[FEATURE]: Paste images into built-in questions tool answer #24199

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Describe the enhancement you want to request

Summary

When an agent calls the built-in question / ask-user tool and the user replies, let the user paste an image from the clipboard into the answer box. The tool should persist the pasted image to a temp file and return its absolute path as part of the user's answer, so the agent can immediately consume it (e.g. re-read with its Read tool, pass to vision, attach to a follow-up message).

Motivation

Agents frequently need to collect visual context mid-run — screenshots of bugs, design mocks, stack-trace pictures, diagrams. Today the only way to get an image to the agent during a question reply is:

1. Save the clipboard image to disk manually
2. Paste/type the absolute path as text

This breaks flow and is error-prone (wrong path, forgotten save step). Interactive MCP desktop apps (e.g. interactive-mcp-server's QuestionDock) already solve this by intercepting paste, saving clipboard bytes to a temp location, and inlining the absolute path into the answer. The built-in tool should match that UX.

Proposed behavior

• While typing an answer to a question prompt, pressing paste (⌘V / Ctrl+V) with an image on the clipboard:
  1. Writes the image bytes to a temp file (e.g. $TMPDIR/opencode-clipboard-<timestamp>.<ext>).
  2. Inserts the absolute path as text at the caret, optionally wrapped (e.g. file:///... or plain path).
  3. Returns that path in the tool response answer field alongside any other text the user typed.
• Supported formats: PNG, JPEG, WebP, GIF (at minimum PNG — the common clipboard format).
• No change when clipboard contains plain text.
• Multiple images in one answer should each produce their own absolute path.

Why the path (not base64)

• Agent's existing Read / vision tools already take paths.
• Keeps the question response small.
• Matches how screenshots, file-drag, and @file mentions already work.

Prior art

• GitHub/Slack/Discord clipboard-image-paste flows.

Acceptance criteria

• User can paste an image while answering a question prompt.
• Image is saved to a temp file; absolute path returned to agent in the answer.
• Plain-text paste still works unchanged.
• Works on macOS, Linux, Windows.
• Temp files are cleaned up per OS temp-dir policy (no long-lived growth).