#25190 Agent artifacts: render interactive HTML in the side preview

Leo: “the /side thing i heard somebody really liked in codex... and i think html/html artifacts and that kinda good viewing and good support for it would be cool”, and “like the claude.ai artifacts but imagien you didnt need to only have it on claude.ai...”.

This step extends the existing side-preview artifact surface (#19473/#19571/#24132) for provider-neutral interactive HTML/SVG/JSX artifacts. It keeps scripts inside an opaque sandboxed frame with no network, file, parent or remote-resource access by default, retains Open/Preview/Code/Copy/Save, and handles Claude, Codex, pi and Gemini full file writes through the normalized transcript model. Three revision gallery states and ten synthetic Chromium captures cover HTML, SVG, React hooks, JSX, writes and denied probes.

Red→green: 68de299107d69a3d0b3f05744a46ff60b2fee792 → 25d84ed996a99293ea541cfa7f791da1e1c1fc1b; after rebase onto feat-cmux-next the reviewed head is f05156799ba5522465ca9a6f711dbb525e16372e. Worker reports 7 focused artifact tests, 17 panel/Inspector tests, 27 gallery/environment tests, typecheck 2,579 files, changed-file lint/format, browser sandbox probes and no escaped network/file requests. Native WKWebView tests remain hosted work for the integration owner.

This does not touch Austin’s #8610 project artifact storage; it builds on the existing side preview.

Independent Codex gpt-6-astra xhigh review and exact-head hosted checks are required before landing.

Agent session: big-red

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