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

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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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15
clients/web/server/server.ts
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@ -16,6 +16,10 @@ import type { Context } from "hono";
import { createRemoteApp } from "../../../core/mcp/remote/node/server.ts";
import { formatHostForUrl } from "../../../core/node/hostUrl.ts";
import { createSandboxController } from "./sandbox-controller.js";
import {
createAppOriginController,
sandboxOriginList,
} from "./app-origin-controller.js";
import { injectAuthToken } from "./inject-auth-token.js";
import type { WebServerConfig } from "./web-server-config.js";
import { getSecretStorageInfo } from "../../../core/auth/node/secret-store-selection.ts";
@ -44,6 +48,15 @@ export async function startHonoServer(
allowedOrigins: config.allowedOrigins,
});
await sandboxController.start();
// The dedicated origin apps declaring `_meta.ui.domain` are served from
// (#2056). Started after the sandbox because its `frame-ancestors` names the
// sandbox proxy's origin — the proxy is what embeds the app frame.
const appOriginController = createAppOriginController({
port: config.appOriginPort,
host: config.sandboxHost,
embedderOrigins: sandboxOriginList(sandboxController.getUrl()),
});
await appOriginController.start();
const resolvedAuthToken =
config.authToken ||
@ -65,6 +78,7 @@ export async function startHonoServer(
initialServers: config.initialServers ?? undefined,
allowedOrigins: config.allowedOrigins,
sandboxUrl: sandboxController.getUrl() ?? undefined,
publishAppDocument: (doc) => appOriginController.publish(doc),
logger: config.logger,
initialConfig: webServerConfigToInitialPayload(config, secretStorage),
// The startup value above is what the banner printed; the route
@ -159,6 +173,7 @@ export async function startHonoServer(
async close(): Promise<void> {
await closeApi();
await sandboxController.close();
await appOriginController.close();
if ("closeAllConnections" in httpServer) {
httpServer.closeAllConnections();
}