feat(client): add runtime isError guards to all public ...Error unions

[cesarenaldi]

Summary

• Adds a makeErrorGuard(...classes) helper in errors.ts that takes concrete error constructors and returns { isError(error: unknown): error is Union } via instanceof checks — the union type is inferred from the constructor tuple
• Adds a same-named export const FooError = makeErrorGuard(...) alongside every export type FooError union across 27 source files (all action files, abis.ts, types.ts, workflow.ts)
• Re-exports ./actions from the root index.ts so guards are accessible from @polymarket/client without a sub-path import
• Adds errors.test.ts with 3 tests covering positive hits, non-SDK rejection, and type-narrowing

Consumer ergonomics

try {
  await client.listMarkets();
} catch (error) {
  if (ListMarketsError.isError(error)) {
    switch (error.name) {
      case 'RateLimitError':
        // retry...
        break;
      case 'RequestRejectedError':
        // handle 4xx...
        break;
    }
  }
}

Both the existing import type { ListMarketsError } (union type) and the new import { ListMarketsError } (guard object) are exported under the same name, using TypeScript's separate type/value namespaces — no breaking change.

Design notes

• Guard uses instanceof, not error.name string matching, so subclasses are handled correctly
• For alias unions (PrepareMarketOrderPostingError = PrepareMarketOrderError), the const is a direct reference to the parent guard — no duplication
• For composed unions in gasless.ts where the inner type is module-private (ExecuteGaslessError), the classes are flattened at the call site
• WaitForTransactionError in types.ts imports classes directly from ./errors to avoid a circular value dependency through ./actions

Test plan

• pnpm lint — clean
• pnpm typecheck — clean
• pnpm vitest run --project client packages/client/src/errors.test.ts — 3/3 pass

🤖 Generated with Claude Code

---

Note

Low Risk
Low risk: changes are additive (new makeErrorGuard helper and exported guard values) and don’t alter request/transaction behavior, but they do expand the public API surface via additional exports.

Overview
Adds a generic makeErrorGuard(...classes) helper and, alongside each existing ...Error type union, exports a same-named const with an isError(error) runtime type guard inferred from the provided error constructors.

Updates decorators to re-export these error guards/unions per action group, adjusts root exports (including AuthenticateWithError/CompleteWithError) so consumers can import guards from the package entrypoint, and adds a small vitest suite validating guard behavior and TypeScript narrowing.

^{Reviewed by Cursor Bugbot for commit 6af2b1f. Bugbot is set up for automated code reviews on this repo. Configure here.}