fix: use static replacement for websocket feature

[pi0]

We use static flags from a virtual import + optimization.inlineConst + minify: dce-only to enable rolldown / rolldown-vite to tree-shake unused logic.

However it seems not effective on entrypoints where we conditionally import crossws for opt-in websocket feature (/cc @sapphi-red it is reprodicable with both rolldown and vite8 with any nitro nightly before this)

This PR worksaround issue by using a replacement via import.meta..

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Project	Deployment	Review	Updated (UTC)
nitro.build	Ready	Preview, Comment	Jan 21, 2026 6:24pm

[coderabbitai]

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📝 Walkthrough

Walkthrough

Refactors WebSocket feature detection from compile-time feature flags to runtime metadata injection. Removes the hasWebSocket generated flag constant and replaces all occurrences with import.meta._websocket, injected via build config and exposed through the NitroImportMeta interface.

Changes

Cohort / File(s)	Summary
Build configuration and types src/build/config.ts, src/types/global.ts	Adds _websocket property to importMetaInjections with fallback logic (features.websocket ?? experimental.websocket); extends NitroImportMeta interface with optional _websocket?: boolean property.
Virtual feature-flags generation src/build/virtual/feature-flags.ts, src/runtime/virtual/feature-flags.ts	Removes hasWebSocket constant generation and export from both build-time and runtime feature-flags modules.
Build dev tooling src/build/vite/dev.ts	Inlines WebSocket feature check; replaces hasWebSocket variable with direct evaluation of nitro.options.features.websocket ?? nitro.options.experimental.websocket.
Runtime preset implementations src/presets/_nitro/runtime/nitro-dev.ts, src/presets/bun/runtime/bun.ts, src/presets/cloudflare/runtime/{cloudflare-durable,cloudflare-module,cloudflare-pages}.ts, src/presets/deno/runtime/{deno-deploy,deno-server}.ts, src/presets/node/runtime/{node-cluster,node-middleware,node-server}.ts, src/runtime/internal/vite/dev-entry.mjs	Replaces hasWebSocket imports and checks with import.meta._websocket for conditional WebSocket adapter initialization and upgrade handler registration across all preset runtimes.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~22 minutes

Possibly related PRs

• perf!: resolve virtual templates with single plugin #3819 — Directly refactors virtual feature-flags pipeline, including template changes and vfs handling related to feature-flag generation.
• refactor: env runners #3836 — Modifies WebSocket upgrade handling in src/build/vite/dev.ts with alternative worker/runner approach.
• feat: mock runtime virtual imports #3861 — Introduces and modifies virtual feature-flag exports and module IDs that interact with the hasWebSocket flag surface.

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/ws-shake

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