refactor(acp): route server through assembled runtime

[limityan]

Summary

• assemble the CLI-hosted ACP server with DeliveryProfile::Acp, validated runtime services, harnesses, and the public Agent Runtime SDK
• route ACP session creation/listing, dialog submission, cancellation, interaction responses, and Agentic event delivery through the assembled runtime
• add a session-scoped SDK event subscription owned by the existing Agentic Event Queue so unrelated sessions cannot exhaust an ACP prompt's event budget
• preserve full persisted restore, model/mode, MCP, client lifecycle, stdio, and protocol projection behind the existing Core/ACP compatibility boundaries
• add a production-process stdio initialization smoke test and include CLI, ACP, and Agent Runtime tests in the existing CLI CI job

Product and architecture boundaries

• ACP rejects a second prompt atomically before enqueue while a session is busy; CLI/TUI, Desktop, and remote queue behavior is unchanged
• prompt completion is scoped to the exact turn; a lagged or closed session event subscription cancels that turn and returns an explicit error
• the Agentic Event Queue remains the only event owner: the existing global bounded broadcast continues to serve CLI/TUI, while an active ACP prompt uses a temporary 1,024-event channel containing only its session's events
• the scoped channel is removed when its final receiver is dropped; no per-session forwarding task or second event schema is introduced
• the existing four-argument CoreProductAgentRuntime::build API remains compatible; ACP event injection is additive through build_acp
• image prompt blocks are converted into portable runtime attachments without introducing ACP types into shared runtime contracts
• no ACP wire-schema, UI, keybinding, extension execution, or runtime-owner migration scope is added
• only stable architecture documentation is updated; implementation process specs and plans are excluded

Runtime impact

Concern	Before	After
ACP event isolation	ACP read the global bounded broadcast	An active prompt receives only its session's events through a temporary 1,024-event channel
CLI/TUI event path	Existing global broadcast and one legacy queue drain	Unchanged; with no scoped subscriber, enqueue adds one atomic fast-path check
Host tasks	One legacy queue drain	One legacy queue drain; no per-session forwarding task
Prompt admission	A queued ACP prompt could cross protocol turn boundaries	Busy ACP sessions reject before enqueue under the session lock
Runtime ownership	Core coordinator/scheduler/persistence and Agentic Event Queue	Unchanged; assembly only selects adapters and services

No additional scheduler, persistence manager, runtime owner, background forwarding task, or protocol schema is introduced. Session-scoped channel memory exists only while a consumer is active and is released with the final receiver.

Validation

• cargo +nightly test -p bitfun-agent-runtime -p bitfun-acp -p bitfun-cli (all unit, contract, doc, and integration tests passed)
• production bitfun-cli acp stdio initialize smoke with isolated storage roots
• cargo +nightly test -p bitfun-core (1,101 passed, 1 ignored; the existing timing-sensitive slow_provider_is_not_respawned_while_healthy_sibling_updates failed only under concurrent compile contention and passed 3/3 in isolation)
• cargo +nightly fmt --all -- --check
• node --test scripts/check-core-boundaries.test.mjs
• node scripts/check-core-boundaries.mjs
• git diff --check