feat: add update_task tool and return task ID from schedule_task

schedule_task was creating duplicate tasks when users asked to modify
a schedule, because the agent had no way to update an existing task
and didn't know the ID of the task it created. Now schedule_task
generates and returns the task ID, and a new update_task tool allows
modifying prompt, schedule_type, and schedule_value in place.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/ipc.ts

@@ -247,7 +247,9 @@ export async function processTaskIpc(
           nextRun = scheduled.toISOString();
         }
 
-        const taskId = `task-${Date.now()}-${Math.random().toString(36).slice(2, 8)}`;
+        const taskId =
+          data.taskId ||
+          `task-${Date.now()}-${Math.random().toString(36).slice(2, 8)}`;
         const contextMode =
           data.context_mode === 'group' || data.context_mode === 'isolated'
             ? data.context_mode
@@ -325,6 +327,70 @@ export async function processTaskIpc(
       }
       break;
 
+    case 'update_task':
+      if (data.taskId) {
+        const task = getTaskById(data.taskId);
+        if (!task) {
+          logger.warn(
+            { taskId: data.taskId, sourceGroup },
+            'Task not found for update',
+          );
+          break;
+        }
+        if (!isMain && task.group_folder !== sourceGroup) {
+          logger.warn(
+            { taskId: data.taskId, sourceGroup },
+            'Unauthorized task update attempt',
+          );
+          break;
+        }
+
+        const updates: Parameters<typeof updateTask>[1] = {};
+        if (data.prompt !== undefined) updates.prompt = data.prompt;
+        if (data.schedule_type !== undefined)
+          updates.schedule_type = data.schedule_type as
+            | 'cron'
+            | 'interval'
+            | 'once';
+        if (data.schedule_value !== undefined)
+          updates.schedule_value = data.schedule_value;
+
+        // Recompute next_run if schedule changed
+        if (data.schedule_type || data.schedule_value) {
+          const updatedTask = {
+            ...task,
+            ...updates,
+          };
+          if (updatedTask.schedule_type === 'cron') {
+            try {
+              const interval = CronExpressionParser.parse(
+                updatedTask.schedule_value,
+                { tz: TIMEZONE },
+              );
+              updates.next_run = interval.next().toISOString();
+            } catch {
+              logger.warn(
+                { taskId: data.taskId, value: updatedTask.schedule_value },
+                'Invalid cron in task update',
+              );
+              break;
+            }
+          } else if (updatedTask.schedule_type === 'interval') {
+            const ms = parseInt(updatedTask.schedule_value, 10);
+            if (!isNaN(ms) && ms > 0) {
+              updates.next_run = new Date(Date.now() + ms).toISOString();
+            }
+          }
+        }
+
+        updateTask(data.taskId, updates);
+        logger.info(
+          { taskId: data.taskId, sourceGroup, updates },
+          'Task updated via IPC',
+        );
+      }
+      break;
+
     case 'refresh_groups':
       // Only main group can request a refresh
       if (isMain) {