feat(app): migrate to solid-sonner (#39519)

Co-authored-by: Brendan Allan <git@brendonovich.dev>

packages/app/test-browser/toast-owner.test.ts

@@ -1,8 +1,46 @@
-import { describe, expect, test } from "bun:test"
+import { beforeEach, describe, expect, test } from "bun:test"
 import { createSignal, type JSX } from "solid-js"
 import { showToastV2, toasterV2 } from "@opencode-ai/ui/v2/toast-v2"
 
 describe("showToastV2", () => {
+  // The toast registry is module state, so each test starts from an empty stack.
+  beforeEach(() => {
+    toasterV2.dismiss()
+  })
+
+  test("coalesces exact active content", () => {
+    const first = showToastV2({ title: "Repeated error", description: "Try again" })
+    const second = showToastV2({ title: "Repeated error", description: "Try again" })
+    const different = showToastV2({ title: "Repeated error", description: "A different error" })
+
+    expect(second).toBe(first)
+    expect(different).not.toBe(first)
+
+    toasterV2.dismiss(first)
+    toasterV2.dismiss(different)
+  })
+
+  test("allows dismissed content to appear again", () => {
+    const first = showToastV2("Dismiss and retry")
+    toasterV2.dismiss(first)
+
+    const second = showToastV2("Dismiss and retry")
+    expect(second).not.toBe(first)
+
+    toasterV2.dismiss(second)
+  })
+
+  test("recreates matching content when it is not the topmost toast", () => {
+    const first = showToastV2("First toast")
+    const topmost = showToastV2("Topmost toast")
+    const repeated = showToastV2("First toast")
+
+    expect(repeated).not.toBe(first)
+
+    toasterV2.dismiss(topmost)
+    toasterV2.dismiss(repeated)
+  })
+
   test("creates no reactive computations at call time", () => {
     const [tick, setTick] = createSignal(0)
     let reads = 0