Claude iOS: template renders but host delivers no lifecycle notifications to MCP App iframes (tool-input, tool-result, size-changed all absent)

[bennewton999]

Environment: Claude iOS app (2026-07-30, Opus 5), remote MCP server via custom OAuth connector. Server: @modelcontextprotocol/ext-apps@1.7.5, @modelcontextprotocol/sdk@1.30.0, Streamable HTTP (stateless per-request). Tool registered with registerAppTool + _meta.ui.resourceUri; single-file HTML template with a version stamp in the footer so screenshots identify exactly which template version a host rendered.

Observed (4 instrumented live test rounds, template versions v1.2.0 → v1.4.0):

1. The ui:// template loads and renders — chrome, inputs, buttons, and our version stamp are all visible, so resource fetch + iframe mount work on iOS.
2. ui/notifications/tool-result is never delivered. The app registers ontoolresult before connect() per SDK guidance; the handler never fires. The same template receives it on Claude Desktop (when Desktop renders at all — see Bug Report: MCP Apps UI Resource Not Rendering in Claude Desktop / claude.ai #671).
3. ui/notifications/tool-input is never delivered either — instrumented separately from v1.3.0 onward.
4. ui/notifications/size-changed from the app is ignored — the iframe stays at a short initial height, clipping content (and McpUiResourceMeta offers no initial-size hint, so servers have no workaround).
5. iframe-initiated tools/call via callServerTool also appears non-functional in our v1.4.0 polling fallback, though we have less instrumentation certainty here than for 2–4.

Impact: any tool-result-driven interactive UI is non-functional on Claude iOS — the card renders as permanent chrome with no data and no working actions. We shipped a full accept/regenerate image-review card and had to park it. The workaround that works everywhere is putting next-step instructions in the tool result text and letting the model execute follow-ups conversationally.

Expected: per SEP-1865, the host delivers tool lifecycle notifications to the view after ui/initialize completes.

Repro: any registerAppTool sample whose ontoolresult handler displays received data — on iOS the handler never fires, while the same server renders end-to-end in the basic-host harness and MCPJam. Happy to share our server URL, template source, and timestamped screenshots on request.