feat(llc): Union assignment model — human | agent co-assignees, co-working mode #8230

Parent

Phase 4 (#8208) · Umbrella (#8204)

Depends On

#8223 — Human claim. #8227 — AutoBot agent adapter.

Context

The fundamental model: any work item can be owned by exactly one primary assignee (human OR agent) but can have a secondary co-worker in co-working mode. Subtasks can be split — agent owns some, human owns others — under the same parent.

Acceptance Criteria

• llc_work_items extended with:
  • co_worker_type ENUM(agent, human) nullable
  • co_worker_agent_id UUID FK nullable
  • co_worker_user_id UUID FK nullable
  • co_working_enabled BOOLEAN DEFAULT FALSE
• AssignmentService.enable_coworking(work_item_id, co_worker) — sets co-worker fields. Requires board or lead permission.
• Co-working invariant: in co-working mode, atomic checkout still applies to primary assignee. Co-worker can read and comment freely; co-worker can create subtasks without checkout on parent.
• POST /api/llc/work-items/{id}/coworker — set/clear co-worker
• GET /api/llc/work-items/{id} returns full assignee display: primary + co-worker (if set)
• Work item list supports filter ?co_worker_user_id= and ?co_worker_agent_id=
• All assignment changes written to activity log
• python -m pytest autobot-backend/llc/ -k assignment or cowork passes