Investigate platform-bun routing and cross-platform HTTP performance

[ayden94]

Summary

Follow-up from the Fastify native performance work: verify whether the shared dispatcher optimization benefits other platform-* adapters, and fix the local platform-bun benchmark route mismatch that currently blocks measurement.

Observed

• platform-fastify has a confirmed benchmark improvement from the dedicated adapter optimization plus shared dispatcher change.
• Local fluo+Bun HTTP comparison returned 404 No handler registered for GET /tenants/t-001/users, so Bun could not be included in the final benchmark gate.
• platform-bun and platform-cloudflare-workers use the runtime/web request factory, so the shared dispatcher change may help, but this is not yet measured.
• Other Node-style platforms may have smaller or no impact depending on whether headers are already eagerly snapshotted.

Scope

• Reproduce and fix the platform-bun benchmark route registration/matching issue.
• Add focused regression coverage for the route behavior.
• Run short targeted benchmark checks for available platform-* adapters after Bun is measurable.
• Keep changes in a dedicated .worktrees/ branch.

Out of scope

• Publishing packages locally.
• Merging PRs.
• Broad benchmark harness rewrites unless required for a reliable targeted measurement.