test(slice-2): integration test + Python echo brain + LEARNING pointers
- Integration test: smoke test against in-process EchoServer (hello
handshake round-trip). Full end-to-end + reconnect-path tests adapt
to slice-1's existing integration-test harness.
- examples/echo_brain/: Python reference brain (~80 lines, websockets lib).
README documents runtime posture + why a Python brain complements the
Rust one (language-agnosticism vs wire-types-reusability).
- LEARNING.md: 5 new pointers (mpsc/oneshot, VecDeque ring, async WS,
Box<dyn Trait> field widening, zero-sized marker newtype).
Spec ref: 2026-06-28-slice-2-agent-tap-design.md §8.4, §8.5 #7.
411276bfde