feat: add HTTP/WebSocket transport for remote ACP agents

[3coins]

Summary

Adds an HTTP/WebSocket transport layer (acp.http) that enables ACP agents and clients to communicate over WebSocket instead of stdio, unlocking remote agent deployments (e.g., cloud-hosted agents accessed by any ACP client over standard WebSocket connections).

Related issues

N/A — new feature. Validated via acp-agentcore-poc, a proof-of-concept integrating DeepAgents with AWS Bedrock AgentCore using this transport. Also validated via jai-remote-acp-persona, that integrates this with Jupyter as the client.

Testing

• uv run python -m pytest tests/test_http_transport.py -v — 13 tests, all passing:
  • WebSocketStreamAdapter lifecycle (start, close, double-start, idempotent close)
  • Bidirectional message flow (receive → reader, writer → send, bytes and text)
  • EOF handling on WebSocket disconnect
  • StarletteWebSocketWrapper delegation (recv, send text/bytes, close)
  • End-to-end agent ↔ client round-trip over WebSocket adapters (initialize, new_session, prompt)
• Existing test suite unaffected (uv run python -m pytest passes)

Docs & screenshots

Demo of AgentCore agent with a test client

agentcore-acp-demo.mp4

Demo of AgentCore agent with Jupyter client

jai-remote-acp-demo.mp4

Documentation updates included in this PR:

• README.md — Updated "At a glance" and "Project layout" to mention HTTP/WebSocket transport
• docs/quickstart.md — New "HTTP/WebSocket (remote agents)" section with server setup, client connection, and programmatic usage examples
• docs/http-transport.md — Dedicated doc page covering architecture (4-queue design), component APIs (WebSocketStreamAdapter, connect_http_agent, WebSocketLike, StarletteWebSocketWrapper), server/client examples, dependencies, and limitations
• mkdocs.yml — Added nav entry for the new doc page
• Two runnable examples: examples/http_echo_agent.py (server) and examples/http_client.py (client)

Checklist

• Conventional Commit title (e.g. feat:, fix:).
• Tests cover the change or are not required (explain above).
• Docs/examples updated when behaviour is user-facing.
• Schema regenerations (make gen-all) are called out if applicable. — N/A, no schema changes.