Chat: local Markdown images in answers still render as file links #2434

Problem

• Local Markdown images in agent answers render as ! followed by a file link instead of an inline image.
• For example, ![Diagram](./out/diagram.png) shows a clickable label, although the same image renders in the Markdown file viewer.
• This affects answer text, independently of user attachments and tool-result image blocks.
• The problem is reproducible in v0.4.20, and the missing Chat context is still present on main at 1a0e441f.
• Chat: show images agents read or produce inline for pi, omp, Claude Code and Codex #992 included this as its fifth proposed change. The native transcript-image work addressed other carriers; this answer-Markdown path appears to remain incomplete.

Reproduction

1. Use an agent pane whose working directory contains out/diagram.png.
2. Have an answer contain ![Diagram](./out/diagram.png).
3. Open the pane in Chat.
4. Observe ! plus a file link instead of the picture.

Expected behavior

• Show supported local Markdown images inline, as the Codex app does in the reported workflow.
• Resolve relative paths against the pane's cwd, and absolute paths / local file:// URIs directly.
• Keep unresolved or external references as links, and retain the existing image-size limit.

Diagnosis and proposed fix

• Markdown.tsx already has MarkdownImageContext and an asynchronous image renderer.
• FileViewer.tsx provides its resolver, but ChatView.tsx does not. With a null context the renderer deliberately uses the link fallback.
• Supply Chat with the existing markdownImagePreview resolver through useMachineApi, including the pane ID for stat and file URLs.
• Reuse stat-before-load, the 20 MiB inline limit, oversized-image download links, and the existing reserved image layout. No new endpoint or CSP change is needed.
• A local patch using this approach successfully rendered two PNGs in an existing conversation. A focused PR will include regression coverage.

Environment

• macOS, Apple Silicon
• Ovis v0.4.20; source also checked against main at 1a0e441f
• Codex conversation containing local Markdown image references

Pull request

• Proposed fix and regression coverage: fix(chat): render local Markdown images inline #2435.