `stripMetaKeys` coverage.
pkg/inventory/builder.go	Adds `WithMCPApps`, separates insiders stripping from MCP Apps UI metadata stripping, and introduces `stripMetaKeys`.
pkg/http/server.go	Whitelists `remote_mcp_ui_apps` for `X-MCP-Features` and adds transitional insiders behavior in feature checker.
pkg/http/handler.go	Applies `WithInsidersMode` and `WithMCPApps` to the inventory builder based on request context/header features.
pkg/github/pullrequests.go	Gates PR UI form behavior on `remote_mcp_ui_apps` feature flag instead of insiders mode.
pkg/github/pullrequests_test.go	Updates UI-gate test setup to use feature checker-based deps rather than `InsidersMode`.
pkg/github/issues.go	Gates issue UI form behavior on `remote_mcp_ui_apps` feature flag instead of insiders mode.
pkg/github/issues_test.go	Updates UI-gate test setup to use feature checker-based deps rather than `InsidersMode`.
pkg/github/feature_flags.go	Adds the exported `MCPAppsFeatureFlag` constant.
internal/ghmcp/server.go	Ensures stdio “insiders mode” also enables `remote_mcp_ui_apps`; registers UI resources based on the flag.
docs/server-configuration.md	Documents feature flags and MCP Apps configuration via `X-MCP-Features` / `--features`.
docs/insiders-features.md	Removes MCP Apps from insiders-only list; points to feature-flag configuration.

pkg/inventory/builder.go

pkg/inventory/registry_test.go

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

bdweb771-art

@codex[agent]

Copilot

Pull request overview

This PR migrates MCP Apps enablement from being tied to insiders mode to a dedicated feature flag (remote_mcp_ui_apps), while preserving backward compatibility by having insiders mode imply the feature flag.

Changes:

Introduces github.MCPAppsFeatureFlag and updates tool handlers (issue_write, create_pull_request) to gate MCP Apps UI behavior via feature flag checks.
Adds transport-specific feature enablement: HTTP via X-MCP-Features (whitelisted) and stdio via --features, with insiders-mode implication during the transition.
Updates inventory building to strip ui metadata unless MCP Apps is enabled, and refreshes related tests and docs.

Show a summary per file

File	Description
pkg/github/feature_flags.go	Defines the `remote_mcp_ui_apps` feature flag constant and documents its purpose.
pkg/github/issues.go	Switches UI-gate logic from insiders mode to the MCP Apps feature flag.
pkg/github/issues_test.go	Updates UI-gate tests to use feature checker-based enablement instead of insiders mode.
pkg/github/pullrequests.go	Switches UI-gate logic from insiders mode to the MCP Apps feature flag.
pkg/github/pullrequests_test.go	Updates UI-gate tests to use feature checker-based enablement instead of insiders mode.
pkg/http/server.go	Whitelists `remote_mcp_ui_apps` for `X-MCP-Features` and adds insiders→flag transitional behavior in the HTTP feature checker.
pkg/http/handler.go	Enables MCP Apps inventory behavior based on `X-MCP-Features` or insiders mode (transitional).
pkg/inventory/builder.go	Adds `WithMCPApps` and strips `ui` metadata by default unless MCP Apps is enabled; generalizes meta stripping via `stripMetaKeys`.
pkg/inventory/registry_test.go	Renames/adds tests around MCP Apps meta stripping and `stripMetaKeys`.
internal/ghmcp/server.go	Ensures stdio mode treats insiders as implying the feature flag and registers UI resources only when the flag is enabled.
docs/server-configuration.md	Documents feature flags and adds MCP Apps configuration examples using `X-MCP-Features` / `--features`.
docs/insiders-features.md	Removes MCP Apps from insiders-only docs and notes there are currently no insiders-only features.

