[MCP]: browser_close caches a disposed backend with shared HTTP clients #42363

Using @playwright/[email protected] with HTTP transport and --shared-browser-context:

1. Clients A and B each call a browser tool.
2. A calls browser_close.
3. A calls browser_tabs { action: "new", url: "https://example.com" }.

A then fails until restart with:

TypeError: Cannot read properties of undefined
(reading 'checkUrlAndNavigate' / 'waitForInitialized')

browser_close disposes A's Context, but its cached backendPromise is cleared only on disconnected. Because B keeps the shared browser alive, no disconnect occurs and A reuses the disposed backend.

Expected: explicit close invalidates A's cached backend so the next call creates a fresh one.

This appears to be a 0.0.79 regression. Please clear backendPromise on explicit close and add a two-client regression test.

Version: @playwright/mcp 0.0.79, playwright-core 1.63.0-alpha-2026-08-05.