ACP: let clients select the session agent #4475

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1. aheritier

   added

   area/acp

   area/sessionsFor features/issues/fixes related to session lifecycle (resume, persistence, export)For features/issues/fixes related to session lifecycle (resume, persistence, export)

   on Sep 25, 2026
2. aheritier

   added the

   Enhancement

   issue type on Sep 25, 2026
3. gargsajal9 commented on Oct 8, 2026

   

   gargsajal9

   on Oct 8, 2026

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   I traced the ACP lifecycle and confirmed the current behavior with a focused SQLite/fake-provider test: after switching from root to worker, both cold session/load and cold session/resume reconstruct root. Active resume retains the process-local selection.

   Before implementing, can maintainers confirm this first-slice contract?

   • agent represents the ACP session current conversational/entry agent.
   • Advertise team agents in team order, using stable names as values and configured descriptions in the choices.
   • Persist the selection as ACP-owned session metadata (for example, a namespaced acp.agent attribute), rather than reusing transient Session.AgentName or routing/handoff fields.
   • Restore it before returning cold load/resume configuration or accepting a prompt.
   • Treat a removed or renamed persisted agent as an explicit cold-load error, consistent with stale persisted model overrides, rather than silently falling back.
   • Route config-option and agent-switch command changes through the same persistence helper, with active-work rejection and runtime rollback if persistence fails.
   • Hide the agent selector while work is active, matching the existing volatile model/thought selectors.

   I would keep serve acp --agent, other protocol/UI surfaces, team-default changes, and handoff/background/hook-routing semantics out of the first PR. If the metadata representation or stale-agent policy should differ, I can adapt the implementation plan before changing production code.