feat: add transport ABC + AnthropicTransport wired to all paths
Add ProviderTransport ABC (4 abstract methods: convert_messages,
convert_tools, build_kwargs, normalize_response) plus optional hooks
(validate_response, extract_cache_stats, map_finish_reason).
Add transport registry with lazy discovery — get_transport() auto-imports
transport modules on first call.
Add AnthropicTransport — delegates to existing anthropic_adapter.py
functions, wired to ALL Anthropic code paths in run_agent.py:
- Main normalize loop (L10775)
- Main build_kwargs (L6673)
- Response validation (L9366)
- Finish reason mapping (L9534)
- Cache stats extraction (L9827)
- Truncation normalize (L9565)
- Memory flush build_kwargs + normalize (L7363, L7395)
- Iteration-limit summary + retry (L8465, L8498)
Zero direct adapter imports remain for transport methods. Client lifecycle,
streaming, auth, and credential management stay on AIAgent.
20 new tests (ABC contract, registry, AnthropicTransport methods).
359 anthropic-related tests pass (0 failures).
PR 3 of the provider transport refactor.
731f4fbae6