fix(bridge): reconstruct relay reply context (#514)

core/bridge.go

@@ -60,6 +60,18 @@ type bridgeReplyCtx struct {
 	ReplyCtx   string `json:"reply_ctx"`
 }
 
+const bridgeReconstructReplyCtxKind = "bridge_reconstruct"
+
+// bridgeReconstructReplyCtxPayload is a forward-compatible reply envelope for
+// reconstruct_reply adapters. Receivers should ignore unknown fields.
+type bridgeReconstructReplyCtxPayload struct {
+	Kind                string `json:"kind"`
+	Version             int    `json:"v"`
+	SenderProject       string `json:"sender_project"`
+	TransportChatID     string `json:"transport_chat_id"`
+	TransportSessionKey string `json:"transport_session_key,omitempty"`
+}
+
 // --- Wire protocol messages ---
 
 type bridgeMsg struct {
@@ -305,13 +317,44 @@ func (bp *BridgePlatform) ReconstructReplyCtx(sessionKey string) (any, error) {
 	if !a.capabilities["reconstruct_reply"] {
 		return nil, fmt.Errorf("bridge: adapter %q does not support reconstruct_reply", platform)
 	}
+	replyCtx, err := buildBridgeReconstructReplyCtx(bp.project, sessionKey)
+	if err != nil {
+		return nil, err
+	}
 	return &bridgeReplyCtx{
 		Platform:   platform,
 		SessionKey: sessionKey,
-		ReplyCtx:   sessionKey,
+		ReplyCtx:   replyCtx,
 	}, nil
 }
 
+func buildBridgeReconstructReplyCtx(project, sessionKey string) (string, error) {
+	chatID, err := bridgeTransportChatID(sessionKey)
+	if err != nil {
+		return "", err
+	}
+	payload := bridgeReconstructReplyCtxPayload{
+		Kind:                bridgeReconstructReplyCtxKind,
+		Version:             1,
+		SenderProject:       project,
+		TransportChatID:     chatID,
+		TransportSessionKey: sessionKey,
+	}
+	data, err := json.Marshal(payload)
+	if err != nil {
+		return "", fmt.Errorf("bridge: marshal reconstruct reply ctx: %w", err)
+	}
+	return string(data), nil
+}
+
+func bridgeTransportChatID(sessionKey string) (string, error) {
+	parts := strings.SplitN(sessionKey, ":", 3)
+	if len(parts) < 2 || parts[1] == "" {
+		return "", fmt.Errorf("bridge: invalid session key %q", sessionKey)
+	}
+	return parts[1], nil
+}
+
 func (bp *BridgePlatform) SendCard(ctx context.Context, replyCtx any, card *Card) error {
 	rc, ok := replyCtx.(*bridgeReplyCtx)
 	if !ok {

core/bridge_test.go

@@ -252,6 +252,63 @@ func TestBridge_ReplyRouting(t *testing.T) {
 	}
 }
 
+func TestBridge_ReconstructReplyCtx_RequiresCapability(t *testing.T) {
+	bs, wsURL := startTestBridge(t, "")
+	bp := bs.NewPlatform("advisor-gemini")
+
+	conn := dialWS(t, wsURL, nil)
+	register(t, conn, "bridge", []string{"text"})
+
+	_, err := bp.ReconstructReplyCtx("bridge:1491487450722341088:relay")
+	if err == nil || !strings.Contains(err.Error(), "does not support reconstruct_reply") {
+		t.Fatalf("ReconstructReplyCtx() error = %v, want reconstruct_reply capability error", err)
+	}
+}
+
+func TestBridge_ReconstructReplyCtx_UsesStructuredPayload(t *testing.T) {
+	bs, wsURL := startTestBridge(t, "")
+	bp := bs.NewPlatform("advisor-gemini")
+
+	conn := dialWS(t, wsURL, nil)
+	register(t, conn, "bridge", []string{"text", "reconstruct_reply"})
+
+	replyCtx, err := bp.ReconstructReplyCtx("bridge:1491487450722341088:relay")
+	if err != nil {
+		t.Fatalf("ReconstructReplyCtx() error = %v", err)
+	}
+
+	rc, ok := replyCtx.(*bridgeReplyCtx)
+	if !ok {
+		t.Fatalf("reply ctx type = %T, want *bridgeReplyCtx", replyCtx)
+	}
+	if rc.Platform != "bridge" {
+		t.Fatalf("Platform = %q, want bridge", rc.Platform)
+	}
+	if rc.SessionKey != "bridge:1491487450722341088:relay" {
+		t.Fatalf("SessionKey = %q, want relay session key", rc.SessionKey)
+	}
+
+	var payload bridgeReconstructReplyCtxPayload
+	if err := json.Unmarshal([]byte(rc.ReplyCtx), &payload); err != nil {
+		t.Fatalf("unmarshal reply_ctx: %v", err)
+	}
+	if payload.Kind != bridgeReconstructReplyCtxKind {
+		t.Fatalf("kind = %q, want %q", payload.Kind, bridgeReconstructReplyCtxKind)
+	}
+	if payload.Version != 1 {
+		t.Fatalf("version = %d, want 1", payload.Version)
+	}
+	if payload.SenderProject != "advisor-gemini" {
+		t.Fatalf("sender_project = %q, want advisor-gemini", payload.SenderProject)
+	}
+	if payload.TransportChatID != "1491487450722341088" {
+		t.Fatalf("transport_chat_id = %q, want 1491487450722341088", payload.TransportChatID)
+	}
+	if payload.TransportSessionKey != "bridge:1491487450722341088:relay" {
+		t.Fatalf("transport_session_key = %q, want relay session key", payload.TransportSessionKey)
+	}
+}
+
 func TestBridge_CardFallback(t *testing.T) {
 	bs, wsURL := startTestBridge(t, "")