Keep the handoff continuation message when its turn is folded away

internal/agents/compact.go

@@ -3,6 +3,7 @@ package agents
 import (
 	"context"
 	"log/slog"
+	"strings"
 
 	"g.fc.run/misc/byre/internal/api"
 )
@@ -36,6 +37,10 @@ func isHandoffPrompt(actor, text string) bool {
 	return actor == "byre" && (text == handoffPrompt || text == leadHandoffPrompt)
 }
 
+func isContinuation(actor, text string) bool {
+	return actor == "byre" && (strings.HasPrefix(text, handoffPreamble) || strings.HasPrefix(text, leadHandoffPreamble))
+}
+
 func (m *Manager) continueFromHandoff(sessionID, handoff string) {
 	ctx := context.Background()
 	err := m.handoff(ctx, sessionID, handoff)

internal/agents/manager.go

@@ -592,6 +592,9 @@ func (m *Manager) message(ctx context.Context, l *live, actor, text string, imag
 	if compacting {
 		payload["handoff"] = true
 	}
+	if isContinuation(actor, text) {
+		payload["continuation"] = true
+	}
 	err := m.emit(ctx, l, actor, "user.message", payload)
 	if err != nil {
 		return err

internal/agents/manager_test.go

@@ -595,7 +595,11 @@ func TestCompactCarriesHandoff(t *testing.T) {
 			ev.AgentSessionId != nil && *ev.AgentSessionId != old.Id
 	})
 
+	continued := false
 	for _, ev := range events {
+		if ev.Kind == "user.message" && *ev.AgentSessionId != old.Id {
+			continued = ev.Payload["continuation"] == true
+		}
 		if ev.Kind == "turn.ended" && *ev.AgentSessionId == old.Id {
 			if ev.Payload["handoff"] != true || ev.Payload["inbox_item_id"] != nil {
 				t.Fatalf("handoff turn.ended %v: want handoff and no inbox summary", ev.Payload)
@@ -605,6 +609,9 @@ func TestCompactCarriesHandoff(t *testing.T) {
 			t.Fatalf("handoff prompt %v: want handoff flag", ev.Payload)
 		}
 	}
+	if !continued {
+		t.Fatalf("new session's first message lacks the continuation flag")
+	}
 
 	sessions, err := e.store.ListSessions(e.ctx, e.task.Id)
 	if err != nil {