feat(db): rebuild Codex usage on upgrade and via maintenance action

Schema v16 wipes codex_session detail rows, _codex_session rollups and
Codex rollout cursors inside the migration savepoint (cursor deletion
uses pure shape matching so CODEX_HOME drift cannot orphan cursors);
the next session sync re-imports history from source JSONL under the
corrected importer. Fresh installs traverse the same branch as a no-op.

Add a manual "Rebuild Codex usage" maintenance action (single-flight,
hard-fail backup before reset, unconditional refresh notification even
when reimport is empty or fails after reset) with a destructive confirm
dialog, result toast and four-locale strings. Historical proxy-side
duplicate rows are intentionally left untouched; history whose source
JSONL was already deleted cannot be reconstructed.

src-tauri/src/commands/usage.rs

@@ -289,6 +289,35 @@ pub async fn sync_session_usage(
     .map_err(|error| AppError::Message(format!("会话用量同步任务失败: {error}")))
 }
 
+/// Codex reset 成功后，无论重导是否导入新行或返回错误，都必须通知前端刷新。
+/// 调用方应只在 reset 成功后调用，避免把未发生的数据变更误报为重建完成。
+fn finish_codex_rebuild(
+    result: Result<crate::services::session_usage::SessionSyncResult, AppError>,
+) -> Result<crate::services::session_usage::SessionSyncResult, AppError> {
+    crate::usage_events::notify_log_recorded();
+    result
+}
+
+/// 备份数据库后，仅重建 Codex session 用量。锁覆盖 backup → reset → import
+/// 整个序列，避免后台同步在清理和重导之间插入数据。
+#[tauri::command]
+pub async fn rebuild_codex_usage(
+    state: State<'_, AppState>,
+) -> Result<crate::services::session_usage::SessionSyncResult, AppError> {
+    let db = state.db.clone();
+    let _guard = crate::services::session_usage::session_sync_mutex()
+        .lock()
+        .await;
+    tauri::async_runtime::spawn_blocking(move || {
+        db.backup_database_file()?;
+        db.reset_codex_usage()?;
+        let result = crate::services::session_usage_codex::sync_codex_usage(&db);
+        finish_codex_rebuild(result)
+    })
+    .await
+    .map_err(|error| AppError::Message(format!("Codex 用量重建任务失败: {error}")))?
+}
+
 /// 获取数据来源分布
 #[tauri::command]
 pub fn get_usage_data_sources(
@@ -308,3 +337,33 @@ pub struct ModelPricingInfo {
     pub cache_read_cost_per_million: String,
     pub cache_creation_cost_per_million: String,
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn codex_rebuild_notifies_when_reimport_is_empty() {
+        crate::usage_events::take_test_notify_count();
+
+        let result = finish_codex_rebuild(Ok(
+            crate::services::session_usage::SessionSyncResult::default(),
+        ))
+        .expect("空重导应成功");
+
+        assert_eq!(result.imported, 0);
+        assert_eq!(crate::usage_events::take_test_notify_count(), 1);
+    }
+
+    #[test]
+    fn codex_rebuild_notifies_when_reimport_fails_after_reset() {
+        crate::usage_events::take_test_notify_count();
+
+        let result = finish_codex_rebuild(Err(AppError::Message(
+            "synthetic reimport failure".to_string(),
+        )));
+
+        assert!(result.is_err());
+        assert_eq!(crate::usage_events::take_test_notify_count(), 1);
+    }
+}