UAN-023 commercial agent hosts over remote MCP

Checked 2026-10-10 on macOS arm64 with Node 26.10.0. The server was the flagship E04 Worker sidecar on local workerd (Wrangler dev --local). It serves the shared E01 album contract over Streamable HTTP MCP at a loopback address. Each host ran from a temporary working directory under the operator's existing sign-in. No credential was added for this test.

Antigravity CLI: tool invocation verified

The Antigravity CLI (agy, Google) ran with model gemini-3.8-flash-low. Its HTTP MCP server entry was added for the test with agy mcp add and removed afterwards.

Run	Host version	Observation
Manual	1.2.14	Host listed `cap_15_example.catalog_12_album.lookup_v1`, called it through `call_mcp_tool` with `{"slug":"first-light"}`, received `{"result":{"kind":"found",…}}` and answered `First Light`
`node test/uan023-agent-host.mjs agy`	1.3.3 (auto-updated)	Same found call and answer. A second prompt sent the invalid slug `Not A Slug!` unchanged; the tool returned an error and no album

Claude Code: tool invocation verified

Claude Code 2.1.286 ran with an isolated --mcp-config and --strict-mcp-config, the tool allowlist limited to the probe server, and model haiku.

Connection: an earlier attempt that day reported the server connected and exposed exactly one tool, mcp__albums__cap_15_example_catalog_12_album_lookup_v1. That tool name is Claude Code's own sanitized projection. That attempt stopped before any model turn because the standalone CLI sign-in had expired.
Invocation: with the operator's Claude OAuth token supplied through CLAUDE_CODE_OAUTH_TOKEN, node test/uan023-agent-host.mjs claude passed. The host called the tool with {"slug":"first-light"} and answered First Light. The unchanged invalid slug Not A Slug! returned a tool result with is_error: true and no album.

Reproduce

npm ci
npm run example:e04
node test/uan023-agent-host.mjs agy
CLAUDE_MODEL=haiku node test/uan023-agent-host.mjs claude

The script starts the sidecar on a free loopback port. For Antigravity it registers a temporary uan-albums-probe MCP server, runs the two prompts, asserts the actual tool calls from the host's stream-json events, and always removes the server and stops the Worker. It uses model inference on the operator's account, so it is not part of npm run check.

Limits

Each host version was observed once on one machine. Host model behavior may vary between runs.
The server ran on loopback. No deployed sidecar, external identity provider or protected capability was used.
MCP Apps UI rendering in these hosts was not tested; the rendered MCP Apps host evidence remains the Inspector run.