Apps tab — AppRenderer with imperative ref #1262

Context

The AppRenderer is the heaviest piece of the Apps tab — it owns the iframe and the AppBridge lifecycle from @modelcontextprotocol/ext-apps. To keep the screen layer "dumb", the wiring layer (Phase 3) constructs the bridge from the active MCP Client and pushes input/result/cancellation through an imperative ref rather than via prop drilling.

See Apps Screen feature spec and storybook component plan entry 2.5b.

Legacy v1 reference: AppRenderer.tsx.

Scope

AppRenderer

• Path: clients/web/src/components/elements/AppRenderer/ (or groups/ if it ends up composing other parts).
• Props:
  • sandboxPath: string — URL/path of the sandbox proxy iframe.
  • tool: Tool — selected app tool (used for resource URI lookup).
  • bridgeFactory: (iframe: HTMLIFrameElement) => AppBridge — wiring layer constructs the bridge using a real MCP Client.
  • onError?: (err: Error) => void — error notifications.
• Imperative ref (AppRendererHandle):
  • sendToolInput(args: Record<string, unknown>): Promise<void>
  • sendToolResult(result: CallToolResult): Promise<void>
  • sendToolCancelled(reason: string): Promise<void>
  • teardown(): Promise<void>
• Owns the iframe element and AppBridge handle; no Mantine controls beyond a positioning Box.
• On unmount: invokes bridge.teardownResource(...) then disconnects the transport.

Stories

• Loading (iframe mounting), Loaded (with mock bridge factory), Error, Maximized.
• Mock the bridge factory in stories so Storybook does not need a real MCP client.

Acceptance criteria

• Real MCP types only (Tool, CallToolResult, Implementation) — no v1.5 wrappers.
• Bridge construction is delegated entirely to bridgeFactory so the renderer is testable in Storybook with mocks.
• No store access; no business logic — only iframe + bridge proxy.
• Tests pass and coverage is ≥ 90%.
• Cleans up the bridge on unmount (no leaked MessagePort listeners).

Dependencies

• Blocked by: Apps tab — add @modelcontextprotocol/ext-apps dep and isAppTool helper in core.
• Can run in parallel with: AppListItem/AppDetailPanel issue.

Branch / Base

• Base: v2/main
• Label: v2