html_render frames: the enlarged view loads a second instance, so page state and ui/message do not carry between the inline frame and the enlarged one #36295

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/desktop

Steps to reproduce

A page shown with html_render (an HTML drawing board that keeps its state in memory and, on a Send button, posts a ui/message request to window.parent) behaves as two separate pages once the enlarged view is used.

1. Render a page whose state lives in memory and whose button runs window.parent.postMessage({ jsonrpc: "2.0", id: "x", method: "ui/message", params: { role: "user", content: [{ type: "text", text: "..." }] } }, "*").
2. Draw inline and press Send: the text arrives in the thread as the next user message. This works.
3. Give the frame a height of about 1000 px: the enlarged view option appears (the option is not offered for a 620 px frame; this threshold is an observation, not verified).
4. Open the enlarged view: the page starts empty, so it is a second instance, not the same frame moved.
5. Draw in the enlarged view and press Send: no message reaches the thread.
6. Close the enlarged view: the inline frame still shows what it showed before; everything drawn in the enlarged view is gone.

Expected behavior

One of: the same frame is moved into the enlarged view and back, so state is kept; or the enlarged frame's ui/message is accepted too; ideally both.

Actual behavior

The enlarged view loads a second instance of the page. Its state is separate from the inline frame, and its ui/message is not delivered to the thread.

Also observed:

• localStorage writes and storage events did not make the two instances share a drawing, which suggests each frame has its own isolated storage.

Impact

Major degradation or frequent failure

Version or commit

Not looked up.

Environment

T3 Code desktop app on macOS, Claude Code provider, 2026-11-13. (I did not look up the exact app version.)

Workaround

Copy the text to the clipboard on Send, then paste it into the composer by hand. It works but breaks the flow.