Business Core
+-- Marketing          <--can talk--> Developer PM
+-- Developer PM       <--can talk--> Operations
|   +-- Frontend       <--can talk--> Backend
|   +-- Backend        <--can talk--> QA PM
|   +-- QA PM
|       +-- Auto Test  <--can talk--> Manual Review
|       +-- Manual Review
+-- Operations

func CanCommunicate(callerID, targetID string) bool {
    caller := db.GetWorkspace(callerID)
    target := db.GetWorkspace(targetID)

    // siblings — same parent (including root-level where both have no parent)
    if caller.ParentID != nil && target.ParentID != nil &&
       *caller.ParentID == *target.ParentID {
        return true
    }
    // root-level siblings — both have no parent
    if caller.ParentID == nil && target.ParentID == nil {
        return true
    }

    // parent talking to child
    if caller.ID == target.ParentID {
        return true
    }

    // child talking up to parent
    if target.ID == caller.ParentID {
        return true
    }

    return false
}

GET /registry/:id/peers

async def get_reachable_workspaces(workspace_id: str) -> list:
    ws = db.GetWorkspace(workspace_id)
    reachable = []

    # siblings — same parent
    if ws.parent_id:
        siblings = db.GetChildren(ws.parent_id)
        reachable += [s for s in siblings if s.id != workspace_id]

    # children — own sub-workspaces
    children = db.GetChildren(workspace_id)
    reachable += children

    # parent — can talk up
    if ws.parent_id:
        parent = db.GetWorkspace(ws.parent_id)
        reachable.append(parent)

    return reachable