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test(mcp): work around Chromium losing WebMCP tools in same-origin iframes #42888

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Merged
Dmitry Gozman (dgozman) merged 1 commit into from
Sep 24, 2026
Merged

test(mcp): work around Chromium losing WebMCP tools in same-origin iframes #42888

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12 changes: 9 additions & 3 deletions tests/mcp/cli-webmcp.spec.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -49,6 +49,12 @@ function serveMain(server: any, body: string) {
});
}

// Reloading the frame once replaces the initial blank page's window in Chromium
// and works around the bug where tools do not register.
function iframe(src: string) {
return `<iframe src="${src}" onload="if (!this.dataset.reloaded) { this.dataset.reloaded = '1'; this.contentWindow.location.reload(); }"></iframe>`;
}

test('webmcp-list and webmcp-call', async ({ cli, server, mcpBrowser }, testInfo) => {
await writeWebMCPConfig(mcpBrowser, testInfo);
serveMain(server, `<script>
Expand Down Expand Up @@ -136,7 +142,7 @@ test('webmcp-list stitches tools across frames', async ({ cli, server, mcpBrowse
test.skip(mcpBrowser === 'firefox', 'Firefox does not support registering WebMCP tools in iframes yet, https://bugzilla.mozilla.org/show_bug.cgi?id=2019743');
await writeWebMCPConfig(mcpBrowser, testInfo);

serveMain(server, `<script>${kRegisterAdd}</script><iframe src="/frame.html"></iframe>`);
serveMain(server, `<script>${kRegisterAdd}</script>${iframe('/frame.html')}`);
server.setRoute('/frame.html', (req: any, res: any) => {
res.writeHead(200, { 'Content-Type': 'text/html' });
res.end(`<script>
Expand Down Expand Up @@ -171,7 +177,7 @@ test('webmcp-call disambiguates duplicate tool names by frame', async ({ cli, se
async execute() { return { content: [{ type: 'text', text: '${text}' }] }; },
});
`;
serveMain(server, `<script>${registerEcho('main')}</script><iframe src="/frame.html"></iframe>`);
serveMain(server, `<script>${registerEcho('main')}</script>${iframe('/frame.html')}`);
server.setRoute('/frame.html', (req: any, res: any) => {
res.writeHead(200, { 'Content-Type': 'text/html' });
res.end(`<script>${registerEcho('frame')}</script>`);
Expand All @@ -191,7 +197,7 @@ test('webmcp-call disambiguates same-name tools in identical same-origin frames'

// Two iframes of the very same URL each own a tool called "echo", so the frame URL alone
// cannot address them and the listing falls back to the frame position.
serveMain(server, `<iframe src="/widget.html"></iframe><iframe src="/widget.html"></iframe>`);
serveMain(server, `${iframe('/widget.html')}${iframe('/widget.html')}`);
server.setRoute('/widget.html', (req: any, res: any) => {
res.writeHead(200, { 'Content-Type': 'text/html' });
res.end(`<script>
Expand Down
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