Remove file locking from gateway.log to enable concurrent read access

[Copilot]

The gateway.log file was using syscall.Flock with a shared lock, which could interfere with external processes attempting to read the log file. Additionally, buffered writes were not being flushed immediately, delaying log visibility.

Changes

• Removed file locking: Eliminated all syscall.Flock calls and the locked field from FileLogger
• Added immediate flushing: Call file.Sync() after each log write to ensure data is immediately visible
• Simplified Close(): Sync buffered data before closing, removed lock release logic
• Added integration test: Added TestBinaryInvocation_LogFileCreation to validate log file creation, permissions (0644), concurrent readability, startup message content, and immediate flushing behavior

Implementation

func (fl *FileLogger) Log(level LogLevel, category, format string, args ...interface{}) {
    // ... write log line ...
    
    // Flush immediately to ensure external processes can read
    if fl.logFile != nil {
        if err := fl.logFile.Sync(); err != nil {
            log.Printf("WARNING: Failed to sync log file: %v", err)
        }
    }
}

The file continues to use 0644 permissions, making it readable by all users without special access requirements.

Testing

• ✅ All unit tests pass (7/7 logger tests)
• ✅ All integration tests pass (17/17 tests including new log file test)
• ✅ New test validates log file creation, permissions, concurrent access, and immediate flushing
• ✅ Build and lint checks pass

Original prompt

Review how the gateway.log is opened so that it can be read by other processes.

• make sure the log is flushed to file often
• must not retain lock and not have special permissions
• must be readable by other users

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[pelikhan]

@copilot add test that do a run Md check creation of log file

[Copilot]

@copilot add test that do a run Md check creation of log file

Added TestBinaryInvocation_LogFileCreation that runs the binary and validates:

• Log file is created at specified --log-dir location
• File permissions are 0644 (readable by all)
• File is readable by other processes while gateway is running
• Content includes expected startup messages
• Immediate flushing works correctly

Test passes with all 17 integration tests ✓

Commit: 2e81caa