| @modelcontextprotocol/client | patch |
|---|---|
| @modelcontextprotocol/server | patch |
instanceof on the SDK error classes (ProtocolError and its typed subclasses, SdkError/SdkHttpError, OAuthError, and the client's SseError, UnauthorizedError, and OAuth-client-flow error family — OAuthClientFlowError and its subclasses) now works across separately bundled copies of the SDK. The classes match by a stable brand (via Symbol.hasInstance and a registry symbol) instead of prototype identity, so a process that uses both @modelcontextprotocol/client and @modelcontextprotocol/server - a gateway, host, or in-process test - can check errors constructed by either package against the class re-exported by the other. Ordinary prototype-based instanceof is preserved as a fallback; user-defined subclasses keep plain prototype semantics. Notes: cross-bundle matching requires both copies to be at or after this release; brands assert identity, not field shape, across versions - keep reading fields defensively. As a side effect, a foreign-bundle SdkError used as an abort reason is now rethrown as-is instead of being wrapped as a RequestTimeout. Branded hierarchies additionally expose an explicit static guard, X.isInstance(value), that reads the same brand and narrows in TypeScript — an alternative for codebases that prefer predicate-style checks over instanceof. Also: UnauthorizedError now sets error.name to 'UnauthorizedError' (previously 'Error'), and per-package conformance tests enforce that every exported error class participates in branding. Version-negotiation probing now recognizes UnauthorizedError (previously a dead name-string check) and propagates it unchanged, so connect() on an auth-gated server rejects with the original UnauthorizedError (previously wrapped as the cause of an SdkError(EraNegotiationFailed)) — run finishAuth() and reconnect, and the retry probes with the token.