Express app.listen's callback accepts an optional error argument, which needs checking to avoid surprising behaviour.

(note: README.md already shows an example of such error handling)

Motivation and Context

When one of the ports used by the examples is already in use, users will unknowingly hit the previously running server instead of being notified of an error.

How Has This Been Tested?

Concurrent runs of npx -y tsx src/examples/server/simpleStreamableHttp.ts and its sibling examples.

Breaking Changes

None

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed