fix: properly serialize Error objects in debug logs

[craigvandotcom]

Problem

When errors occur during session execution (e.g., "Process exited unexpectedly"), the actual error details are lost in the logs:

[16:21:21.424] [remote]: launch error {}

The error object appears as {} because JSON.stringify() doesn't capture Error properties (message, stack, name) - they're not enumerable.

Solution

Added a serializeForLog() helper function that properly handles Error objects by explicitly extracting their non-enumerable properties.

Before

[16:21:21.424] [remote]: launch error {}

After

[16:21:21.424] [remote]: launch error {"name":"Error","message":"Connection refused","stack":"Error: Connection refused\n    at ..."}

Changes

• Added serializeForLog() helper function in src/ui/logger.ts
• Updated logToFile() to use the new helper
• Updated sendToRemoteServer() to use the same helper for consistency
• Added unit tests in src/ui/logger.test.ts

Testing

npx vitest run src/ui/logger.test.ts

All 7 tests pass:

• String passthrough
• Plain object serialization
• Error serialization with name, message, stack
• TypeError with correct name
• Additional enumerable properties on errors
• null/undefined handling
• number/boolean handling

Impact

This fix will help users and maintainers debug "Process exited unexpectedly" errors by capturing the actual error details in logs at ~/.happy/logs/.

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