Add Alt+Drag layer duplication to Layers Panel

[afrdbaig7]

Implements Alt+Drag duplication in Layers.svelte and exposes a WASM API for duplicating the current layer selection. Behavior matches the Select Tool, including modifier changes during drag and focus loss handling.

Fixes #2824

[timon-schelling]

This contains commits from other PRs. Please only include the relevant commit.

[afrdbaig7]

sorry about that i will fix it now

[Keavon]

Please give this a try, it seems to be catastrophically broken (maybe something changed with the surrounding code as a result of the rebase?).

[Keavon]

Hi, do you have any updates on this? Could you please resolve the merge conflict, confirm it works in the latest, and mark it as ready for review (and reply so I get an email about it)? I really do look forward to merging this feature, thank you!

[afrdbaig7]

Hi, do you have any updates on this? Could you please resolve the merge conflict, confirm it works in the latest, and mark it as ready for review (and reply so I get an email about it)? I really do look forward to merging this feature, thank you!

ok keavon i will resolve the merge conflicts and will test against the latest changes and will push an update shortly

[cubic-dev-ai]

2 issues found across 2 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="frontend/src/components/panels/Layers.svelte">

<violation number="1" location="frontend/src/components/panels/Layers.svelte:109">
P2: The blur event listener uses an anonymous function and is never removed in `onDestroy`, causing a listener leak on each HMR cycle. Extract the callback into a named function (like the other handlers) and add the corresponding `removeEventListener` in `onDestroy`.</violation>

<violation number="2" location="frontend/src/components/panels/Layers.svelte:472">
P1: Race condition: `startDuplicates()` is async but not awaited. If Alt is released (or the drag is aborted) before `await tick()` resolves, `duplicatedLayerIds` is still `undefined`, so `stopDuplicates()` silently bails out — leaving orphaned duplicate layers in the document. Consider making the duplication fully synchronous, or guarding against this by tracking/awaiting the pending promise.</violation>
</file>

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[cubic-dev-ai]

P1: Race condition: startDuplicates() is async but not awaited. If Alt is released (or the drag is aborted) before await tick() resolves, duplicatedLayerIds is still undefined, so stopDuplicates() silently bails out — leaving orphaned duplicate layers in the document. Consider making the duplication fully synchronous, or guarding against this by tracking/awaiting the pending promise.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At frontend/src/components/panels/Layers.svelte, line 472:

<comment>Race condition: `startDuplicates()` is async but not awaited. If Alt is released (or the drag is aborted) before `await tick()` resolves, `duplicatedLayerIds` is still `undefined`, so `stopDuplicates()` silently bails out — leaving orphaned duplicate layers in the document. Consider making the duplication fully synchronous, or guarding against this by tracking/awaiting the pending promise.</comment>

<file context>
@@ -424,6 +466,18 @@
+
+		if (e.key === "Alt" && internalDragState?.active && !altKeyPressedDuringDrag) {
+			altKeyPressedDuringDrag = true;
+			startDuplicates();
+		}
+	}
</file context>

[cubic-dev-ai]

P2: The blur event listener uses an anonymous function and is never removed in onDestroy, causing a listener leak on each HMR cycle. Extract the callback into a named function (like the other handlers) and add the corresponding removeEventListener in onDestroy.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At frontend/src/components/panels/Layers.svelte, line 109:

<comment>The blur event listener uses an anonymous function and is never removed in `onDestroy`, causing a listener leak on each HMR cycle. Extract the callback into a named function (like the other handlers) and add the corresponding `removeEventListener` in `onDestroy`.</comment>

<file context>
@@ -100,6 +105,8 @@
 		addEventListener("keydown", draggingKeyDown);
 		addEventListener("keydown", handleLayerPanelKeyDown);
+		addEventListener("keyup", draggingKeyUp);
+		addEventListener("blur", () => internalDragState?.active && abortDrag());
 
 		addEventListener("pointermove", clippingHover);
</file context>