test: deflake basePath external navigation (#97611)
## Summary
The basePath external-navigation test depended on loading Google and
recognizing its DOM before exercising browser history. That made the
test sensitive to public network availability and third-party page
changes; the reported failure was confirmed in the Safari/WebKit CI run
on the initial attempt and both retries.
For local and CI test-server runs, this replaces the public dependency
with a minimal page served from a separate local origin, preserving the
cross-origin, full-document navigation being tested. Deploy mode remains
enabled and uses a deploy-accessible external target because deployed
browsers cannot reach the test runner. Both paths now synchronize on
browser origin and exact restored-page state instead of third-party DOM
or a fixed sleep.
## Verification
- Focused production/start-mode test passed three consecutive times in
Firefox
- Focused production/start-mode test passed in Chromium
- Prettier and ESLint passed for the changed files
- `pnpm build-all`
- Not run: Safari/WebKit locally (Playwright’s unsupported Amazon Linux
fallback requires incompatible Ubuntu system libraries; the Safari CI
job is the definitive validation)
- Not run: deploy-mode execution locally (deployment credentials
unavailable; the deploy path remains enabled for CI)
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Co-authored-by: vercel-fleet-prod[bot] <318278635+vercel-fleet-prod[bot]@users.noreply.github.com>
Co-authored-by: Tobias Koppers <1365881+sokra@users.noreply.github.com>
