test(pages): enable complex shallow routing coverage

[james-elicx]

Summary

• wait for the pages-router-complex client-only hydration sentinel before exercising controlled inputs
• enable the shallow routing, router event, and compat-router trial reset tests
• assert the gSSP-derived render timestamp stays stable across the shallow transition
• link the relevant Next.js parity tests and update the documented pass count

All three former fixmes shared one cause on current main: Playwright could change the server-rendered <select> before React attached its onChange handler. The shallow router behavior itself now matches Next.js.

Validation

• vp check tests/e2e/pages-router-complex/client-routing.spec.ts
• negative control: changing the fixture call to { shallow: false } fails on the render timestamp changing
• PLAYWRIGHT_PROJECT=pages-router-complex pnpm exec playwright test tests/e2e/pages-router-complex/client-routing.spec.ts --retries=0 --reporter=line (4 passed)
• PLAYWRIGHT_PROJECT=pages-router-complex pnpm exec playwright test --retries=0 --reporter=line (62 passed, 11 unrelated skipped)

[pkg-pr-new]

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commit: 29c640a

[github-actions]

Example	Preview	Production	Original
app-router-cloudflare	preview	production
pages-router-cloudflare	preview	production
app-router-playground	preview	production	original
realworld-api-rest	preview	production
nextra-docs-template	preview	production
benchmarks	preview	production
hackernews	preview	production	original
workers-cache	preview	production
web	preview	production

[github-actions]

Performance benchmarks

Compared 29c640a against base dc05459 using alternating same-runner rounds. Next.js was unchanged and skipped.

1 improved · 0 regressed · 5 within ±1.5%

Scenario	Framework	Baseline	Current	Change
Client bundle size (gzip)	vinext	134.5 KB	134.5 KB	⚫ 0.0%
Client entry size (gzip)	vinext	122.1 KB	122.1 KB	⚫ 0.0%
Dev server cold start	vinext	2.93 s	2.83 s	🟢 -3.6%
Production build time	vinext	3.18 s	3.16 s	⚫ -0.7%
RSC entry closure size (gzip)	vinext	112.3 KB	112.3 KB	⚫ -0.0%
Server bundle size (gzip)	vinext	189.7 KB	189.7 KB	⚫ -0.0%

View detailed results and traces

_{🟢 improvement · 🔴 regression · ⚫ change below 1.5% · paired base/head}

[james-elicx]

Superseded by #2777. The three client-routing failures were the same Pages dev hydration-order bug: React handlers were not installed before browser load, rather than a separate shallow-router defect. The exact original no-wait cases pass under real Next.js and under #2777, which now carries all six affected no-wait regressions plus the gSSP timestamp assertion from this PR. Keeping this branch for now.