refactor(mcp): Modularize direct functions in MCP server

Split monolithic task-master-core.js into separate function files within
the mcp-server/src/core/direct-functions/ directory. This change:

- Creates individual files for each direct function implementation
- Moves findTasksJsonPath to a dedicated utils/path-utils.js file
- Converts task-master-core.js to be a simple import/export hub
- Improves maintainability and organization of the codebase
- Reduces potential merge conflicts when multiple developers contribute
- Follows standard module separation patterns

Each function is now in its own self-contained file with clear imports and
focused responsibility, while maintaining the same API endpoints.

mcp-server/src/core/direct-functions/update-tasks.js

@@ -0,0 +1,99 @@
+/**
+ * update-tasks.js
+ * Direct function implementation for updating tasks based on new context/prompt
+ */
+
+import { updateTasks } from '../../../../scripts/modules/task-manager.js';
+import { findTasksJsonPath } from '../utils/path-utils.js';
+
+/**
+ * Direct function wrapper for updating tasks based on new context/prompt.
+ * 
+ * @param {Object} args - Command arguments containing fromId, prompt, useResearch and file path options.
+ * @param {Object} log - Logger object.
+ * @returns {Promise<Object>} - Result object with success status and data/error information.
+ */
+export async function updateTasksDirect(args, log) {
+  try {
+    log.info(`Updating tasks with args: ${JSON.stringify(args)}`);
+    
+    // Check required parameters
+    if (!args.from) {
+      const errorMessage = 'No from ID specified. Please provide a task ID to start updating from.';
+      log.error(errorMessage);
+      return { 
+        success: false, 
+        error: { code: 'MISSING_FROM_ID', message: errorMessage },
+        fromCache: false 
+      };
+    }
+    
+    if (!args.prompt) {
+      const errorMessage = 'No prompt specified. Please provide a prompt with new context for task updates.';
+      log.error(errorMessage);
+      return { 
+        success: false, 
+        error: { code: 'MISSING_PROMPT', message: errorMessage },
+        fromCache: false 
+      };
+    }
+    
+    // Parse fromId - handle both string and number values
+    let fromId;
+    if (typeof args.from === 'string') {
+      fromId = parseInt(args.from, 10);
+      if (isNaN(fromId)) {
+        const errorMessage = `Invalid from ID: ${args.from}. Task ID must be a positive integer.`;
+        log.error(errorMessage);
+        return { 
+          success: false, 
+          error: { code: 'INVALID_FROM_ID', message: errorMessage },
+          fromCache: false 
+        };
+      }
+    } else {
+      fromId = args.from;
+    }
+    
+    // Get tasks file path
+    let tasksPath;
+    try {
+      tasksPath = findTasksJsonPath(args, log);
+    } catch (error) {
+      log.error(`Error finding tasks file: ${error.message}`);
+      return { 
+        success: false, 
+        error: { code: 'TASKS_FILE_ERROR', message: error.message },
+        fromCache: false 
+      };
+    }
+    
+    // Get research flag
+    const useResearch = args.research === true;
+    
+    log.info(`Updating tasks from ID ${fromId} with prompt "${args.prompt}" and research: ${useResearch}`);
+    
+    // Execute core updateTasks function
+    await updateTasks(tasksPath, fromId, args.prompt, useResearch);
+    
+    // Since updateTasks doesn't return a value but modifies the tasks file,
+    // we'll return a success message
+    return {
+      success: true,
+      data: {
+        message: `Successfully updated tasks from ID ${fromId} based on the prompt`,
+        fromId,
+        tasksPath,
+        useResearch
+      },
+      fromCache: false // This operation always modifies state and should never be cached
+    };
+  } catch (error) {
+    log.error(`Error updating tasks: ${error.message}`);
+    return { 
+      success: false, 
+      error: { code: 'UPDATE_TASKS_ERROR', message: error.message || 'Unknown error updating tasks' },
+      fromCache: false 
+    };
+  }
+}