[SawyerHood]

Human comments

What was wrong

Typechecking ran on TypeScript 7.0.2 (typescript-7 → npm:typescript@^7.0.2). tsrs, the Rust port of the TypeScript 7 compiler, is roughly twice as fast and uses half the memory on bb (numbers below). This PR moves bb's typechecking to it.

tsrs 0.18.0 is a faithful port of TypeScript 7.1.0-dev.20260930.4 and prints the same diagnostics. Moving to it therefore also moves bb onto a 7.1 nightly, which brings two upstream regressions. tsrs also has no Windows binary yet:

1. TS5115 on zod's z.json() ("Instantiations of the following types appear infinitely circular: 'IsOptionalIn', '$ZodTypeInternals', '$InferZodRecordInput'"). Reported as TS5115 in published Zod 4.5–4.6 types after #64372 microsoft/TypeScript#64605. The first nightly that fails is 7.1.0-dev.20260929.1, after Restore idempotency to resolveObjectTypeMembers microsoft/TypeScript#64372.
2. TS7031 on a contextually typed destructured parameter with = {}. Reported as TS7031 false positive for nested object binding pattern with = {} default in an annotated parameter (regression from #64043) microsoft/TypeScript#64431, with fixes proposed in Fix false implicit-any errors in annotated nested bindings microsoft/TypeScript#64440 and Do not pad binding elements that the parameter's type already types microsoft/TypeScript#64671. The first nightly that fails is 7.1.0-dev.20260923.1.
3. No win32-x64 package through 0.18.0. tsrs's npm/README.md says its release workflow now builds one. Intel Macs remain unsupported.

What changed

• tsrs replaces TypeScript 7 for typechecking. Every package.json that listed typescript-7 now lists tsrs pinned to 0.18.0-ts7.1.0-dev.20260929 (exact pin because the releases are experimental), and every typecheck script runs tsrs --noEmit. typescript (the @typescript/typescript6 JS API) stays for tooling that imports it.
• Workaround for regression 1. Core code uses jsonValueSchema/jsonObjectSchema from @bb/domain instead of z.json(): apps/desktop (CDP + capture, plus two tests) and packages/desktop-contract. Forkable plugins can't import @bb/domain, so account-pool, bb-account, connect, mcp and workflows each define the same z.lazy schema, typed with the SDK's JsonValue. That schema has the same structure as zod's z.json(), so runtime validation is unchanged. The only remaining z.json() calls are in two tests that don't trigger the error.
• Workaround for regression 2. The abort-signal mock in system-config-atoms.local-access.test.ts annotates its parameter.
• Windows. The windows-foundation job now runs lint test without typecheck. The Windows typecheck steps in build-desktop.yml and the nightly-desktop-windows job are removed. plugin-authoring-doc-examples.test.ts now launches tsrs and skips on win32. Types don't depend on the OS, and the Linux static-checks job still typechecks every package. These can come back once tsrs publishes win32-x64.
• Left alone: the plugin scaffold's typescript dependency for user plugins, and the bb-app tarball smoke test's npx typescript consumer check. Both stand in for what plugin authors and SDK users run.

How you verified

• pnpm exec turbo run typecheck --force --continue on tsrs: 105/105 pass. Before the workarounds, 7 failed, with 16 TS5115 errors and 1 TS7031.

• Every changed package also passes tsc --noEmit on TypeScript 7.0.2.

• Both regressions reproduce on tsc 7.1.0-dev.20260930.4 and today's 7.1.0-dev.20261020.3, and pass on 7.0.2. I found the first failing nightly for each by trying successive builds.

• turbo run lint test for @bb/desktop, @bb/desktop-contract, account-pool, bb-account, connect, bb--mcp and workflows: 16/16 pass. The doc-examples test passes with tsrs, and the system-config atoms test passes (12/12).

• Speed, same machine, warm, --noEmit, best of two runs:

  package	tsc (TS 7.0.2)	tsrs
  apps/server	11.3s, 3.3 GB	5.5s, 1.6 GB
  apps/app	11.4s, 3.4 GB	6.4s, 1.7 GB

• pnpm install --frozen-lockfile is clean, and oxfmt --check passes.

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