Migrate Deep Agents to Pydantic AI Harness

Preserve the application's observed contracts, not the shape of create_deep_agent. Compose Pydantic AI primitives and Harness capabilities; keep infrastructure with the application that already owns it.

Establish the source contract

1. Resolve the deepagents import origin before applying these mappings. Route a local module or project-owned create_deep_agent to the ordinary LangChain migration only when its implementation has ordinary LangChain or LangGraph semantics; vendored implementations that reproduce Deep Agents contracts remain in scope. Read repository instructions, manifests, lockfiles, tests, runtime entrypoints, and the resolved source. Record exact Deep Agents, LangChain, LangGraph, Pydantic AI, and Harness versions. If the locked source is unavailable, reproduce its environment without changing the target lockfile. If that is not possible, mark affected behavior unverified and do not claim parity.
2. Trace one representative request through prompt and model profile, tools and integrations, middleware and permissions, backend and execution, skills and memory, delegation, state, checkpoints and approvals, retries and limits, events, side effects, and the public boundary. Inspect every caller of that boundary.
3. Run the cheapest deterministic baseline. Record evidence separately from the outcome: source-inspected, probe-observed, or regression-tested.
4. Load only the mapping needed for the detected source features:
   • Core Migration for construction, models and profiles, prompts, tools and MCP, middleware, state, outputs, caching, or tracing.
   • Context and Execution for coding-agent defaults, planning, files, permissions, backends, sandboxes, interpreters, media, skills, memory, retrieval, or context limits.
   • Orchestration and Recovery for synchronous, dynamic, or background subagents; grading loops; approvals; checkpoints; fault tolerance; durable execution; or streaming.
   • Hosts and Protocols only when migrating Deep Agents Code, a frontend, ACP, A2A, or a deployment boundary.

Build the Pydantic AI target