perf(usage): coalesce session-sync notifications and serialize sync execution

Replace per-insert usage notifications with a single notification per
sync pass, guard all sync entry points (startup backfill, 60s loop,
manual sync) behind a process-wide single-flight tokio mutex, and move
blocking file/DB work onto spawn_blocking with MissedTickBehavior::Skip.

Extend SessionSyncResult with deferredFiles/suspectedDuplicates
observability fields (saturating aggregation) and add a test seam that
counts notifications even without an injected AppHandle.

src-tauri/src/commands/usage.rs

@@ -275,52 +275,18 @@ pub fn delete_model_pricing(state: State<'_, AppState>, model_id: String) -> Res
 
 /// 手动触发会话日志同步
 #[tauri::command]
-pub fn sync_session_usage(
+pub async fn sync_session_usage(
     state: State<'_, AppState>,
 ) -> Result<crate::services::session_usage::SessionSyncResult, AppError> {
-    // 同步 Claude 会话日志
-    let mut result = crate::services::session_usage::sync_claude_session_logs(&state.db)?;
-
-    // 同步 Codex 使用数据
-    match crate::services::session_usage_codex::sync_codex_usage(&state.db) {
-        Ok(codex_result) => {
-            result.imported += codex_result.imported;
-            result.skipped += codex_result.skipped;
-            result.files_scanned += codex_result.files_scanned;
-            result.errors.extend(codex_result.errors);
-        }
-        Err(e) => {
-            result.errors.push(format!("Codex 同步失败: {e}"));
-        }
-    }
-
-    // 同步 Gemini 使用数据
-    match crate::services::session_usage_gemini::sync_gemini_usage(&state.db) {
-        Ok(gemini_result) => {
-            result.imported += gemini_result.imported;
-            result.skipped += gemini_result.skipped;
-            result.files_scanned += gemini_result.files_scanned;
-            result.errors.extend(gemini_result.errors);
-        }
-        Err(e) => {
-            result.errors.push(format!("Gemini 同步失败: {e}"));
-        }
-    }
-
-    // 同步 OpenCode 使用数据
-    match crate::services::session_usage_opencode::sync_opencode_usage(&state.db) {
-        Ok(opencode_result) => {
-            result.imported += opencode_result.imported;
-            result.skipped += opencode_result.skipped;
-            result.files_scanned += opencode_result.files_scanned;
-            result.errors.extend(opencode_result.errors);
-        }
-        Err(e) => {
-            result.errors.push(format!("OpenCode 同步失败: {e}"));
-        }
-    }
-
-    Ok(result)
+    let db = state.db.clone();
+    let _guard = crate::services::session_usage::session_sync_mutex()
+        .lock()
+        .await;
+    tauri::async_runtime::spawn_blocking(move || {
+        crate::services::session_usage::sync_all_unlocked(&db)
+    })
+    .await
+    .map_err(|error| AppError::Message(format!("会话用量同步任务失败: {error}")))
 }
 
 /// 获取数据来源分布