fix: joining paths from different layers with Ctrl+J fails

[Ayush2k02]

Summary

Screen.Recording.2025-12-27.at.6.41.56.AM.mov

Fixes #3519

This PR fixes the issue where joining paths from different layers with Ctrl+J fails because PointIds may change after merge_layers() runs due to ID collision resolution.

Details

When we try to join two points from different layers, we combine those layers into one. During this merge, the internal IDs of the points can change to avoid conflicts. The old code tried to connect the points immediately, but by then the IDs it was looking for didn't exist anymore. This fix works in three steps:

1. Save the locations first - Before merging the layers, remember where the two points are located on the canvas (their x,y coordinates)
2. Wait for the merge to finish - Let the layers merge completely. The merge happens in the background, so we schedule our next step to run after it's done
3. Find the points again and connect them - Once the merge is complete, look for points at the saved locations. These points might have new IDs now, but they're still in the same spot. Use these updated IDs to create the connecting line

[Keavon]

Hello and thanks for the PR. I need to mention that we do not accept PR descriptions written by AI because they increase the noise-to-signal ratio and usually serve to mislead with obscured inaccuracies. (The same applies to code, which must be written by you.)

[Ayush2k02]

Oh, hey , I had this extension turned on in my IDE https://whatthediff.ai/ , will be mindful to disable it when creating PRs in this repo :) . Also regarding using AI in code, I did use claude code for targeting the files and the fix but did review that intensively before publishing .

[Keavon]

Thanks for the insight into your process (we've been seeing more highly-elaborate-but-not-insightful PR descriptions like this and it's good to know some of the details about what kinds of AI tools are producing them). For code authorship, AI is acceptable for auto-completing lines you would already be typing, but we need contributions to always come from the original thought processes of its human authors who can answer to the reasoning behind each line of changes. Code can't be mysteriously changed without anyone aware of why the change was made. Thanks for working to follow our requirements to building an effective software project.