Copilot's findings

Comments suppressed due to low confidence (1)

pkg/inventory/registry_test.go:2142

This test uses require.Nil(result.Tool.Meta["ui"]) (and similar) to assert key stripping, but a map lookup returns nil both when the key is missing and when the key exists with a nil value. To ensure stripMetaKeys actually removes the keys, assert map membership (_, ok := meta["ui"]) rather than only the value.

	require.Nil(t, result.Tool.Meta["ui"], "ui should be stripped")
	require.Nil(t, result.Tool.Meta["experimental_feature"], "experimental_feature should be stripped")
	require.Nil(t, result.Tool.Meta["beta"], "beta should be stripped")
	require.Equal(t, "kept", result.Tool.Meta["description"], "description should be preserved")

Files reviewed: 12/12 changed files
Comments generated: 2

pkg/inventory/registry_test.go

pkg/inventory/builder.go

SamMorrowDrums · 2026-04-07T13:11:28Z

docs/server-configuration.md

+Insiders Mode unlocks experimental features. We created this mode to have a way to roll out experimental features and collect feedback. So if you are using Insiders, please don't hesitate to share your feedback with us! Features in Insiders Mode may change, evolve, or be removed based on user feedback.
+
+> [!NOTE]
+> Insiders mode also enables the `remote_mcp_ui_apps` feature flag for backward compatibility. See [MCP Apps](#mcp-apps) below.


Just a flag that this is brittle docs that would need manual update when no longer true.

SamMorrowDrums

Generally happy with this, but it might be nice to avoid the complexity of insiders only and just use feature flags for everything. Insiders would just auto enable a list of feature flags, and all changes would propagate as a consequence.

SamMorrowDrums · 2026-04-07T13:14:35Z

pkg/http/server.go

 		if knownSet[flag] && slices.Contains(ghcontext.GetHeaderFeatures(ctx), flag) {
 			return true, nil
 		}
+		// Transitional: insiders mode implies remote_mcp_ui_apps feature flag


I'll be honest, I always expected that we would go the other direction here, and all stuff would be a feature flag, and a selection of flags would be available on insiders mode, rather than insiders mode enabling stuff for which there is no feature flag.

Does that make sense? I personally still feel like that. Insiders mode should (where possible), just be a view on a list of feature flags.

SamMorrowDrums · 2026-04-07T13:16:11Z

pkg/inventory/builder.go

 // WithInsidersMode enables or disables insiders mode features.
-// When insiders mode is disabled (default), UI metadata is removed from tools
-// so clients won't attempt to load UI resources.
+// When insiders mode is disabled (default), tools marked InsidersOnly are removed


If we do the feature flag list thing, then we don't need the extra complexity here, of transitional stuff. My vote is to remove this, and to just have features that are load bearing for insiders.

SamMorrowDrums · 2026-04-07T13:16:47Z

pkg/inventory/builder.go

 }

+// WithMCPApps enables or disables MCP Apps UI features.
+// When disabled (default), the "ui" Meta key is stripped from tools


This can also be done via feature flag.

migrate mcp apps support from insiders mode to feature flag with insi…

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…ders opt-in

mattdholloway requested a review from a team as a code owner April 2, 2026 12:27

Copilot AI review requested due to automatic review settings April 2, 2026 12:27

mattdholloway changed the title ~~Migrate mcp apps support from insiders mode to feature flag with insiders opt-in~~ Migrate MCP Apps support from insiders mode to feature flag with insiders opt-in Apr 2, 2026

Copilot started reviewing on behalf of mattdholloway April 2, 2026 12:27 View session

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Update pkg/inventory/registry_test.go

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Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

ahamedjobayer081-spec approved these changes Apr 3, 2026

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bdweb771-art approved these changes Apr 4, 2026

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mattdholloway and others added 2 commits April 7, 2026 09:10

Merge branch 'main' into matt/mcp-apps-feature-flag

c74f6c5

refactor: improve key existence check in stripMetaKeys function

7830fe6

mattdholloway requested a review from Copilot April 7, 2026 11:38

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Migrate MCP Apps support from insiders mode to feature flag with insiders opt-in#2282

Migrate MCP Apps support from insiders mode to feature flag with insiders opt-in#2282
mattdholloway wants to merge 4 commits intomainfrom
matt/mcp-apps-feature-flag

mattdholloway commented Apr 2, 2026 •

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Summary

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Tool renaming

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mattdholloway commented Apr 2, 2026 •

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