[codex] adopt Effect for transform executor cleanup

[ScriptedAlchemy]

Summary

• documents the incremental Effect adoption design and implementation plan
• adds effect as an internal runtime dependency
• introduces a small Effect boundary helper for plugin internals
• migrates route transform executor close cleanup to an Effect-backed program while preserving the existing Promise API
• adds lifecycle coverage for in-flight close rejection, idempotent close, run-after-close inline fallback, and source-cache recovery after postMessage failure

Notes

This PR is stacked on codex/parallel-dev-compilers. Effect is kept out of generated React Router framework code and out of public plugin APIs.

Verification

• corepack pnpm exec rstest run -c ./rstest.config.ts tests/parallel-route-transforms.test.ts
• corepack pnpm run test:core
• corepack pnpm exec tsc --noEmit
• corepack pnpm run format:check
• corepack pnpm run build
• corepack pnpm run test:package-interop
• git diff --check

[pkg-pr-new]

Open in StackBlitz

pnpm add https://pkg.pr.new/rsbuild-plugin-react-router@01df6b5

commit: 01df6b5

[github-actions]

Benchmark Results

Compared PR head 928b383 against base 2d960ac.

Total median wall time: 11.08s -> 10.03s (-9.5%, 1.11x speedup)
Compiler ready median: 9.20s -> 8.04s (-12.6%)
Route load median: 1.83s -> 1.85s (+1.2%)

Benchmark	Base total	Head total	Delta	Head ready	Head routes	Speedup	Head RSS p95
large-355-ssr-esm	11.08s	10.03s	-9.5%	8.04s	1.85s	1.11x	-

Profile: large; mode: dev; iterations: 10; warmup: 0.
Workflow run