Two interacting bugs caused asyncio.sleep to be mocked globally,
letting tarpit_watcher_worker spin the event loop on a non-async
mock and accumulate _increment_mock_call records without bound:
1. test_ingester.py patched `decnet.web.ingester.asyncio.sleep` via
the asyncio singleton — any code in the process using asyncio.sleep
(including the tarpit worker) hit the fake_sleep side_effect.
Fix: add `_sleep = asyncio.sleep` alias in ingester.py and patch
`decnet.web.ingester._sleep` instead — scopes the mock to ingester.
2. test_api_startup_guards.py called `_run_lifespan_startup` without
DECNET_CONTRACT_TEST=true, which started the real tarpit task in a
manually-constructed event loop that the tests never cancelled.
Fix: set DECNET_CONTRACT_TEST=true inside _run_lifespan_startup so
the lifespan skips all background workers.
Refuse to start decnet.web.api when DECNET_MODE=agent (unless the
operator explicitly opts into dual-role with DECNET_DISALLOW_MASTER=
false). The Typer CLI already hides master-only commands on agents,
but a misconfigured systemd unit or a direct uvicorn invocation
would bypass that — now the lifespan itself refuses, before any
worker, DB or bus comes up.
Resolve DECNET_JWT_SECRET eagerly at startup so a missing or known-
bad value fails at boot rather than on the first auth-gated request.
The lazy-load shape stays useful for non-master CLIs.
