Fix JSON log attribute consistency and double encoding

- Change tenant_name to tenant in AccessLogEntry for consistency
- Improve JSONLogWriter to detect and pass through Rails JSON logs directly
- Prevent double JSON encoding of application logs
- Maintain consistency across navigator access logs and Rails app logs

The JSONLogWriter now checks if incoming logs are already JSON formatted
with @timestamp and severity fields (indicating Rails JSON output) and
passes them through directly instead of wrapping them again.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: rubys

cmd/navigator/main.go

@@ -400,6 +400,7 @@ type LogEntry struct {
 }
 
 // JSONLogWriter writes structured JSON log entries
+// It can pass through JSON from the application or wrap plain text in JSON
 type JSONLogWriter struct {
 	source string
 	stream string
@@ -414,6 +415,24 @@ func (w *JSONLogWriter) Write(p []byte) (n int, err error) {
 		if len(line) == 0 {
 			continue
 		}
+
+		// Check if the line is already valid JSON from the Rails app
+		// Rails JSON logs should have @timestamp, severity, message, source, tenant fields
+		var existingEntry map[string]interface{}
+		if err := json.Unmarshal(line, &existingEntry); err == nil {
+			// It's valid JSON - check if it looks like our Rails JSON format
+			if _, hasTimestamp := existingEntry["@timestamp"]; hasTimestamp {
+				if _, hasSeverity := existingEntry["severity"]; hasSeverity {
+					// This looks like Rails JSON output - pass it through directly
+					// Just ensure it has proper newline
+					w.output.Write(line)
+					w.output.Write([]byte("\n"))
+					continue
+				}
+			}
+		}
+
+		// Not JSON or not Rails JSON format - wrap it in our JSON structure
 		entry := LogEntry{
 			Timestamp: time.Now().Format(time.RFC3339),
 			Source:    w.source,
@@ -503,7 +522,7 @@ type AccessLogEntry struct {
 	Referer         string `json:"referer"`
 	UserAgent       string `json:"user_agent"`
 	FlyRequestID    string `json:"fly_request_id"`
-	TenantName      string `json:"tenant_name,omitempty"`
+	Tenant          string `json:"tenant,omitempty"`
 }
 
 // logTenantRequest logs a tenant request in JSON format matching nginx log format
@@ -551,7 +570,7 @@ func logTenantRequest(r *http.Request, recorder *responseRecorder, tenantName st
 		Referer:       referer,
 		UserAgent:     userAgent,
 		FlyRequestID:  r.Header.Get("Fly-Request-Id"),
-		TenantName:    tenantName,
+		Tenant:        tenantName,
 	}
 
 	data, _ := json.Marshal(entry)