Plugin pane buttons dropped when the desktop surface renders the same pane at two widths (ui_press handled: false)

Plugin pane buttons stop working when the desktop surface renders the same pane at two widths

Version: Claude Code 2.1.296, Claude desktop app (Code tab), macOS (Darwin 27.0.0)
Plugin: agents-panel 0.5.0 (a mod that draws a Pane with Button elements, each with a key)

What happens

In the desktop app, clicking buttons in a plugin's pane often does nothing. In our case the pane's ▶ buttons start agents, and the click is simply dropped: no run is recorded. I also see "unable to do task" errors after some launches, but have not tied that message to this cause.

Cause (reproduced headlessly)

When a surface renders the same Pane instance twice at different bodyColumns, the second ui_render gives its buttons new press handles and releases the handles from the first render. A ui_press that uses a handle from the first render comes back {handled: false}. The desktop app does draw the pane twice at different widths, so any press that lands on the first drawing is dropped.

This happens with one client_id drawing twice and with two different client_ids.

Repro

ui_render the same pane (component: 'Pane', instance_id: 'agents-panel', surface: 'desktop') at bodyColumns: 60, then at bodyColumns: 44, and then ui_press each button's handle:

same client, two widths    | A handle 180981019  B handle 180981045
   A presses its button: {'handled': False}
   B presses its button: {'handled': True, 'element': 'fold:self'}
two clients, two widths    | A handle 180981071  B handle 180981097
   A presses its button: {'handled': False}
   B presses its button: {'handled': True, 'element': 'fold:self'}

Pressing with a fresh render's handle always works. Only the older render's handle is dropped.

Expected

Pressing a button from either drawing of the pane is handled, or the app never keeps a drawing whose handles have been released.

Notes

• The plugin cannot fix this. It never sees the dropped press, because the engine answers handled: false before any hook runs.
• The plugin's session file (~/.claude/agents-panel/sessions/<id>.json) shows runs: [] after a click, so the press never reaches the plugin.