diff --git a/src/main/java/it/cnr/isti/workflow/manager/blocks/configurations/MCPAgentUploadInput.java b/src/main/java/it/cnr/isti/workflow/manager/blocks/configurations/MCPAgentUploadInput.java
index 4fa9852..da27aa0 100644
--- a/src/main/java/it/cnr/isti/workflow/manager/blocks/configurations/MCPAgentUploadInput.java
+++ b/src/main/java/it/cnr/isti/workflow/manager/blocks/configurations/MCPAgentUploadInput.java
@@ -1,5 +1,6 @@
 package it.cnr.isti.workflow.manager.blocks.configurations;
 
+import com.fasterxml.jackson.annotation.JsonIgnore;
 import com.fasterxml.jackson.annotation.JsonProperty;
 
 import it.cnr.isti.workflow.manager.configurations.annotations.FieldRetriever;
@@ -40,7 +41,15 @@ public record MCPAgentUploadInput(
         this(name, kind, multiple, null);
     }
 
-    /** Whether this attachment comes from a global input rather than a port of its own. */
+    /**
+     * Whether this attachment comes from a global input rather than a port of its own.
+     *
+     * <p>{@code @JsonIgnore} because Jackson reads an is-prefixed no-arg boolean as a property:
+     * without it a "fromGlobalInput" field appeared in every API payload and every persisted flow,
+     * in a shape the schema does not declare - the same trap {@code ModelParameters.isEmpty} carries
+     * the same guard for.
+     */
+    @JsonIgnore
     public boolean isFromGlobalInput() {
         return globalInput != null && !globalInput.isBlank();
     }
diff --git a/src/test/java/it/cnr/isti/workflow/manager/blocks/configurations/MCPAgentUploadGlobalSchemaTest.java b/src/test/java/it/cnr/isti/workflow/manager/blocks/configurations/MCPAgentUploadGlobalSchemaTest.java
new file mode 100644
index 0000000..88e44ba
--- /dev/null
+++ b/src/test/java/it/cnr/isti/workflow/manager/blocks/configurations/MCPAgentUploadGlobalSchemaTest.java
@@ -0,0 +1,55 @@
+package it.cnr.isti.workflow.manager.blocks.configurations;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.TestPropertySource;
+
+import tools.jackson.databind.JsonNode;
+
+import it.cnr.isti.workflow.manager.app.ObjectMapperHolder;
+import it.cnr.isti.workflow.manager.blocks.Block;
+import it.cnr.isti.workflow.manager.blocks.types.MCPAgentBlockType;
+import it.cnr.isti.workflow.manager.controllers.BlocksController;
+
+@SpringBootTest
+@TestPropertySource(locations = "classpath:test.properties")
+public class MCPAgentUploadGlobalSchemaTest {
+
+    @Autowired
+    private JsonSchemaProducer schemaProducer;
+
+    @Autowired
+    private BlocksController blocksController;
+
+    @Test
+    public void theEditorIsToldAnUploadCanNameAGlobal() {
+        JsonNode schema = schemaProducer.generateSchemaNode(MCPAgentBlockConfiguration.class);
+        assertNotNull(schema);
+        String asText = schema.toString();
+        assertTrue(asText.contains("globalInput"), "the upload input schema must carry the new field: " + asText);
+    }
+
+    @Test
+    public void aBlockWhoseUploadNamesAGlobalSurvivesTheRoundTripTheEditorMakes() {
+        // Exactly what the editor posts back when the field is filled from the dropdown.
+        String payload = """
+                {"type":"MCPAgentBlockConfiguration","name":"Read the plan","model":"llama3.1:8b",
+                 "prompt":"Summarize the attached plan","mcpServers":[],
+                 "uploadInputs":[{"name":"planDoc","kind":"DOCUMENT","multiple":false,"globalInput":"document"}],
+                 "shareSession":false,"useSharedSession":false}
+                """;
+        MCPAgentBlockConfiguration configuration =
+                ObjectMapperHolder.mapper.readValue(payload, MCPAgentBlockConfiguration.class);
+        assertEquals("document", configuration.getUploadInputs().getFirst().globalInput());
+
+        Block<MCPAgentBlockType> block = blocksController.create(configuration, null, null);
+
+        assertNotNull(block);
+        assertTrue(block.getInputs().stream().noneMatch(input -> input.getName().equals("planDoc")));
+    }
+}
diff --git a/src/test/java/it/cnr/isti/workflow/manager/blocks/configurations/MCPAgentUploadInputJsonTest.java b/src/test/java/it/cnr/isti/workflow/manager/blocks/configurations/MCPAgentUploadInputJsonTest.java
new file mode 100644
index 0000000..4f08df8
--- /dev/null
+++ b/src/test/java/it/cnr/isti/workflow/manager/blocks/configurations/MCPAgentUploadInputJsonTest.java
@@ -0,0 +1,46 @@
+package it.cnr.isti.workflow.manager.blocks.configurations;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+import tools.jackson.databind.ObjectMapper;
+
+public class MCPAgentUploadInputJsonTest {
+
+    private final ObjectMapper mapper = new ObjectMapper();
+
+    @Test
+    public void readsAnUploadInputThatNamesAGlobal() {
+        MCPAgentUploadInput upload = mapper.readValue(
+                "{\"name\":\"planDoc\",\"kind\":\"DOCUMENT\",\"multiple\":false,\"globalInput\":\"document\"}",
+                MCPAgentUploadInput.class);
+
+        assertEquals("planDoc", upload.name());
+        assertEquals("document", upload.globalInput());
+    }
+
+    @Test
+    public void readsAnUploadInputSavedBeforeGlobalsWereAnOption() {
+        MCPAgentUploadInput upload = mapper.readValue(
+                "{\"name\":\"planDoc\",\"kind\":\"DOCUMENT\",\"multiple\":false}",
+                MCPAgentUploadInput.class);
+
+        assertEquals("planDoc", upload.name());
+        assertNull(upload.globalInput());
+    }
+
+    @Test
+    public void doesNotInventAFieldTheSchemaNeverDeclared() {
+        // Jackson reads an is-prefixed no-arg boolean as a property, so isFromGlobalInput() would
+        // otherwise put a "fromGlobalInput" into every payload and every persisted flow.
+        String written = mapper.writeValueAsString(
+                new MCPAgentUploadInput("planDoc", MCPAgentUploadInput.MCPAgentUploadKind.DOCUMENT, false, "document"));
+
+        assertFalse(written.contains("fromGlobalInput"), written);
+        assertTrue(written.contains("globalInput"), written);
+    }
+}