Attach dropped files in every composer (#1750)

* fix(app): attach dropped files in composer

Composer parents had to expose attachment callbacks, so New Workspace only wired image drops and JSON files never became file attachments. Centralize dropped-file ingestion in Composer so all composer surfaces share the same image and file path.

* fix(app): handle desktop dropped attachment paths

packages/app/e2e/composer-attachments.spec.ts

@@ -16,6 +16,7 @@ import {
   expectComposerEditable,
   expectAttachButtonDisabled,
   fillComposerDraft,
+  dropFileOnComposer,
   sendDraftToQueue,
   expectQueuedMessageButton,
   startRunningMockAgent,
@@ -36,6 +37,11 @@ const MINIMAL_PNG = Buffer.from(
 );
 
 const TEST_IMAGE = { name: "test.png", mimeType: "image/png", buffer: MINIMAL_PNG };
+const TEST_JSON = {
+  name: "config.json",
+  mimeType: "application/json",
+  buffer: Buffer.from(JSON.stringify({ composer: "drop" })),
+};
 
 test.describe("Composer attachments", () => {
   test("Plus menu shows image and GitHub options", async ({ page, withWorkspace }) => {
@@ -172,6 +178,47 @@ test.describe("Composer attachments", () => {
     await expectAttachmentPill(page, "composer-image-attachment-pill");
   });
 
+  test("dropped JSON file renders as a file attachment in active chat", async ({
+    page,
+    withWorkspace,
+  }) => {
+    test.setTimeout(60_000);
+    const workspace = await withWorkspace({ prefix: "attach-drop-json-" });
+    await workspace.navigateTo();
+    await clickNewChat(page);
+    await expectComposerVisible(page);
+
+    await dropFileOnComposer(page, TEST_JSON);
+
+    await expectAttachmentPill(page, "composer-file-attachment-pill");
+  });
+
+  test("dropped JSON file renders as a file attachment in New Workspace", async ({ page }) => {
+    test.setTimeout(120_000);
+    const workspace = await seedWorkspace({ repoPrefix: "attach-drop-new-workspace-" });
+
+    try {
+      await gotoAppShell(page);
+      await waitForSidebarHydration(page);
+      await switchWorkspaceViaSidebar({
+        page,
+        serverId: getServerId(),
+        workspaceId: workspace.workspaceId,
+      });
+
+      await openNewWorkspaceComposer(page, {
+        projectKey: workspace.projectId,
+        projectDisplayName: workspace.projectDisplayName,
+      });
+
+      await dropFileOnComposer(page, TEST_JSON);
+
+      await expectAttachmentPill(page, "composer-file-attachment-pill");
+    } finally {
+      await workspace.cleanup();
+    }
+  });
+
   test("clicking the X on an image pill removes it", async ({ page, withWorkspace }) => {
     test.setTimeout(60_000);
     const workspace = await withWorkspace({ prefix: "attach-remove-" });

packages/app/e2e/helpers/composer.ts

@@ -95,6 +95,33 @@ export async function expectAttachmentPill(page: Page, testID: string): Promise<
   await expect(page.getByTestId(testID).first()).toBeVisible({ timeout: 10_000 });
 }
 
+export async function dropFileOnComposer(
+  page: Page,
+  file: { name: string; mimeType: string; buffer: Buffer },
+): Promise<void> {
+  const dataTransfer = await page.evaluateHandle(
+    ({ name, mimeType, base64 }) => {
+      const bytes = Uint8Array.from(atob(base64), (char) => char.charCodeAt(0));
+      const droppedFile = new File([bytes], name, { type: mimeType });
+      const transfer = new DataTransfer();
+      transfer.items.add(droppedFile);
+      return transfer;
+    },
+    {
+      name: file.name,
+      mimeType: file.mimeType,
+      base64: file.buffer.toString("base64"),
+    },
+  );
+
+  const composerRoot = page.getByTestId("message-input-root").filter({ visible: true }).first();
+  await expect(composerRoot).toBeVisible({ timeout: 10_000 });
+  await composerRoot.dispatchEvent("dragenter", { dataTransfer });
+  await composerRoot.dispatchEvent("dragover", { dataTransfer });
+  await composerRoot.dispatchEvent("drop", { dataTransfer });
+  await dataTransfer.dispose();
+}
+
 /** Hover to reveal the X button (hidden until hover on desktop web), then click by accessible label. */
 export async function removeAttachmentPill(
   page: Page,