fix(web): pasted CRLF text keeps its blank lines and caret in the composer

apps/web/src/components/ComposerPromptEditorTiptap.input.browser.test.tsx

@@ -362,6 +362,26 @@ it("keeps unknown dollar names editable when restoring and pasting a draft", asy
   expect(serializeEditorDoc(editor.state.doc).value).toBe(value);
 });
 
+it.each(["x\r\n\r\ny", "x\r\ry"])(
+  "pastes %j with the same blank line as x\\n\\ny",
+  async (text) => {
+    await using screen = await mountEditor("");
+    const { editor } = screen;
+    await act(async () => {
+      editor.commands.focus("end");
+      const clipboardData = new DataTransfer();
+      clipboardData.setData("text/plain", text);
+      editor.view.dom.dispatchEvent(
+        new ClipboardEvent("paste", { clipboardData, cancelable: true }),
+      );
+    });
+    const paragraphs: string[] = [];
+    editor.state.doc.forEach((node) => paragraphs.push(node.textContent));
+    expect(paragraphs).toEqual(["x", "", "y"]);
+    expect(serializeEditorDoc(editor.state.doc).value).toBe("x\n\ny");
+  },
+);
+
 it("keeps the caret inside unknown dollar text across rich and plain remounts", async () => {
   const value = "echo $HOME now";
   await using screen = await mountEditor(value);

apps/web/src/components/ComposerPromptEditorTiptap.tsx

@@ -131,7 +131,7 @@ import { Tooltip, TooltipPopup, TooltipTrigger } from "./ui/tooltip";
 import { ComposerCodeBlockNodeView } from "./chat/ComposerCodeBlockNodeView";
 import { resolveAssistantCitationCommentDismissal } from "./chat/assistantCitationCommentDismissal";
 import { composerCodeBlockHighlight } from "./composerCodeBlockHighlight";
-import { importPastedComposerText } from "./composerInlineTokenPaste";
+import { importPastedComposerText, readPastedPlainText } from "./composerInlineTokenPaste";
 import { didComposerSelectionChangeVisibly } from "./composerSelection";
 import type { ComposerDraftContextRecords } from "./composerContextPresentation";
 
@@ -1367,7 +1367,7 @@ function ComposerPromptEditorTiptapInner(
         handlePaste: (view, event) => {
           const clipboardData = event.clipboardData;
           if (!clipboardData || clipboardData.files.length > 0) return false;
-          const pastedText = clipboardData.getData("text/plain");
+          const pastedText = readPastedPlainText(clipboardData);
           if (!pastedText) return false;
           event.preventDefault();
           // Paste verbatim inside fences; markdown parsing would split blocks and create unsupported chips.

apps/web/src/components/composerInlineTokenPaste.test.ts

@@ -56,4 +56,10 @@ describe("importPastedComposerText", () => {
       pasted,
     );
   });
+
+  it("imports CRLF and CR clipboard text with LF line breaks", () => {
+    expect(
+      importPastedComposerText(clipboard({ "text/plain": "x\r\n\r\ny\rz" }), () => new Map()),
+    ).toBe("x\n\ny\nz");
+  });
 });

apps/web/src/components/composerInlineTokenPaste.ts

@@ -20,6 +20,11 @@ import { readThreadShell } from "~/state/entities";
 
 const threadTitle = (ref: ScopedThreadRef) => readThreadShell(ref)?.title;
 
+// Matches ProseMirror's default clipboard parser, which a custom handlePaste bypasses.
+export function readPastedPlainText(clipboardData: Pick<DataTransfer, "getData">): string {
+  return clipboardData.getData("text/plain").replace(/\r\n?/g, "\n");
+}
+
 /** Pasted thread links count as context too, so they become chips like a copied chip does. */
 export function readPastedComposerContext(
   clipboardData: Pick<DataTransfer, "getData">,
@@ -65,7 +70,7 @@ export function importPastedComposerText(
     fragment: ComposerContextClipboardFragment,
   ) => ReadonlyMap<string, string>,
 ): string {
-  const pastedText = clipboardData.getData("text/plain");
+  const pastedText = readPastedPlainText(clipboardData);
   const fragment = importContextFragment ? readPastedComposerContext(clipboardData) : null;
   const rewrittenIds =
     fragment && fragment.records.length > 0 ? importContextFragment!(fragment) : null;