fix: resolve blackboard split-brain in multi-agent tools

Tools were bound to a static board at registration time while the
system prompt injected data from a separate per-session board.
Add BoardAware interface and SetBoard() methods so tools receive
the correct session blackboard before each execution cycle.

pkg/agent/loop.go

@@ -174,14 +174,14 @@ func registerSharedTools(cfg *config.Config, msgBus *bus.MessageBus, registry *A
 		if len(registry.ListAgentIDs()) > 1 {
 			resolver := &registryResolver{registry: registry}
 
-			// Blackboard tool: per-agent instance sharing a common blackboard
-			// The actual blackboard is created per session in getOrCreateBlackboard
-			// For tool registration, we use a shared "global" blackboard.
-			sharedBoard := multiagent.NewBlackboard()
-			agent.Tools.Register(multiagent.NewBlackboardTool(sharedBoard, agentID))
+			// Blackboard tool: per-agent instance sharing a placeholder blackboard.
+			// The actual per-session blackboard is wired via SetBoard in updateToolContexts
+			// before each message processing cycle (fixing the split-brain bug).
+			placeholderBoard := multiagent.NewBlackboard()
+			agent.Tools.Register(multiagent.NewBlackboardTool(placeholderBoard, agentID))
 
 			// Handoff tool: delegate tasks to other agents
-			agent.Tools.Register(multiagent.NewHandoffTool(resolver, sharedBoard, agentID))
+			agent.Tools.Register(multiagent.NewHandoffTool(resolver, placeholderBoard, agentID))
 
 			// List agents tool: discover available agents
 			agent.Tools.Register(multiagent.NewListAgentsTool(resolver))
@@ -438,8 +438,8 @@ func (al *AgentLoop) runAgentLoop(ctx context.Context, agent *AgentInstance, opt
 		}
 	}
 
-	// 1. Update tool contexts
-	al.updateToolContexts(agent, opts.Channel, opts.ChatID)
+	// 1. Update tool contexts (including per-session blackboard wiring)
+	al.updateToolContexts(agent, opts.Channel, opts.ChatID, opts.SessionKey)
 
 	// 2. Build messages (skip history for heartbeat)
 	var history []providers.Message
@@ -742,8 +742,9 @@ func (al *AgentLoop) runLLMIteration(ctx context.Context, agent *AgentInstance,
 	return finalContent, iteration, nil
 }
 
-// updateToolContexts updates the context for tools that need channel/chatID info.
-func (al *AgentLoop) updateToolContexts(agent *AgentInstance, channel, chatID string) {
+// updateToolContexts updates the context for tools that need channel/chatID info
+// and wires the per-session blackboard to board-aware tools.
+func (al *AgentLoop) updateToolContexts(agent *AgentInstance, channel, chatID string, sessionKey string) {
 	// Use ContextualTool interface instead of type assertions
 	if tool, ok := agent.Tools.Get("message"); ok {
 		if mt, ok := tool.(tools.ContextualTool); ok {
@@ -765,6 +766,20 @@ func (al *AgentLoop) updateToolContexts(agent *AgentInstance, channel, chatID st
 			ht.SetContext(channel, chatID)
 		}
 	}
+
+	// Wire the per-session blackboard to board-aware tools (fixes split-brain bug).
+	// This ensures BlackboardTool and HandoffTool operate on the same board that
+	// gets injected into the system prompt via getOrCreateBlackboard.
+	if sessionKey != "" {
+		bb := al.getOrCreateBlackboard(sessionKey)
+		for _, toolName := range []string{"blackboard", "handoff"} {
+			if tool, ok := agent.Tools.Get(toolName); ok {
+				if ba, ok := tool.(multiagent.BoardAware); ok {
+					ba.SetBoard(bb)
+				}
+			}
+		}
+	}
 }
 
 // getOrCreateBlackboard returns the blackboard for a session, creating one if needed.

pkg/multiagent/blackboard.go

@@ -16,6 +16,13 @@ type BlackboardEntry struct {
 	Timestamp time.Time `json:"timestamp"`
 }
 
+// BoardAware is implemented by tools that need the session blackboard injected
+// before each execution. This fixes the split-brain bug where tools were bound
+// to a static board at registration time instead of the per-session board.
+type BoardAware interface {
+	SetBoard(board *Blackboard)
+}
+
 // Blackboard is a thread-safe shared context pool for multi-agent collaboration.
 // Agents read and write string key-value entries, each tagged with authorship
 // and scope metadata.

pkg/multiagent/blackboard_tool.go

@@ -23,6 +23,12 @@ func NewBlackboardTool(board *Blackboard, agentID string) *BlackboardTool {
 	}
 }
 
+// SetBoard replaces the blackboard reference, allowing the tool to be wired
+// to the correct per-session board before each execution.
+func (t *BlackboardTool) SetBoard(board *Blackboard) {
+	t.board = board
+}
+
 // Name returns the tool name.
 func (t *BlackboardTool) Name() string { return "blackboard" }
 

pkg/multiagent/handoff_tool.go

@@ -85,6 +85,12 @@ func (t *HandoffTool) Parameters() map[string]any {
 	}
 }
 
+// SetBoard replaces the blackboard reference, allowing the tool to be wired
+// to the correct per-session board before each execution.
+func (t *HandoffTool) SetBoard(board *Blackboard) {
+	t.board = board
+}
+
 // SetContext updates the origin channel and chat ID for handoff routing.
 func (t *HandoffTool) SetContext(channel, chatID string) {
 	t.originChannel = channel