fix(obs): harden cleaner file matching (#4486)

Co-authored-by: heihutu <heihutu@gmail.com>

crates/obs/src/telemetry/local.rs

@@ -315,7 +315,8 @@ fn init_file_logging_internal(
     is_production: bool,
 ) -> Result<OtelGuard, TelemetryError> {
     let service_name = config.service_name.as_deref().unwrap_or(APP_NAME);
-    let log_filename = config.log_filename.as_deref().unwrap_or(service_name);
+    let resolved_log_filename = resolve_log_cleanup_file_pattern(config, service_name);
+    let log_filename = resolved_log_filename.as_str();
     let keep_files = config.log_keep_files.unwrap_or(DEFAULT_LOG_KEEP_FILES);
 
     // ── 1. Ensure the log directory exists ───────────────────────────────────
@@ -523,7 +524,7 @@ pub fn spawn_cleanup_task(
     let log_dir = std::path::PathBuf::from(log_directory);
     // Use suffix matching for log files like `2026-03-01-06-21.rustfs.log`
     // where `rustfs.log` is the stable suffix generated by the rolling appender.
-    let file_pattern = config.log_filename.as_deref().unwrap_or(log_filename).to_string();
+    let file_pattern = resolve_log_cleanup_file_pattern(config, log_filename);
     let active_filename = file_pattern.clone();
 
     // Determine match mode from config, defaulting to the repository-wide
@@ -648,6 +649,13 @@ pub fn spawn_cleanup_task(
     })
 }
 
+fn resolve_log_cleanup_file_pattern(config: &OtelConfig, fallback_log_filename: &str) -> String {
+    match config.log_filename.as_deref() {
+        Some(candidate) if !candidate.trim().is_empty() => candidate.to_string(),
+        _ => fallback_log_filename.to_string(),
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -900,4 +908,14 @@ mod tests {
 
         assert_eq!(resolve_log_cleanup_interval_seconds(&config), DEFAULT_OBS_LOG_CLEANUP_INTERVAL_SECONDS);
     }
+
+    #[test]
+    fn empty_cleanup_pattern_falls_back_to_runtime_log_filename() {
+        let config = OtelConfig {
+            log_filename: Some("   ".to_string()),
+            ..OtelConfig::default()
+        };
+
+        assert_eq!(resolve_log_cleanup_file_pattern(&config, "rustfs.log"), "rustfs.log");
+    }
 }