🧹 [Code Health] Use structured logger in Relay Server

[anusornc]

🎯 What: The code health issue addressed was using console.log and console.error directly inside src/relay/server.ts. These were replaced with the centralized relayLogger defined in src/utils/logger.ts. Error logging correctly wraps exception objects inside the structured logging metadata payload.

💡 Why: This improves maintainability and readability by keeping structured logs uniform across the protocol, making logs easier to parse in monitoring tools (like Prometheus or external observability stacks). It removes hardcoded [Relay] string prefixes that exist elsewhere, delegating formatting logic entirely to the logger itself.

✅ Verification: Verified that npx vitest run and npm run build continue to succeed with no regressions, and that relayLogger is correctly integrated. The code review confirmed all changes were applied safely.

✨ Result: Improved maintainability, consistency, and better observability of the RelayServer code.

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PR created automatically by Jules for task 16151916548099373614 started by @anusornc

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[gemini-code-assist]

Code Review

This pull request replaces standard console logging with structured logging using relayLogger in src/relay/server.ts. The feedback highlights that passing raw Error objects directly to the structured logger will cause them to serialize as empty objects, losing critical error details and stack traces. Additionally, logging a multi-line ASCII art banner using a structured logger will result in escaped newline characters, making it hard to read in log aggregators; this should be replaced with a clean, single-line message with structured metadata.

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[gemini-code-assist]

In JavaScript/TypeScript, Error objects do not have enumerable properties (like message and stack). When passed directly to JSON.stringify (which relayLogger uses under the hood), they serialize to an empty object {}. This means the actual error details and stack trace will be completely lost in your structured logs.

To preserve this critical diagnostic information, extract the error's message and stack trace explicitly.

Suggested change

	relayLogger.error('Invalid message format', { error: err });
	relayLogger.error('Invalid message format', {
	error: err instanceof Error ? err.message : String(err),
	stack: err instanceof Error ? err.stack : undefined,
	});

[gemini-code-assist]

In JavaScript/TypeScript, Error objects do not have enumerable properties (like message and stack). When passed directly to JSON.stringify (which relayLogger uses under the hood), they serialize to an empty object {}. This means the actual error details and stack trace will be completely lost in your structured logs.

To preserve this critical diagnostic information, extract the error's message and stack trace explicitly.

        relayLogger.error('Socket error', {
          error: err instanceof Error ? err.message : String(err),
          stack: err instanceof Error ? err.stack : undefined,
        });

[gemini-code-assist]

In JavaScript/TypeScript, Error objects do not have enumerable properties (like message and stack). When passed directly to JSON.stringify (which relayLogger uses under the hood), they serialize to an empty object {}. This means the actual error details and stack trace will be completely lost in your structured logs.

To preserve this critical diagnostic information, extract the error's message and stack trace explicitly.

  relay.start().catch((err: any) =>
    relayLogger.error('Failed to start server', {
      error: err instanceof Error ? err.message : String(err),
      stack: err instanceof Error ? err.stack : undefined,
    })
  );

[gemini-code-assist]

Logging a multi-line ASCII art banner using a structured JSON logger (relayLogger.info) will result in a single log entry with escaped newline characters (\n), making it extremely difficult to read in log aggregation tools (e.g., Kibana, Datadog, or CloudWatch).

Since relayLogger is a structured logger, it is highly recommended to log a clean, single-line message and pass the server configuration details as structured metadata instead. For example:

relayLogger.info('DAP Relay Server started successfully', {
  version: '1.0.0',
  host: this.config.host,
  port: this._boundPort,
  wsUrl: `ws://${this.config.host}:${this._boundPort}/ws`,
  apiKeys: this.config.apiKeys.length > 0 ? this.config.apiKeys : 'open',
  heartbeatIntervalMs: this.config.heartbeatIntervalMs,
  tls: this.config.enableTls ? 'enabled' : 'disabled'
});