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fix(mcp): clear backendPromise in onClose to allow backend recreation #40019

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fix(mcp): clear backendPromise in onClose to allow backend recreation #40019

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67ac40d
fix(mcp): clear backendPromise in onClose to allow backend recreation
mlugo-apx Apr 2, 2026
9e5d123
fix(mcp): notify agent when browser connection ended unexpectedly
Apr 2, 2026
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19 changes: 18 additions & 1 deletion packages/playwright-core/src/tools/utils/mcp/server.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -94,8 +94,14 @@ export function createServer(name: string, version: string, factory: ServerBacke
});

let backendPromise: Promise<ServerBackend> | undefined;
let browserConnectionEnded = false;

const onClose = () => backendPromise?.then(b => backendManager.disposeBackend(b)).catch(serverDebug);
const onClose = () => {
const p = backendPromise;
backendPromise = undefined;
browserConnectionEnded = true;
p?.then(b => backendManager.disposeBackend(b)).catch(serverDebug);
};
addServerListener(server, 'close', onClose);

server.setRequestHandler(mcpBundle.CallToolRequestSchema, async (request, extra) => {
Expand All @@ -117,7 +123,10 @@ export function createServer(name: string, version: string, factory: ServerBacke
} : () => {};

try {
let wasRecovery = false;
if (!backendPromise) {
wasRecovery = browserConnectionEnded;
browserConnectionEnded = false;
backendPromise = initializeServer(server, factory, runHeartbeat).catch(e => {
backendPromise = undefined;
throw e;
Expand All @@ -132,6 +141,14 @@ export function createServer(name: string, version: string, factory: ServerBacke
delete toolResult.isClose;
}

// Prepend recovery notice if we reconnected between tool calls
if (wasRecovery) {
toolResult.content = [
{ type: 'text', text: '**Note:** Browser connection ended unexpectedly. A new browser has been started — previous state might be lost.' },
...toolResult.content,
];
}

const mergedResult = mergeTextParts(toolResult);
serverDebugResponse('callResult', mergedResult);
return mergedResult;
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