2026-11-03 — The stateless era and MCP tasks, smoke-tested against Claude Code

The §11 design (session as a create-session handle, the tool list following each request's tasks declaration, a 10 s grace before an eval answers as a task) built as a spike and run against claude-code 2.1.317 through bb dev, with a temporary request log in the transport. One conversation, one session (bfw).

The client is modern and declares tasks everywhere. It opens with server/discover — no initialize — then tools/list, and every request, tools/list included, carries io.modelcontextprotocol/tasks under _meta.clientCapabilities.extensions, beside roots and elicitation. So the reduced list (create-session, eval without await) is what it got, and the varying list is decidable from the listing request alone. Tool calls also carry a claudecode/toolUseId in _meta.

What the model sees when a call becomes a task is the client's own text, not the server's: "started server-side task bfw-2 … moved to the background as task k71c3shcl … use TaskStop with task_id …". The statusMessage never reached the model. The registry bridge survives anyway, by the task id's shape: bfw-2 names entry 2, so (res 2) is one inference away. The notification on settling carried the full rendering — value, ;; out, footer — and the entry was delivered through it (touched, told), never appearing as ;; settled news.

Polling honours pollIntervalMs: 16 tasks/get for a 25 s eval, gaps 1002–1030 ms against the advertised 1000.

TaskStop sends tasks/cancel — twice, for one stop; idempotent here. The entry settled :cancelled; no notification followed.

A failure after the grace arrives as a failed task notification ("Task failed: …") with the rendering and footer — but flattened to one line, where a completed result keeps its newlines. Readable, and the frames survive, but a multi-line error rendering loses its shape on this path.

A refused handle mints nothing: eval with zzz came back a tool error naming create-session, and the session table still held one session.

Not reached, by design: a task answer after the client's own 120 s backgrounding — the grace keeps every task answer far inside it. Found in passing: data.json writes a keyword key by its name, so _meta's namespaced keys lost their prefix until the encoder got a key function.