[Bug]: MCP App inline frames never go below 80px, so compact apps get blank space under them #35911

Before submitting#

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

Area#

apps/web

Steps to reproduce#

1. Connect an MCP server whose tool declares an MCP App (_meta.ui.resourceUri → text/html;profile=mcp-app).
2. Make the app render a compact single-row view (for example a one-line "receipt" of the tool call, about 40–50px tall) and report it after ui/notifications/initialized:

   { "jsonrpc": "2.0", "method": "ui/notifications/size-changed", "params": { "height": 48 } }

3. Have the agent call the tool a few times in a row so several app cards stack in the timeline.

Expected behavior#

The inline iframe follows the height the app reports (48px here), so a series of one-line cards stacks tightly, like normal tool-call rows.

Actual behavior#

Every inline iframe is at least 80px tall. The app's content sits at the top and the rest stays blank, so each card carries roughly 30–40px of empty space under it and a run of tool calls is spread far apart.

The floor comes from clampMcpAppHeight in packages/shared/src/mcpApp.ts:

const MCP_APP_MIN_HEIGHT = 80;
export const MCP_APP_DEFAULT_HEIGHT = 320;

export function clampMcpAppHeight(height: number): number {
  if (!Number.isFinite(height)) return MCP_APP_DEFAULT_HEIGHT;
  return Math.round(Math.min(MCP_APP_MAX_HEIGHT, Math.max(MCP_APP_MIN_HEIGHT, height)));
}

McpAppFrame.tsx applies it to every size-changed (setHeight(clampMcpAppHeight(size.height))), and mobile's mcpAppInlineHeight uses the same clamp. The app has no way to get below 80px; centering the content in the frame only moves the blank space around.

A floor makes sense before the app has reported anything (the 320px default covers that). Once an app has measured itself, a small floor (or none beyond a positive height) would let compact apps render at their real size.

Impact#

Cosmetic issue

Version or commit#

Desktop 0.1.9; source checked at main @ 6f108e8

Environment#

macOS, T3 Code desktop app 0.1.9

Workaround#

None on the app side. Apps can only make their content at least 80px tall to fill the frame.