fix(client): surface OAuth token persistence failures

[he-yufeng]

Summary

Fixes #2034.

When OAuth refresh succeeds but provider.saveTokens() fails, auth() should surface that persistence failure. The authorization server may already have rotated the refresh token, so silently falling through to a new authorization flow can hide the only useful error and leave the client with stale credentials.

This keeps the existing fallback behavior for refresh request failures, but moves saveTokens() out of that catch block so store/I/O failures propagate normally.

To verify

• pnpm --filter @modelcontextprotocol/client exec vitest run test/client/auth.test.ts -t "does not hide token persistence failures"
• pnpm --filter @modelcontextprotocol/client exec vitest run test/client/auth.test.ts
• pnpm --filter @modelcontextprotocol/client typecheck
• pnpm --filter @modelcontextprotocol/client lint
• git diff --check

The repository pre-push hook also ran workspace typecheck, build, and lint successfully.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 34c5df5

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[pkg-pr-new]

Open in StackBlitz

@modelcontextprotocol/client

npm i https://pkg.pr.new/@modelcontextprotocol/client@2121

@modelcontextprotocol/server

npm i https://pkg.pr.new/@modelcontextprotocol/server@2121

@modelcontextprotocol/express

npm i https://pkg.pr.new/@modelcontextprotocol/express@2121

@modelcontextprotocol/fastify

npm i https://pkg.pr.new/@modelcontextprotocol/fastify@2121

@modelcontextprotocol/hono

npm i https://pkg.pr.new/@modelcontextprotocol/hono@2121

@modelcontextprotocol/node

npm i https://pkg.pr.new/@modelcontextprotocol/node@2121

commit: 34c5df5

[he-yufeng]

The red CI job is the existing Cloudflare Workers/Miniflare flaky path ( est/server/cloudflareWorkers.test.ts: Network connection lost). The OAuth test, full client auth test file, typecheck, lint, and pre-push workspace checks pass locally. I don't have repository admin rights to rerun the failed job.