feat(eslint-plugin-runner): new package for ESLint plugin compatibility runtime

[fansenze]

Summary

Adds @rslint/eslint-plugin-runner as a new self-contained npm package.

The runner executes unmodified ESLint v10 plugin rules inside Node worker_threads. It exposes:

• WorkerPool — queued task model with per-task SharedArrayBuffer cancel flag, per-task timeout, worker lifecycle (spawn / respawn-on-crash / shutdown drain), and a postMessage failure path that distinguishes unserializable-payload errors from a dead worker.
• LintWorker entry — imports user rslint configs directly, extracts live plugin instances keyed by configDirectory, and dispatches lint tasks per configKey.
• ESLint v10 surface fills used by ported plugin rules — Rule.Context, SourceCode (lazy tokens + getDisableDirectives), and scope analysis (eslint-scope for JS/JSX, @typescript-eslint/scope-manager for TS).
• A self-contained tokenizer — oxc-parser emits no token list, so the package rebuilds an espree-compatible token stream for JS/TS/JSX/TSX (incl. JSX character-reference decoding and regex/division disambiguation).
• AST layer — oxc-parser (ESTree mode, preserveParens: false) normalized to the shape ESLint v10 / @typescript-eslint/parser declare (range/loc, parent links, traversal driven by oxc-parser's own visitorKeys).
• IPC client — framed protocol scaffold for the future host's reverse-RPC.

Self-contained: no upstream caller in this PR. Build and tests run without any other workspace package.

pnpm --filter @rslint/eslint-plugin-runner build
pnpm --filter @rslint/eslint-plugin-runner test

554 tests across 28 files, all pass standalone. ESLint-API / token / AST / scope behaviors are pinned against espree@11.2.0 + eslint@10.4.0 differential oracles. The worker-pool-e2e suite (driven by a local fixture plugin) covers the queue model, cancellation, per-task timeout + respawn, shutdown drain, and postMessage failure modes; remaining suites exercise the tokenizer, AST normalization, SourceCode / Rule.Context, scope factory, listener merge, diagnostic builder, plugin loader, cancel flag, and the IPC client.

Runtime deps: @typescript-eslint/scope-manager, eslint-scope, esquery, globals, oxc-parser. Peer dep: jiti (optional). ESM-only ("type": "module").

Related Links

N/A

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

[gemini-code-assist]

Code Review

This pull request introduces the @rslint/eslint-plugin-runner package, which provides an internal ESLint-plugin compatibility runtime for rslint, supporting ESLint v10 APIs and executing rules on a Node worker_threads pool. The implementation covers the full linting pipeline, including AST normalization, scope analysis, and a custom tokenizer, alongside a bidirectional IPC client for communication with the Go binary. Review feedback focuses on performance and safety improvements, specifically recommending caching for merged token streams, adopting visitorKeys for more efficient AST traversal in getNodeByRangeIndex, and using binary search to optimize token lookups in isSpaceBetween. A safety concern regarding potential out-of-bounds array access during character offset conversion was also raised.