fix(dev): initialize App instrumentation in the RSC runner

[lyzno1]

Fixes #3361.

Node App Router dev loads instrumentation through the Pages SSR runner, rejecting dynamic server-only imports and initializing different module instances from App requests. Reuse the existing RSC runner so registration uses React server conditions and shares initialized module state with request handling. Pages-only startup keeps its direct runner; external runtimes initialize through their own entries.

Alternative to #3362 for the Node dev regression, without widening the server-only allowlist. Matches Next.js's server-layer instrumentation test and initialization ordering.

Regression tests cover static/dynamic imports, React conditions, module state, async ordering, concurrent registration, Pages-first hybrid requests, failed registration, and rejection of a Client Component importing the same server-only dependency. A Playwright E2E in the existing non-Cloudflare app-with-src fixture opens the affected page and verifies that instrumentation initialized the same server-only module instance used by the App request.

Validation:

• Controlled E2E red/green: main fails with the reported 'server-only' cannot be imported in client build ('ssr' environment) chain and the PR head passes.
• PLAYWRIGHT_PROJECT=app-with-src vp exec playwright test --project=app-with-src (4 passed)
• vp test run tests/instrumentation-dev.test.ts tests/instrumentation.test.ts (50 passed)
• Focused App production module-identity test (1 passed)
• vp check
• vp run vinext#build
• node scripts/ci-integration-shard.mjs --check --shard-total=10

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@vinext/cloudflare

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create-vinext-app

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@vinext/types

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vinext

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@cloudflare/workers-response-store

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commit: 41f9bd8

[github-actions]

Performance benchmarks

Compared 41f9bd8 against base 3898ef2 using alternating same-runner rounds. Next.js was unchanged and skipped.

0 improved · 0 regressed · 6 within ±1.5%

Scenario	Framework	Baseline	Current	Change
Client bundle size (gzip)	vinext	142.3 KB	142.3 KB	⚫ +0.0%
Client entry size (gzip)	vinext	129.7 KB	129.7 KB	⚫ +0.0%
Dev server cold start	vinext	3.51 s	3.48 s	⚫ -0.8%
Production build time	vinext	3.96 s	4.00 s	⚫ +1.0%
RSC entry closure size (gzip)	vinext	127.5 KB	127.6 KB	⚫ +0.0%
Server bundle size (gzip)	vinext	225.6 KB	225.7 KB	⚫ +0.0%

View detailed results and traces

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

[james-elicx]

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[james-elicx]

/bigbonk review for issues

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Posted 1 actionable inline finding. Targeted instrumentation tests pass.

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[james-elicx]

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LGTM!

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