[frenchie4111]

Tool-result screenshots already showed up in the transcript as thumbnails on the tool card (#303, #314), but an agent had no way to put one in its own prose — which is where "here's the thing I just built" belongs.

Getting the screenshot into the reply

The agent never learned where the capture landed. The MCP result is image bytes, and the path Ness spills them to was derived later, in the transcript extractor. /browser/screenshot now does the spill itself and returns the path; the bridge appends one terse line to the result. The write is content-hash keyed, so it's the same file the extractor derives from the image block — one copy, not two.

A local path in markdown couldn't render anyway. The renderer's origin is app:// (http://localhost in dev), so an absolute filesystem path resolves against the wrong root, and react-markdown blanks file:// in its default URL transform. Chat markdown now routes srcs that look like local files through the attachment-read IPC the existing thumbnails already use. Works for any image on the machine, not just screenshot_tab captures. Remote srcs keep their old behaviour, and a blanked javascript: src renders nothing.

Sizing

CommonMark has no sizing syntax and raw HTML is off in chat (rehype-raw would let any model-authored markup into the renderer), so the size rides in the places an image already carries free text. Three forms, all prior art, because agents guess differently:

form	example
pipe in the alt (Obsidian)	
leading-= title (markdown-it-imsize)	
fragment on the path	

Specs are 400, 400x300, x300, 50%, clamped to 16–2000px. A title without the = is still a tooltip; alt text that merely contains a pipe is left whole.

The fragment form is why this isn't just the first two: it previously resolved to nothing and fell through to a broken <img> that rendered as blank space — the worst outcome for someone who guessed a reasonable syntax.

Unsized default is 16rem tall / 32rem wide (was 24rem tall), since one screenshot was taking about a third of the chat window.

Still renders as raw text: ![](path =200x) with the spec outside the quotes. CommonMark won't parse it as an image at all, so honouring it needs a remark transform — skipped as out of proportion to three working forms.

Verification

• src/shared/chat-image-src.test.ts — 22 cases over src resolution (posix, file:// + percent-decode, drive letters, remote/relative/unknown-ext rejections) and the three size parsers (clamping, non-size tails, tooltip preservation).
• New control-server test pins the returned path shape and that a repeat capture of the same bytes reuses the file.
• react-markdown wiring confirmed in node via renderToStaticMarkup: absolute paths, file://, alt pipes and = titles all arrive intact — including a pipe escaped inside a GFM table cell; javascript:alert(1) arrives blanked and renders nothing.
• Visual, against a live transcript in the web client: the title and fragment forms both render at the requested 200px, and the unsized control dropped from ~535×340 to ~357×218.
• npm run typecheck, npx electron-vite build, and all 1745 tests pass.

🤖 Generated with Claude Code