fix(client): propagate refreshed token save errors

[pragnyanramtha]

Summary

• move saveTokens(newTokens) outside the OAuth refresh failure catch
• preserve existing fallback-to-reauth behavior for refresh failures
• propagate post-refresh token persistence errors so rotated tokens are not silently lost

Fixes #2034.

Validation

• pnpm --dir packages/client exec vitest run test/client/auth.test.ts -t "propagates saveTokens errors"
• pnpm --dir packages/client exec vitest run test/client/auth.test.ts (168 passed)
• pnpm --filter @modelcontextprotocol/client typecheck
• pnpm --filter @modelcontextprotocol/client lint
• git diff --check

Note

The repo pre-push hook also ran full workspace checks, but the unrelated @modelcontextprotocol/test-helpers lint currently fails on vitest being imported from a package devDependency in existing test/helpers files. This PR only changes packages/client and the changeset.

[changeset-bot]

🦋 Changeset detected

Latest commit: 0eb334c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@modelcontextprotocol/client	Patch

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commit: 0eb334c