[Feature]: Render HTML files in the web file preview

[tastelessjolt]

Before submitting

• I searched existing issues and did not find a duplicate.
• I am describing a concrete problem or use case, not just a vague idea.

Area

apps/web

Problem or use case

Opening an HTML file from the workspace file viewer shows its source. The action that opens previewable files in the integrated browser is only available in the desktop runtime, so users of the served web app cannot see the rendered result from the file panel.

Proposed solution

For HTML files, offer a Rendered view alongside the existing Source view. Render the document in a sandboxed iframe without same-origin access. The source view should remain available for inspection and editing workflows.

A first implementation could use srcdoc for self-contained HTML documents. Broader support for referenced workspace assets can be considered separately if it requires URL rewriting or additional server behavior.

Why this matters

Users frequently ask agents to produce small HTML artifacts, reports, and prototypes. Seeing the rendered output directly in the file viewer would make those outputs useful on the web surface without requiring the Electron-only browser preview.

Smallest useful scope

Support .html and .htm files in the web file panel with:

• Source and Rendered modes
• A sandboxed iframe for Rendered mode
• No same-origin permission, popups, top-level navigation, or downloads
• Self-contained HTML only; relative workspace assets do not need to work initially

Alternatives considered

• Open the file in the integrated browser. This works in the desktop app but is unavailable in served web.
• Always render HTML. Keeping the source view avoids losing the current file-inspection behavior.
• Add a general server preview gateway first. That would solve a broader problem but is substantially larger than rendering a single HTML artifact.

Risks or tradeoffs

HTML may contain scripts or expensive content, so iframe sandboxing and lifecycle cleanup are important. CSP behavior, iframe navigation, large documents, and whether scripts should be enabled need an explicit decision. Supporting relative assets later may require signed URLs or safe URL rewriting.

Examples or references

• Support File Explorer and File Preview #763 contains an earlier comment proposing a rendered HTML iframe, but the issue was closed when the general file viewer shipped.
• Add workspace file browser and preview panel #3087 added the current workspace file browser and preview panel.
• fix(web): preview workspace images in the file panel #3996 added direct workspace image previews for web and remote environments where the integrated browser is unavailable.
• Add archived threads and mobile file viewer #3155 includes HTML WebView preview on mobile.

Contribution

• I would be open to helping implement this.