Fix pen tool preview line disappearing during undo

[Ankitt-02]

Summary

Fixes an issue where the Pen tool preview line could disappear after repeatedly undoing while drawing a path.

The undo flow restored anchor history state but did not fully restore the temporary preview/handle continuation state used by the active Pen tool session. This caused the preview segment from the last anchor point to the cursor to stop rendering consistently after multiple undo operations.

Changes

Updated the Pen tool undo handling to restore transient preview-related state during undo operations by refreshing:

• next_point
• next_handle_start
• handle_end

This keeps the preview segment active and consistent while continuing to draw after repeated undo actions.

Testing

Tested by:

• creating polyline paths
• repeatedly undoing points
• continuing path drawing after undo
• verifying the preview line remains visible and interactive

Closes #3790

[cubic-dev-ai]

No issues found across 1 file

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Re-trigger cubic}

[gemini-code-assist]

Code Review

This pull request updates the pen tool's undo logic to reset point data when stepping back. The reviewer identified that the assignments to next_point and next_handle_start are redundant because they are immediately overwritten in the subsequent place_anchor call, and suggested only keeping the update to handle_end.