feat: centralize send message production gate

internal/tools/isphere_send_message_test.go

@@ -147,6 +147,47 @@ func TestISphereSendMessageProductionIsBlockedWithoutSideEffects(t *testing.T) {
 	}
 }
 
+func TestISphereSendMessageProductionBlockedIncludesGateReason(t *testing.T) {
+	audit := &fakeSendMessageAuditSink{}
+	session, cleanup := connectToolsTestSession(t, func(server *mcp.Server) {
+		RegisterISphereSendMessageToolWithState(server, audit, newFakeSendMessageIdempotencyStore())
+	})
+	defer cleanup()
+
+	content := "blocked gate reason"
+	callResult, err := session.CallTool(context.Background(), &mcp.CallToolParams{
+		Name: ToolNameSendMessage,
+		Arguments: map[string]any{
+			"target_type":     "direct",
+			"target_id":       "alice@imopenfire1-lanzhou",
+			"content_text":    content,
+			"content_sha256":  sha256HexForSendMessageTest(content),
+			"idempotency_key": "idem-gate-reason-1",
+			"execution_mode":  "production",
+		},
+	})
+	if err != nil {
+		t.Fatalf("call production blocked gate reason: %v", err)
+	}
+
+	var decoded struct {
+		OK                bool   `json:"ok"`
+		SendStatus        string `json:"send_status"`
+		GateReasonCode    string `json:"gate_reason_code"`
+		GateReasonMessage string `json:"gate_reason_message"`
+	}
+	payload, _ := json.Marshal(callResult.StructuredContent)
+	if err := json.Unmarshal(payload, &decoded); err != nil {
+		t.Fatalf("decode payload %s: %v", payload, err)
+	}
+	if decoded.OK || decoded.SendStatus != "blocked" || decoded.GateReasonCode != "send_disabled_by_default" || decoded.GateReasonMessage == "" {
+		t.Fatalf("production blocked response missing gate reason: %s", payload)
+	}
+	if len(audit.events) != 1 || audit.events[0].GateReasonCode != "send_disabled_by_default" || audit.events[0].GateReasonMessage == "" {
+		t.Fatalf("audit event missing gate reason: %+v", audit.events)
+	}
+}
+
 func TestISphereSendMessageFakeConnectorAcceptedAudit(t *testing.T) {
 	audit := &fakeSendMessageAuditSink{}
 	idempotency := newFakeSendMessageIdempotencyStore()