What

Continues slimming the repo-root miles_agent_server.py toward a thin FastAPI entrypoint. Now that the mutable state (inflight_tasks, trial_projects) lives on the ServerState singleton, the two /flush_all teardown helpers no longer reach into miles globals and can move cleanly.

New agent_server/teardown.py holds:

• _cancel_all_inflight — cancels every in-flight /run task (reads _state.inflight_tasks)
• _kill_trial_containers — tears down the compose projects this server created (reads _state.trial_projects, calls docker_ops._list_compose_projects / _run_docker)

miles_agent_server.py re-imports both (the /flush_all route still calls them) and drops the now-orphaned _list_compose_projects / _run_docker imports. _prune_docker stays (still used directly by the /flush_all handler).

Tests

• Added from agent_server import teardown to test_miles_agent_server_flush_all.py.
• TestKillTrialContainers patches the helper's internal _list_compose_projects / _run_docker calls → repointed to teardown.* (patch-where-used: the moved function resolves those in its own namespace).
• TestListComposeProjects invokes the helper directly → repointed to docker_ops._list_compose_projects() (no longer re-imported into miles).
• /flush_all endpoint tests patch module._cancel_all_inflight / module._kill_trial_containers — unchanged (the route resolves them via the re-import).

Full tests/unit suite: 2854 passed, 1 skipped. ruff check + ruff format --check clean on the changed files.

Stacked

Targets shi/refactor-agent-server-13-trial-runner (#1914). Part of the miles_agent_server.py → agent_server/ decomposition chain.