fix(chat-ui): support pasting image attachments

[janburzinski]

Summary

• handle pasted clipboard images in the shared chat composer
• route pasted images through the existing ACP attachment upload flow for every supported agent
• prefer one supported clipboard representation to avoid duplicate TIFF/PNG uploads on macOS

Root cause

The shared chat composer only handled drag-and-drop events, so Cmd+V image data never entered the existing attachment pipeline.

Screen recording

https://cap.link/1k3av3k59dbpst0

[greptile-apps]

Greptile Summary

This PR adds pasted image support to the shared chat composer. The main changes are:

• Image files from clipboard paste events are collected and routed through the attachment flow.
• Mixed text-and-image pastes keep normal text insertion while adding image attachments.
• ACP image uploads now filter unsupported formats and show a toast for rejected files.
• Supported ACP image MIME types can be inferred from common file extensions.

Confidence Score: 5/5

This looks safe to merge.

• No blocking issues found in the changed code.

Important Files Changed

Filename	Overview
packages/ui/src/react/components/chat-composer/index.tsx	Adds paste-time image detection and routes pasted image files through the existing attachment callbacks.
apps/emdash-desktop/src/renderer/features/conversations/acp/acp-chat-panel.tsx	Adds ACP image format filtering, extension-based MIME inference, and user-facing feedback for unsupported pasted images.

_{Reviews (9): Last reviewed commit: "fix(chat): handle generic clipboard imag..." | Re-trigger Greptile}

[janburzinski]

@greptileai

[janburzinski]

@greptileai

[janburzinski]

@greptileai

[janburzinski]

@greptileai

[janburzinski]

@greptileai

[janburzinski]

@greptileai

[janburzinski]

Cleaned this up to keep the PR focused on ENG-1852. Pasted images now just use the existing attachment flow, so we don’t need the extra helpers or API changes.

[janburzinski]

@greptileai

[arnestrickmann]

lgtm - manually tested it - works!