Implemented the core infrastructure for the Code Execution Engine

- Implemented the exchange data types for the Code Execution Engine
- Adjusted the ServiceTarget for the Code Execution Engine
- Implemented data types for the Code Execution Engine
- Added a Code Execution Engine service type
- Added a more fields to the ServiceTarget

This solves issue #42

Author: orpiske

capabilities-api/src/main/java/ai/wanaku/capabilities/sdk/api/types/execution/CodeExecutionError.java

@@ -0,0 +1,148 @@
+/*
+ * Copyright 2026 Wanaku AI
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package ai.wanaku.capabilities.sdk.api.types.execution;
+
+import com.fasterxml.jackson.annotation.JsonProperty;
+import java.util.Map;
+
+/**
+ * Error response DTO for code execution failures.
+ * <p>
+ * This class represents error responses returned by the code execution
+ * endpoints when validation fails, tasks are not found, or execution
+ * errors occur.
+ * </p>
+ */
+public class CodeExecutionError {
+
+    /**
+     * The error type or category.
+     * Examples: "VALIDATION_ERROR", "NOT_FOUND", "EXECUTION_ERROR", "TIMEOUT"
+     */
+    @JsonProperty("error")
+    private String error;
+
+    /**
+     * Human-readable error message describing what went wrong.
+     */
+    @JsonProperty("message")
+    private String message;
+
+    /**
+     * The task ID if applicable.
+     * Present when the error relates to a specific task.
+     */
+    @JsonProperty("taskId")
+    private String taskId;
+
+    /**
+     * The timestamp when the error occurred (Unix timestamp in milliseconds).
+     */
+    @JsonProperty("timestamp")
+    private Long timestamp;
+
+    /**
+     * Additional error details as key-value pairs.
+     * Can include field-specific validation errors, stack traces, etc.
+     */
+    @JsonProperty("details")
+    private Map<String, String> details;
+
+    /**
+     * Default constructor for JSON serialization.
+     */
+    public CodeExecutionError() {
+        this.timestamp = System.currentTimeMillis();
+    }
+
+    /**
+     * Constructor with error type and message.
+     *
+     * @param error the error type
+     * @param message the error message
+     */
+    public CodeExecutionError(String error, String message) {
+        this.error = error;
+        this.message = message;
+        this.timestamp = System.currentTimeMillis();
+    }
+
+    /**
+     * Constructor with all fields except details.
+     *
+     * @param error the error type
+     * @param message the error message
+     * @param taskId the task ID
+     */
+    public CodeExecutionError(String error, String message, String taskId) {
+        this.error = error;
+        this.message = message;
+        this.taskId = taskId;
+        this.timestamp = System.currentTimeMillis();
+    }
+
+    // Getters and Setters
+
+    public String getError() {
+        return error;
+    }
+
+    public void setError(String error) {
+        this.error = error;
+    }
+
+    public String getMessage() {
+        return message;
+    }
+
+    public void setMessage(String message) {
+        this.message = message;
+    }
+
+    public String getTaskId() {
+        return taskId;
+    }
+
+    public void setTaskId(String taskId) {
+        this.taskId = taskId;
+    }
+
+    public Long getTimestamp() {
+        return timestamp;
+    }
+
+    public void setTimestamp(Long timestamp) {
+        this.timestamp = timestamp;
+    }
+
+    public Map<String, String> getDetails() {
+        return details;
+    }
+
+    public void setDetails(Map<String, String> details) {
+        this.details = details;
+    }
+
+    @Override
+    public String toString() {
+        return "CodeExecutionError{" + "error='"
+                + error + '\'' + ", message='"
+                + message + '\'' + ", taskId='"
+                + taskId + '\'' + ", timestamp="
+                + timestamp + ", details="
+                + details + '}';
+    }
+}