Use jsoncreator for AgentMode ctor, per review comments. (#1465)

* Apply review comments

* Address PR review comments on AgentMode

- Revert @SInCE tag from 1.1.0 to 1.0.0 for consistency with
  SendMessageRequest which already references AgentMode
- Fix error message format to 'Unknown AgentMode value: ...' matching
  the convention used by generated enum fromValue methods
- Add AgentModeTest covering serialization, deserialization, round-trip,
  null handling, and unknown-value error behavior

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

---------

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: edburns

java/src/main/java/com/github/copilot/rpc/AgentMode.java

@@ -4,6 +4,7 @@
 
 package com.github.copilot.rpc;
 
+import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonValue;
 
 /**
@@ -44,4 +45,28 @@ public enum AgentMode {
     public String getValue() {
         return value;
     }
+
+    /**
+     * Deserializes a JSON string value into the corresponding {@code AgentMode}
+     * enum constant.
+     *
+     * @param value
+     *            the JSON string value
+     * @return the matching {@code AgentMode}, or {@code null} if value is
+     *         {@code null}
+     * @throws IllegalArgumentException
+     *             if the value does not match any known agent mode
+     */
+    @JsonCreator
+    public static AgentMode fromValue(String value) {
+        if (value == null) {
+            return null;
+        }
+        for (AgentMode mode : values()) {
+            if (mode.value.equals(value)) {
+                return mode;
+            }
+        }
+        throw new IllegalArgumentException("Unknown AgentMode value: " + value);
+    }
 }

java/src/test/java/com/github/copilot/AgentModeTest.java

@@ -0,0 +1,70 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *--------------------------------------------------------------------------------------------*/
+
+package com.github.copilot;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.EnumSource;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.github.copilot.rpc.AgentMode;
+
+/**
+ * Unit tests for {@link AgentMode} serialization, deserialization, and
+ * unknown-value behavior.
+ */
+public class AgentModeTest {
+
+    private final ObjectMapper mapper = new ObjectMapper();
+
+    @ParameterizedTest
+    @EnumSource(AgentMode.class)
+    void jsonRoundTrip_allValues(AgentMode mode) throws Exception {
+        String json = mapper.writeValueAsString(mode);
+        AgentMode deserialized = mapper.readValue(json, AgentMode.class);
+        assertEquals(mode, deserialized);
+    }
+
+    @Test
+    void getValue_returnsExpectedStrings() {
+        assertEquals("interactive", AgentMode.INTERACTIVE.getValue());
+        assertEquals("plan", AgentMode.PLAN.getValue());
+        assertEquals("autopilot", AgentMode.AUTOPILOT.getValue());
+        assertEquals("shell", AgentMode.SHELL.getValue());
+    }
+
+    @Test
+    void fromValue_knownValues_returnsCorrectEnum() {
+        assertEquals(AgentMode.INTERACTIVE, AgentMode.fromValue("interactive"));
+        assertEquals(AgentMode.PLAN, AgentMode.fromValue("plan"));
+        assertEquals(AgentMode.AUTOPILOT, AgentMode.fromValue("autopilot"));
+        assertEquals(AgentMode.SHELL, AgentMode.fromValue("shell"));
+    }
+
+    @Test
+    void fromValue_null_returnsNull() {
+        assertNull(AgentMode.fromValue(null));
+    }
+
+    @Test
+    void fromValue_unknownValue_throwsWithConsistentMessage() {
+        var ex = assertThrows(IllegalArgumentException.class, () -> AgentMode.fromValue("unknown"));
+        assertEquals("Unknown AgentMode value: unknown", ex.getMessage());
+    }
+
+    @Test
+    void jsonDeserialize_unknownValue_throws() {
+        String json = "\"not-a-mode\"";
+        assertThrows(Exception.class, () -> mapper.readValue(json, AgentMode.class));
+    }
+
+    @Test
+    void jsonSerialize_writesStringValue() throws Exception {
+        String json = mapper.writeValueAsString(AgentMode.AUTOPILOT);
+        assertEquals("\"autopilot\"", json);
+    }
+}