With multi-agent the only live factory (B1), the single-agent stack is dead.
Remove app/agents/new_chat/ entirely: chat_deepagent.py, subagents/, and all
re-export shims (errors/context/llm_config/permissions/tools/middleware/...) that
existed only to serve frozen single-agent code. Live code already imports the
shared kernel (app.agents.shared.*) directly.
Tests: delete single-agent-only suites (test_resolve_prompt_model_name,
test_specialized_subagents) and the chat_deepagent source-shape contract assertion;
repoint test_scoped_model_fallback to the shared middleware path. Suite green
(2710 passed).
14bbea0854