feat: add optional Spring REST adapter and catalog SPI

Expose OrdoEngine over conditionally registered HTTP endpoints in autoconfigure, keep JDBC wiring in spring.jdbc, and share definition JSON via ProcessDefinitionParser.toJson.

Co-authored-by: Cursor <cursoragent@cursor.com>

ordo-api/src/main/java/com/jetlumen/ordo/api/OrdoCatalog.java

@@ -0,0 +1,34 @@
+package com.jetlumen.ordo.api;
+
+import java.util.List;
+
+/** Host-registered keys for designers and REST dropdowns; not used by the engine at runtime. */
+public interface OrdoCatalog {
+    List<Item> conditions();
+
+    List<Item> actions();
+
+    List<Item> assignees();
+
+    record Item(String key, String label) {
+    }
+
+    static OrdoCatalog empty() {
+        return new OrdoCatalog() {
+            @Override
+            public List<Item> conditions() {
+                return List.of();
+            }
+
+            @Override
+            public List<Item> actions() {
+                return List.of();
+            }
+
+            @Override
+            public List<Item> assignees() {
+                return List.of();
+            }
+        };
+    }
+}

ordo-api/src/main/java/com/jetlumen/ordo/api/ProcessDefinitionParser.java

@@ -1,5 +1,6 @@
 package com.jetlumen.ordo.api;
 
+import com.fasterxml.jackson.annotation.JsonInclude;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
@@ -10,11 +11,13 @@ import java.time.DateTimeException;
 import java.time.Duration;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;
 import java.util.Objects;
 
 /** Parses a structural JSON process graph into a {@link ProcessDefinition}. */
 public final class ProcessDefinitionParser {
-    private static final ObjectMapper MAPPER = new ObjectMapper();
+    private static final ObjectMapper MAPPER = new ObjectMapper()
+            .setSerializationInclusion(JsonInclude.Include.NON_NULL);
 
     private ProcessDefinitionParser() {
     }
@@ -28,6 +31,15 @@ public final class ProcessDefinitionParser {
         }
     }
 
+    public static String toJson(ProcessDefinition definition) {
+        Objects.requireNonNull(definition, "definition must not be null");
+        try {
+            return MAPPER.writeValueAsString(fromDefinition(definition));
+        } catch (JsonProcessingException e) {
+            throw new IllegalArgumentException("invalid process definition json", e);
+        }
+    }
+
     public static ProcessDefinition fromJson(InputStream json) {
         Objects.requireNonNull(json, "json must not be null");
         try {
@@ -66,6 +78,27 @@ public final class ProcessDefinitionParser {
         return new ProcessDefinition(document.id(), document.name(), steps, transitions);
     }
 
+    private static DefinitionDocument fromDefinition(ProcessDefinition definition) {
+        List<StepDocument> steps = new ArrayList<>(definition.steps().size());
+        for (ApprovalStep step : definition.steps()) {
+            DueDocument due = null;
+            if (step.due() != null) {
+                StepDue stepDue = step.due();
+                due = new DueDocument(stepDue.after().toString(), stepDue.then().name().toLowerCase(Locale.ROOT),
+                        stepDue.to(), stepDue.action());
+            }
+            steps.add(new StepDocument(step.id(), step.name(), step.candidates(), step.policy(), step.kind(),
+                    step.actionKey(), due));
+        }
+        List<TransitionDocument> transitions = new ArrayList<>(definition.transitions().size());
+        for (StepTransition transition : definition.transitions()) {
+            transitions.add(new TransitionDocument(transition.fromStepId(), transition.toStepId(),
+                    transition.conditionKey(), transition.priority()));
+        }
+        return new DefinitionDocument(definition.id(), definition.name(), definition.version(),
+                definition.steps().get(0).id(), steps, transitions);
+    }
+
     private static void rotateStartStep(List<ApprovalStep> steps, String startStepId) {
         if (startStepId == null || startStepId.isBlank()) {
             return;

ordo-api/src/test/java/com/jetlumen/ordo/api/ProcessDefinitionParserTest.java

@@ -7,6 +7,7 @@ import java.util.List;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 class ProcessDefinitionParserTest {
 
@@ -37,8 +38,12 @@ class ProcessDefinitionParserTest {
                 StepTransition.end("hr")
         ));
 
-        assertEquals(expected, ProcessDefinitionParser.fromJson(LEAVE_REQUEST_JSON));
-        assertEquals(0, ProcessDefinitionParser.fromJson(LEAVE_REQUEST_JSON).version());
+        ProcessDefinition definition = ProcessDefinitionParser.fromJson(LEAVE_REQUEST_JSON);
+        assertEquals(expected, definition);
+        assertEquals(0, definition.version());
+        ProcessDefinition roundTrip = ProcessDefinitionParser.fromJson(ProcessDefinitionParser.toJson(definition));
+        assertTrue(definition.sameGraph(roundTrip));
+        assertEquals("manager", roundTrip.steps().get(0).id());
     }
 
     @Test