Fix optimistic comment draft clearing

ui/src/lib/comment-submit-draft.test.ts

@@ -0,0 +1,31 @@
+import { describe, expect, it } from "vitest";
+import { restoreSubmittedCommentDraft } from "./comment-submit-draft";
+
+describe("restoreSubmittedCommentDraft", () => {
+  it("restores the submitted body when the editor is still empty after a failed request", () => {
+    expect(
+      restoreSubmittedCommentDraft({
+        currentBody: "",
+        submittedBody: "Retry me",
+      }),
+    ).toBe("Retry me");
+  });
+
+  it("treats whitespace-only input as empty when restoring a failed draft", () => {
+    expect(
+      restoreSubmittedCommentDraft({
+        currentBody: "   ",
+        submittedBody: "Retry me",
+      }),
+    ).toBe("Retry me");
+  });
+
+  it("preserves newer input when the user has already typed again", () => {
+    expect(
+      restoreSubmittedCommentDraft({
+        currentBody: "new draft",
+        submittedBody: "Retry me",
+      }),
+    ).toBe("new draft");
+  });
+});