Documentation Lambda handler resolution fallback mechanism for Node.js runtime

[ibaraki-douji]

The current documentation doesn't fully explain how Lambda resolves handler paths when they don't exactly match the file structure.

Missing Documentation: Lambda appears to have fallback logic in handler resolution that isn't documented. When a handler is configured as lib/handler.run but the file exists at /var/task/handler.js, Lambda successfully finds and executes the handler despite the path mismatch.

Evidence:

• Handler config: lib/handler.run
• File location: /var/task/handler.js
• Result: Function works
• Node.js test: require.resolve("lib/handler") fails

Request: Please add documentation explaining:

1. Lambda's complete handler resolution algorithm
2. Any fallback mechanisms used when exact paths aren't found
3. Whether this behavior is guaranteed across runtime versions

Suggested Location: This information would fit well in the "Define Lambda function handler in Node.js" documentation section.