fix: show notification when corrupt task fails to load

- Added error handling in showTaskWithId to catch when getTaskWithId fails
- Added new i18n error message "task_corrupt_deleted" to explain the issue
- Added comprehensive unit tests for the showTaskWithId method
- Refreshes webview state after showing the error notification

Fixes #6592

Author: roomote

src/core/webview/ClineProvider.ts

@@ -1343,8 +1343,16 @@ export class ClineProvider
 	async showTaskWithId(id: string) {
 		if (id !== this.getCurrentCline()?.taskId) {
 			// Non-current task.
-			const { historyItem } = await this.getTaskWithId(id)
-			await this.initClineWithHistoryItem(historyItem) // Clears existing task.
+			try {
+				const { historyItem } = await this.getTaskWithId(id)
+				await this.initClineWithHistoryItem(historyItem) // Clears existing task.
+			} catch (error) {
+				// Task not found or corrupt - it has already been deleted from state by getTaskWithId
+				vscode.window.showErrorMessage(t("common:errors.task_corrupt_deleted"))
+				// Refresh the webview to update the task list
+				await this.postStateToWebview()
+				return
+			}
 		}
 
 		await this.postMessageToWebview({ type: "action", action: "chatButtonClicked" })