Add tsgo as an opt-in fast type-checker

[kriszyp]

Summary

Companion to harper PR #1738. Wires up tsgo (TypeScript 7's native/Go-ported preview compiler) as a new opt-in npm run typecheck:fast script (plus a plain typecheck script for a stable baseline, per review) — invoked via npx, not a package.json dependency (see below).

Purpose

Benchmarked on this codebase (including the core/ submodule): tsgo --noEmit is ~7.2x faster than tsc --noEmit (3.17s → 0.44s). Usage is opt-in — the committed build script (still tsc, 5.x) is behaviorally untouched, though it shares this same tsconfig.json with the new script (harper-pro doesn't split build/check configs the way harper does).

Two tsconfig.json changes were needed, both verified byte-identical against tsc --noEmit before/after (isolated on one commit, config swapped in/out — 29/29 errors, no new/fixed errors either way):

• Removed "baseUrl": "." — TypeScript 7 hard-errors on it (TS5102, "Option baseUrl has been removed"). The existing "paths": {"@/*": ["./dist/*"]} is already relative and resolves identically without it; confirmed no bare imports anywhere in this repo (including the core/**/* included paths) rely on the baseUrl fallback.
• Pinned "strict": false" explicitly — this repo already had "noImplicitAny": false" as one strict sub-flag, but relied on tsc's implicit default (false) for the rest. TypeScript 7 flips that default to true; pinning it documents the status quo rather than changing behavior, and forward-guards a future compiler bump.

Not a devDependency (resolved review thread with @cb1kenobi): an earlier version of this PR added @typescript/native-preview as a plain devDependency. Chris correctly pointed out that made npm ci fetch this exact nightly tarball for every CI job (unit, integration, smoke, stress), not just the opt-in checker — if that specific tarball is ever pruned from the registry, all of those jobs would fail, not just typecheck:fast. optionalDependencies doesn't fix this either: both harper and harper-pro are genuinely public npm packages (verified against the registry — no private field), so that would install-attempt this dev-only tool for every real end-user's npm install. Chris's suggested fix — invoke it on demand via npx -y -p @typescript/native-preview@<pinned-version> tsgo ... instead of adding it as a dependency at all — confines a pruned-tarball failure to typecheck:fast alone, matching its actually-opt-in nature. Trade-off: no package-lock.json integrity-hash pinning for this tool (the version is still pinned in the npx invocation itself, just not hash-verified against a lockfile entry).

Where to focus review attention

• The baseUrl removal touches the tsconfig that also drives the real build — verified inert (see above), but flagging since it's shared config, not an isolated checker-only file.
• Same 4 known tsgo findings as harper (this repo's core/ is the same submodule code) plus one more: replication/subscriptionManager.ts hits the same manageThreads.js dynamic-export resolution gap. None introduced by this PR; the manageThreads ones are already fixed as a side effect of harper chore: Sync Core #562's CJS→ESM conversion once that lands.

Generated by Claude (Opus 4.8).

[socket-security]

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👍 No dependency changes detected in pull request

[claude]

Reviewed; no blockers found.

[gemini-code-assist]

Code Review

This pull request introduces the @typescript/native-preview package and adds a fast type-checking script (typecheck:fast) using tsgo. It also updates tsconfig.json by explicitly disabling strict mode and removing the deprecated baseUrl option. The feedback suggests adding a standard typecheck script using tsc to serve as a stable baseline for comparison.