[Bug]: Assistant Markdown image links do not resolve relative to the workspace in chat

[Horizonll]

Summary

When an assistant response includes a Markdown image with a relative path, such as ![ReLU 图像](relu.png), the chat renderer does not reliably resolve the image against the active workspace.

The expected behavior is for the image to load from the current session workspace, so images generated by the agent can be previewed inline in chat.

Area

Web UI

Reproduction or evidence

1. Open a workspace in BitFun.
2. Have the agent generate or save an image file in the workspace, for example relu.png.
3. Have the assistant respond with Markdown: ![ReLU 图像](relu.png).
4. Observe that the image is not reliably displayed inline because the relative image path is not anchored to the active session workspace.

Expected: relu.png resolves relative to the active session workspace and renders inline in the chat message.

Environment, if relevant

No response