Make task agents' lead messaging capability clear

internal/agents/manager.go

@@ -899,13 +899,13 @@ func (m *Manager) startLive(ctx context.Context, sess api.AgentSession, task api
 	tools := append([]mcp.Tool{m.askTool(l), m.cancelQuestionTool(l), m.setTitlesTool(l), m.stopMergeTool(l), m.mergeToMainTool(l), m.setTaskSummaryTool(l), m.searchClosedTool(l), m.exposePortTool(l), m.takeSnapshotTool(l), m.terminalReadTool(l), m.terminalTypeTool(l), m.bashTool(l), m.readKnowledgeTool(), m.renderDiagramTool(), m.exportDiagramTool(l), m.randomChoiceTool()}, append(append(m.fileTools(l), m.subtaskTools(l)...), m.clientTools(l)...)...)
 	lead := true
 	if sess.Role == api.Implementer {
-		g += longTitleGuidance(task)
+		g += longTitleGuidance(task) + messageLeadGuidance
 		notes, err := m.notesText(ctx, task.CreatedBy, task.ProjectId)
 		if err != nil {
 			return nil, err
 		}
 		l.notes = "\n\n" + taskNotesGuidance + "\n\n" + notes
-		tools = append(tools, m.suggestNoteTool(l), m.readyForMergeTool(l), m.suggestDiscardTool(l), m.cancelReadyTool(l), m.respondToFindingTool(l))
+		tools = append(tools, m.messageLeadTool(l), m.suggestNoteTool(l), m.readyForMergeTool(l), m.suggestDiscardTool(l), m.cancelReadyTool(l), m.respondToFindingTool(l))
 		if sess.Vendor == api.Claude {
 			tools = append(tools, m.forkTool(l))
 		}

internal/agents/messagelead.go

@@ -0,0 +1,46 @@
+package agents
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"strings"
+
+	"g.fc.run/ai/byre/internal/mcp"
+	"g.fc.run/ai/byre/internal/store"
+)
+
+const messageLeadGuidance = "\n- To contact the human's lead agent, use message_lead with a self-contained message (for example, a task brief the human asked you to pass along). You don't need to find a session or ask the human to paste it. Your final messages also reach the lead automatically."
+
+func (m *Manager) messageLeadTool(l *live) mcp.Tool {
+	return mcp.Tool{
+		Name:        "message_lead",
+		Description: "Send a message to this task creator's lead agent. Use it to pass along a task brief, request coordination, or share information the lead needs before your turn ends. Include all the context the lead needs; it cannot see your conversation. Your final messages already reach the lead automatically.",
+		InputSchema: json.RawMessage(`{"type":"object","properties":{"text":{"type":"string","description":"A self-contained message for the lead."}},"required":["text"]}`),
+		Handler: mcp.Typed(func(ctx context.Context, args struct {
+			Text string `json:"text"`
+		}) (string, error) {
+			text := strings.TrimSpace(args.Text)
+			if text == "" {
+				return "", fmt.Errorf("%w: text must not be empty", ErrInvalid)
+			}
+			task, err := m.store.GetTask(ctx, l.taskID)
+			if err != nil {
+				return "", err
+			}
+			_, found, err := m.activeLead(ctx, task.CreatedBy)
+			if err != nil {
+				return "", err
+			}
+			if !found {
+				return "", fmt.Errorf("%w: %s has no lead agent to receive the message", ErrConflict, task.CreatedBy)
+			}
+			signal := fmt.Sprintf("Message from the agent working on %s (project %s):\n\n%s", m.taskLabel(ctx, task.Id), task.ProjectId, text)
+			err = m.addLeadInput(ctx, store.LeadInput{Owner: task.CreatedBy, Kind: store.LeadSignal, Actor: "byre", Text: signal})
+			if err != nil {
+				return "", err
+			}
+			return "Message sent to the lead.", nil
+		}),
+	}
+}