#22231 cmux NEXT New Tab: paste and drop images and files, sent with the first prompt

Leo, 2026-10-19: "i cant paste in pictures in the new tab area but it works in the existing chats...?"

Cause

The New Tab page's prompt is its own <textarea> (newtab/NewTabScreen.tsx), not the chat composer (Composer.tsx). The chat composer's paste listener, document-level file drop (installFileDropLifecycle) and attachment chips all lived inside Composer, so on the New Tab page:

• a pasted image or copied file did nothing;
• a dropped file did nothing;
• even with a way to stage attachments, the page's first send (screenActions.onAsk → chat.send { text }) carried only text.

Fix

• The chat composer's attachment code moves to composer/attachmentIntake.tsx, and both composers use it:
  • useAttachmentIntake covers paste on the composer's field, file drop anywhere on the page, the moved-chat upload fallback and refusal notes.
  • AttachmentStrip / AttachmentChip / PdfAttachmentChip render the chips. They are moved, not changed.
  • Composer.tsx is 257 lines shorter.
• The New Tab page stages a pasted image, a copied file, a screenshot or a dropped file under the same chips, with the same remove and preview.
• onAsk passes the staged attachments. The chat's first chat.send carries { text, attachments }, and attachments alone are a prompt, as in a chat. A plain prompt sends exactly as before.

Tests

• test/new-tab-paste-attachments.test.ts (browser lane, Chromium + WebKit, the pane's dev entry as a New Tab page on the mock transport):
  • case 1: paste a PNG on the field → chip → Return → the chat's first message shows the text and the image (data:image/png);
  • case 2: drop a file on the page → chip → × removes it; a pasted image with no text → Return → the first message has the image.
  • All 4 cases fail at base dde0ebbee3 (no chip appears) and pass with the fix.
• test/new-tab-ask-attachments.test.ts: onAsk sends { text, attachments }, attachments alone, and a plain prompt unchanged. 2 of 3 fail at base.
• Chat composer regressions, on Huge Blue:
  • agent-pane-attach-typing (3/3) and agent-pane-sent-images (1/1) pass;
  • all new-tab-* and composer* jsdom tests pass (139/0);
  • lint, fmt and typecheck are clean.

The classic New Tab layout (NewTabPage, Debug Settings layout "a") is unchanged.

🤖 Generated with Claude Code

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Summary by cubic

Fixes the New Tab page so pasted or dropped images and files stage as chips and are sent with the first prompt, matching the chat composer.

• Moves the chat composer's attachment intake (paste, document-level drop, upload fallback, refusal notes) and its chips into composer/attachmentIntake.tsx, shared by Composer and the New Tab field.
• onAsk now passes staged attachments to the chat's first chat.send; attachments alone act as a prompt. Plain prompts send exactly as before, and the classic New Tab layout is unchanged.
• With attachments staged, Return starts a chat with the text and attachments instead of opening a suggested page, tab, or workspace; in shell mode a paste stays text.

Covered by browser tests (Chromium + WebKit) for paste and drop, and jsdom tests for onAsk sending attachments.