fix: persist clipboard images as temp files with file:// URLs

[dorukardahan]

Issue for this PR

Closes #14673

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

When an image is pasted from clipboard, OpenCode stored it as an inline data:image/...;base64,... URL. MCP tools (look_at, understand_image) expect a file path on disk, not a base64 string, so they couldn't analyze pasted images.

This PR:

1. Saves clipboard images to temp files (os.tmpdir()/opencode-clipboard-<timestamp>.png) and keeps the file path
2. Uses file:// URLs so MCP tools can access the file
3. Converts file:// back to data: URLs before sending to AI SDK (which rejects file:// scheme)

Changes:

• clipboard.ts — save temp file, return filepath in Content, unique filenames with timestamp
• prompt/index.tsx — pass filepath through attachment flow, use file:// URL when filepath exists
• prompt.ts — use part.url directly instead of re-reading the file
• message-v2.ts — convert file:// → data: before AI SDK consumption (in both user message parts and tool output attachments)

How did you verify your code works?

• All 23 message-v2 tests pass
• All 45 prompt-related tests pass
• tsgo --noEmit typecheck passes
• CI: typecheck pass, unit (linux) pass, unit (windows) pass

Screenshots / recordings

No UI changes — purely internal data handling.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

Note: There is an open PR #21633 addressing the same issue. This PR takes a more complete approach by also handling file:// → data: conversion in message-v2.ts (both user parts and tool output attachments), ensuring the AI SDK never sees a file:// URL it would reject.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Potential Duplicate Found

PR #21633: fix(tui): save clipboard-pasted images to temp files for MCP tool access

Reason: This PR appears to be addressing the same issue as PR #22218. Both are focused on saving clipboard-pasted images to temp files for MCP tool access. PR #21633 specifically mentions the same core functionality of persisting clipboard images for MCP tools.

[github-actions]

Thanks for updating your PR! It now meets our contributing guidelines. 👍

[dorukardahan]

Pushed an update: added error handling for the file:// → data: URL conversion in both locations (async path and sync callback). If a temp file has been deleted before conversion, it falls back to a text placeholder instead of crashing the message pipeline. All tests pass.