The whole headless-Chrome preview action is described in prompts and tool text, but its rendering module is absent so the action never joins the schema.
A new Artifact action would take a file_path, wrap that single page the way publishing does, render it in a headless Chrome over loopback and hand back JPEG screenshots at each requested width in both light and dark, along with a mechanical list of layout problems, all without uploading anything. In this build the rendering module itself is absent, so the internal availability accessor throws and the action text is never added to the tool schema, leaving it unreachable no matter how it is configured. Only the descriptions and prompt guidance that would tell the model about it actually ship.
- The missing module makes the internal accessor throw "artifact preview is not compiled into this build", and because the build-time constant behind it is null the gates are never consulted at all.
- Those gates, had they been reached, add the action to the tool schema when the
CLAUDE_CODE_ARTIFACT_PREVIEWenvironment variable is set or the server enables the flagtengu_cobalt_plinth_aspen, whose built-in fallback is false, and force it off whenCLAUDE_CODE_REMOTEis set. - Parameters are
widthsin CSS pixels, defaulting to 1280 and 390, andthemes, meaning light and dark. - The issue list would cover overflow, SVG clipping, theme-only CSS variables, blocked or local-only loads, mermaid diagram failures and console errors.
- Chrome is located by a bundled finder that is compiled in and has no other caller, using hardcoded per-platform paths including
/usr/bin/google-chrome-stable,/usr/bin/chromium-browser,Google Chrome.app/Contents/MacOS/Google Chromeandchrome.exeunder Program Files. - The action is classified read-only and safe to run concurrently, but it ignores whole-tool allow rules and suppresses always-allow prompting.
- A call made while the gate is shut returns "preview is not available in this session.", and the permission handler denies separately with "Preview gate closed at schema freeze".
- Telemetry event
tengu_artifact_previewwould record rendered, partial, failed and no_browser outcomes with counts of screenshots, issues, widths, themes, bytes and duration. - A stored preview result that has gone stale replies with an instruction to run the action again.
- This repeats the pattern of the Artifact rooms module that was already compiled out in 2.1.246; the preview half is new here.
Render a local page file in a headless browser to check it before publishing. Nothing is uploaded., Preview: action: "preview" with a file_path renders that one page file locally the way publish wraps it, in light and dark themes at desktop and phone widths, return V.CLAUDE_CODE_ARTIFACT_PREVIEW ?? we("tengu_cobalt_plinth_aspen", !1);, This record of a preview result is unreadable \u2014 re-run action: "preview" for a current render., For 'preview', the local .html page to render., artifact preview is not compiled into this build
Strings lifted out of the shipped bundle, so the claim above can be checked against them.
tengu_cobalt_plinth_aspen Not enough to sayNothing here resolved what this flag was doing on this version, so nothing here should be read as on or off.
This account: no value returned · anonymous baseline: no value returned · compiled default in v2.1.247: off
Read once, for one account on one subscription tier, against v2.1.247. It isn't a statement about your account. What a flag value here can and cannot tell you
New in this build: CLAUDE_CODE_ARTIFACT_PREVIEW