mirror of
https://github.com/CopilotKit/CopilotKit.git
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Ben Taylor
478a2aac95
## What
The MCP Apps example widgets report their intrinsic size with
`ui/notifications/size-change`, but both the host and the ext-apps spec
use
`ui/notifications/size-changed`:
- Host: `MCPAppsActivityRenderer` only handles `case
"ui/notifications/size-changed"` and
reads `{ width, height }` from it to size the iframe.
- Spec: `@modelcontextprotocol/ext-apps` defines
`McpUiSizeChangedNotification` with
`method: "ui/notifications/size-changed"` (`App.sendSizeChanged`).
Because the names differ by one letter, the host never receives the size
and the widget
iframe stays at its initial height instead of growing to fit its
content.
## Fix
Rename the notification to the spec name in the affected widgets. The
payload is unchanged
(`{ width, height }`), which is exactly what the host reads, so this is
a one-line change per
widget on the sender side only.
No host change: in JSON-RPC a notification (no `id`) must not be
answered, so the host
silently ignoring the old name is correct behavior; the bug is purely
that the widgets sent
the wrong method name.
## Affected widgets
- `examples/showcases/mcp-apps/mcp-server/apps`: flights, hotels,
kanban, trading
- `examples/showcases/generative-ui-playground/mcp-server/apps`:
calculator, flights, hotels,
kanban, todo, trading
## Testing
Reproduced against a local run of `examples/showcases/mcp-apps` (Next
frontend + MCP server):
before, the widget iframe rendered at its initial height; after the
rename the host receives
`size-changed` and the iframe resizes to the widget content.
## A note from the contributors
From the team at MCP Apps Builders - part of our ongoing series to round
out MCP Apps host
support in CopilotKit. Opening as a draft for review.