Internal locator('body') strict-mode check crashes every tool call on pages with malformed nested <body> markup #42100

Environment

• playwright-mcp 0.0.78 (also reproduced on @playwright/mcp@latest via npx, and a
  second unrelated MCP server wrapping the same core)
• macOS 25.5.0 (Darwin), arm64
• Node v26.5.0
• Reproduced with --isolated, --caps vision, and --snapshot-mode none — none of
  these flags change the behavior

Summary
Every tool call except browser_navigate fails with:

Error: strict mode violation: locator('body') resolved to 2 elements:
    1) <body>…</body> aka locator('body').first()
    2) <body>…</body> aka locator('body').nth(1)

on any page whose HTML has more than one element in the DOM (in our case,
a real-world SaaS app with invalid nested ... markup
in its page template — confirmed via a standalone Playwright script, independent
of playwright-mcp, that document.querySelectorAll('body') returns 2 connected
nodes on the affected page).

browser_navigate always succeeds (even navigating onto the affected page). Every
other tool (browser_take_screenshot, browser_close, browser_run_code_unsafe,
click, etc.) fails identically once that page is loaded, because whatever internal
readiness/snapshot check runs on each tool call resolves body via an implicit
strict-mode locator.

Ruled out during investigation

• Stale install / version mismatch (npx cache, npm latest, Homebrew all pinned
  to 0.0.78)
• Specific MCP server implementation (reproduced identically on two independent
  playwright-mcp-based servers)
• Browser extensions (isolated automation profile launches Chrome with
  --disable-extensions explicitly; bug persists)
• Stale profile/process state (cleared all profiles, used a fresh --isolated
  in-memory profile; bug persists)
• Interaction mode (--caps vision uses coordinate-based tools instead of the
  accessibility tree; bug persists)
• Response snapshot generation (--snapshot-mode none disables the AI-facing
  snapshot entirely; bug persists — confirming the body-locator check is part
  of core tool/action handling, not the optional snapshot feature)

Repro (works on other sites)

• https://www.google.com — all tools work normally
• https://www.yahoo.com — all tools work normally (despite 190+ console errors
  and many third-party ad iframes)
• Affected page — every non-navigate tool call fails identically, every time

Suggested fix
Scope the internal body-resolution locator to .first() (matching the browser's
own document.body semantics) or catch the strict-mode violation and degrade
gracefully, rather than failing the entire tool call. A malformed page shouldn't
be able to make every tool call unusable.