fix: resolve phantom subtask display on cancel during API retry (#4602)

[hannesrudolph]

Description

Fixes #4602

This PR resolves an issue where canceling a task during API retry would incorrectly display "Subtask Results" and create a checkpoint initialization loop, even though no subtask was actually created.

Changes Made

• Modified the clearTask handler in webviewMessageHandler.ts to check for the existence of a parentTask property instead of relying on stack size
• This ensures that only actual subtasks (tasks with a parent) trigger the finishSubTask() method
• Single tasks without parents now correctly use clearTask() instead

Testing

• All existing tests pass
• Added comprehensive test coverage in ClineProvider.spec.ts:
  • Test for single task without parent calling clearTask
  • Test for child task with parent calling finishSubTask
  • Test for handling when no current task exists
  • Test specifically validating the fix for issue Canceling API Retry Creates Phantom Subtask and Checkpoint Initialization Loop #4602
• Manual testing completed:
  • Started a task that triggers API retry
  • Canceled during the retry period
  • Verified no phantom "Subtask Results" appears
  • Verified no checkpoint initialization loop occurs

Verification of Acceptance Criteria

• When canceling during API retry, no "Subtask Results" display appears
• No checkpoint initialization loop is triggered
• The fix correctly distinguishes between actual subtasks and single tasks
• All tests pass and the implementation is properly tested

Checklist

• Code follows project style guidelines
• Self-review completed
• Comments added for complex logic
• Documentation updated (if needed)
• No breaking changes
• Tests added for the fix

Technical Details

The root cause was that the previous implementation checked provider.getClineStackSize() > 1 to determine if a task was a subtask. However, during API retry scenarios, the stack could have multiple entries even for a single task, leading to incorrect behavior.

The fix now properly checks for the existence of a parentTask property on the current task, which is the definitive way to determine if a task is actually a subtask.

---

Important

Fixes phantom subtask display issue by checking parentTask property in webviewMessageHandler.ts during task cancellation.

• Behavior:
  • Fixes issue Canceling API Retry Creates Phantom Subtask and Checkpoint Initialization Loop #4602 where canceling a task during API retry incorrectly displayed "Subtask Results" and caused a checkpoint loop.
  • clearTask in webviewMessageHandler.ts now checks for parentTask property instead of stack size to determine subtask status.
  • Only tasks with a parentTask trigger finishSubTask(); others use clearTask().
• Testing:
  • Added tests in ClineProvider.spec.ts for single tasks, child tasks, and no current task scenarios.
  • Test specifically validating the fix for issue Canceling API Retry Creates Phantom Subtask and Checkpoint Initialization Loop #4602 included.
  • Manual testing confirmed no phantom "Subtask Results" and no checkpoint loop on cancel during API retry.

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[Copilot]

Pull Request Overview

Fixes an issue where canceling during an API retry incorrectly treated single tasks as subtasks.

• Replace getClineStackSize() check with explicit parentTask existence in the clearTask handler
• Introduce a new clearTask() method on ClineProvider for non-subtask cancellations
• Add comprehensive tests for both subtask and single-task cancellation flows

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/core/webview/webviewMessageHandler.ts	Updated clearTask case to branch on currentTask.parentTask and call finishSubTask or clearTask
src/core/webview/ClineProvider.ts	Added clearTask() helper to remove the current task without subtask logic
src/core/webview/tests/ClineProvider.spec.ts	Added tests covering the new clearTask logic, including the fix for issue #4602

Comments suppressed due to low confidence (2)

src/core/webview/tests/ClineProvider.spec.ts:675

• This test does not mock or assert postStateToWebview; consider spying on provider.postStateToWebview to both avoid unintended side effects and verify that state is posted in this scenario.

			await messageHandler({ type: "clearTask" })

src/core/webview/webviewMessageHandler.ts:207

• The translation function t is used here but not imported in this module. Add the appropriate import (e.g. import { t } from 'i18n';) to prevent a runtime error.

				await provider.finishSubTask(t("common:tasks.canceled"))

[daniel-lxs]

LGMT