feat(client): AgentClient.from_mcp_client() factory for in-process MCP transport

[bokelley]

Context

JS client v5.19.0 added AgentClient.fromMCPClient() — a static factory that takes a pre-connected @modelcontextprotocol/sdk Client instance instead of a URL-based agent config. This lets compliance test fleets wire a full AgentClient against an InMemoryTransport pair without standing up a loopback HTTP server.

Python client has no equivalent today: ADCPClient / MCPAdapter always construct their own MCP client from a URL/headers config. Compliance tests that want to exercise the full client path against an in-process server have to either:

• Spin up an HTTP loopback (slow + flaky)
• Mock the adapter (defeats the purpose of integration coverage)

Proposal

Add ADCPClient.from_mcp_client(client, *, agent_id=None) (or equivalent on MCPAdapter) that wraps a pre-connected mcp.client.session.ClientSession. Keep semantics identical to the JS factory:

• MCP only. No A2A equivalent yet (matches JS — JS notes that for A2A, run on a loopback). Don't try to model in-process A2A in this issue.
• Caller owns the lifecycle of the wrapped client (no double-close).
• All existing client surface (skills, signing, validation hooks) works unchanged through the factory path.

Out of scope

• In-process A2A bridge (separate problem, separate issue if/when it matters)
• Refactoring MCPAdapter internals beyond what's needed to accept an injected session

References

• JS factory: @adcp/client v5.19.0 release notes
• Python adapter today: `src/adcp/protocols/mcp.py`
• Use case: compliance test fleets, parity with JS sandbox tooling

[bokelley]

Triage

Classification: Feature request
Bucket(s): client (no client label exists in this repo — gap noted)
Status: drafting-pr
Milestone: omitted (no target version named)

What the experts said:

• code-reviewer: approved — non-breaking additive classmethod; MCPAdapter._get_session() short-circuit makes the injection safe; three issues fixed (None guard on agent_id, explicit RuntimeError replacing assert, ClientSession typing via TYPE_CHECKING)
• dx-expert: approved — session lifecycle contract clearly stated in docstring; mcp.shared.memory.create_client_server_memory_streams example is correct; param ordering aligned with __init__; one known nit (server-wiring comment is a placeholder)

My take: This is a clean, non-breaking addition that closes the JS/Python parity gap for compliance test fleets. Draft PR opened immediately — all PR criteria met (experts converge, non-breaking, tests pass, no pinned dep bumps, no generated-code edits).

Drafting PR: #293 — ADCPClient.from_mcp_client() factory for in-process MCP transport

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Triaged by Claude Code. Session: https://claude.ai/code/session_014Lazxs8FCWcVzzKi8MpLPi

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Generated by Claude Code