testing: forward lifespan and MCP session settings from build_asgi_app

[bokelley]

Problem

Beta.5's adcp.testing.build_asgi_app(transport="both") solves the combined
MCP+A2A topology gap from #1047, but it still cannot replace production app
composition for adopters that configure lifespan hooks or stateful MCP
sessions.

The public helper does not accept or forward these production serve() /
_build_mcp_and_a2a_app() inputs:

on_startup
on_shutdown
stateless_http
session_idle_timeout
max_active_sessions

Passing any of them through **factory_kwargs does not work: those kwargs are
forwarded to create_adcp_server_from_platform(), where they are unexpected.

Our in-process app must run cleanup hooks for database-backed proposal/task
stores and must exercise the same MCP session configuration as production.
Consequently, even on beta.5 it still has to import:

from adcp.server.serve import _apply_asgi_middleware, _build_mcp_and_a2a_app

This leaves the private-API dependency #1047 was intended to remove.

Requested API

Add explicit, typed kwargs to build_asgi_app() (and where appropriate
build_test_client()):

build_asgi_app(
    platform,
    transport="both",
    on_startup=(open_resources,),
    on_shutdown=(close_resources,),
    stateless_http=False,
    session_idle_timeout=1800.0,
    max_active_sessions=1000,
)

For transport="both", forward them to the existing production composition
path. Tests should verify that startup/shutdown hooks run under an ASGI lifespan
manager and that the MCP server receives the three session settings.

This is an additive production-parity follow-up to #1047; the beta.5 transport
selection and auth/discovery behavior are otherwise working well.

[bokelley]

Triage

Classification: Feature request
Bucket(s): enhancement
Status: ready-to-implement

What the experts said:

• code-reviewer: Non-breaking additive; must forward all 5 kwargs at the _build_mcp_and_a2a_app() call site or hooks silently never fire; ValueError guard required for hooks on non-"both" transport; three test categories mandatory (ValueError guard, session-kwarg forwarding to create_mcp_server, lifespan hook fires under LifespanManager)
• dx-expert: Design is correct and consistent with production serve(); build_test_client() must also expose all 5 params (that's where LifespanManager fires hooks); max_active_sessions default must be None, not a concrete cap; docstrings need :param entries covering the transport="both" restriction on hook params

My take: Clean production-parity gap — #1047 (merged via #1048) shipped transport="both" but the public testing API doesn't yet forward the lifespan and session-config surface that production serve() exposes. All five new params are optional with production-matching defaults.

• build_asgi_app() signature (src/adcp/testing/decisioning.py): Add on_startup, on_shutdown, stateless_http=False, session_idle_timeout=1800.0, max_active_sessions=None. Add ValueError for hooks on transport != "both" (mirror serve.py:1015); warnings.warn for non-default MCP-only session params when transport="a2a". Forward all 5 to _build_mcp_and_a2a_app() for transport="both"; forward session trio to create_mcp_server() for transport="mcp".
• build_test_client(): Add same 5 kwargs, forward to build_asgi_app().
• Tests: (a) ValueError for hooks with transport="mcp" and transport="a2a"; (b) mock asserts session kwargs reach create_mcp_server; (c) lifespan integration test confirms hook fires through build_test_client(transport="both", on_startup=(...)).
• Non-breaking: all new params optional with defaults matching production; existing callers unaffected.

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Triaged by Claude Code. Session: https://claude.ai/code/cse_01E5ECmJ7hNYWY5DoeKvcJU8

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Generated by Claude Code