fix(signals): preserve sibling queues during traversal

.changeset/fix-scheduler-child-queue-removal.md

@@ -0,0 +1,5 @@
+---
+"@solidjs/signals": patch
+---
+
+Keep traversing sibling effect queues when a child queue removes itself or an earlier sibling during a flush. Previously, the shifted sibling could be skipped and leave its queued effects unexecuted.

packages/solid-signals/src/core/scheduler.ts

@@ -295,7 +295,12 @@ export class Queue implements IQueue {
       this._queues[type - 1] = [];
       runQueue(effects, type);
     }
-    for (let i = 0; i < this._children.length; i++) (this._children[i] as any).run?.(type);
+    for (let i = 0; i < this._children.length; ) {
+      const child = this._children[i];
+      (child as any).run?.(type);
+      // A child may remove itself or an earlier sibling while its effects run.
+      if (this._children[i] === child) i++;
+    }
   }
   enqueue(type: number, fn: QueueCallback): void {
     if (type) {

packages/solid-signals/tests/scheduler-livelock.test.ts

@@ -1,6 +1,7 @@
 import { expect, it } from "vitest";
 import {
   createEffect,
+  createLoadingBoundary,
   createMemo,
   createRenderEffect,
   createRoot,
@@ -187,3 +188,47 @@ it("isPending(() => latest(x)) in a user effect does not loop on refetch (#2843)
   dispose();
   flush();
 });
+
+it("disposing the current boundary queue does not skip its sibling", () => {
+  const effects: string[] = [];
+  const disposers: (() => void)[] = [];
+
+  try {
+    createRoot(dispose => {
+      disposers.push(dispose);
+      createLoadingBoundary(
+        () => {
+          createEffect(
+            () => undefined,
+            () => {
+              effects.push("first");
+              dispose();
+            }
+          );
+        },
+        () => undefined
+      )();
+    });
+
+    createRoot(dispose => {
+      disposers.push(dispose);
+      createLoadingBoundary(
+        () => {
+          createEffect(
+            () => undefined,
+            () => {
+              effects.push("second");
+            }
+          );
+        },
+        () => undefined
+      )();
+    });
+
+    flush();
+    expect(effects).toEqual(["first", "second"]);
+  } finally {
+    for (const dispose of disposers) dispose();
+    flush();
+  }
+});