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feat(web): honor _meta.ui.domain with a dedicated app origin

Browse source 
An MCP App is rendered by handing its HTML to the sandbox proxy as
`srcdoc`, in a frame sandboxed without `allow-same-origin` — the #1565
isolation model. That gives the app document an opaque origin, so every
request it makes carries `Origin: null` and no CORS / OAuth-callback /
API-key allowlist can admit it. `_meta.ui.domain` is the spec field a
server uses to ask its host for a stable, dedicated origin, and it was
being dropped on the floor.

The field is explicitly host-dependent and the Inspector owns no domain
infrastructure, so it treats any non-empty value as a request rather than
an address, and answers with a real loopback origin on its own listener
(MCP_APP_ORIGIN_PORT, default 6276). One shared origin, path-keyed per
document: that delivers what the field is for without minting a port or
DNS name per app, and is therefore not a per-app isolation boundary.

The inner frame is granted `allow-same-origin` on this path only, which
is what makes the origin real. It is not a #1565 regression: the listener
is on its own port, so the app stays cross-origin to both the proxy and
the Inspector. The proxy refuses the grant if the URL's origin equals its
own, and the grant is never reachable from the server-supplied `sandbox`
string, which is still stripped. The per-app CSP is delivered as a real
response header there rather than only as a <meta>.

Every failure path falls back to the default srcdoc render with a console
warning naming the field, rather than blanking the app.

Also fixes a pre-existing `tsc -b` break on v2/main (useServers.test.tsx
passed `metadata: []` where `RequestMetadata` is expected), which has had
CI red since #2087 and blocks the pre-push gate.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0177mPHAdECD18nLLCTwR5rh
Signed-off-by: cliffhall <cliff@futurescale.com>
This commit is contained in:
cliffhall 2026-08-23 23:03:55 -04:00 • committed by GitHub
commit ec40cf5531
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1 changed files with 1554 additions and 18 deletions
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20
clients/web/src/App.tsx
View file

@ -148,6 +148,7 @@ import {
import { clearScrollMemory } from "./hooks/useScrollMemory";
import type { AppRendererHandle } from "./components/elements/AppRenderer/AppRenderer";
import { createAppBridgeFactory } from "./components/elements/AppRenderer/createAppBridgeFactory";
import { publishAppDocument } from "./lib/publishAppDocument";
import { AppElicitationHost } from "./components/elements/AppElicitation/AppElicitationHost";
import {
AppElicitationController,
@ -808,9 +809,23 @@ function App() {
[],
);
// `_meta.ui.domain` support (#2056): hand a wrapped app document to the
// backend so it can serve it from a dedicated origin, giving the app's
// requests a real `Origin`. Resolves `null` on any backend that can't, and
// the factory then renders the app the default (opaque-origin) way.
const publishDocument = useCallback(
(doc: { html: string; csp?: string }) =>
publishAppDocument(doc, {
baseUrl: configBaseUrl,
authToken: getAuthToken(),
}),
[configBaseUrl],
);
const sandboxBridgeFactory = useMemo(
() =>
createAppBridgeFactory({
publishAppDocument: publishDocument,
getClient: () => inspectorClient?.getAppRendererClient() ?? null,
getListedResourceMeta,
readResource: async (uri) => {
@ -832,7 +847,7 @@ function App() {
});
},
}),
[inspectorClient, getListedResourceMeta],
[inspectorClient, getListedResourceMeta, publishDocument],
);
// App-rendered form elicitations (#1854). The controller is created once and
@ -885,6 +900,7 @@ function App() {
() =>
createAppBridgeFactory({
advertiseElicitation: true,
publishAppDocument: publishDocument,
getClient: () => inspectorClient?.getAppRendererClient() ?? null,
getListedResourceMeta,
readResource: async (uri) => {
@ -903,7 +919,7 @@ function App() {
});
},
}),
[inspectorClient, getListedResourceMeta],
[inspectorClient, getListedResourceMeta, publishDocument],
);
/**
* Close the previous client's session and open one for the client being