fix(TaskRequest): retain completed tasks to prevent false stop_task failures

Introduce a `completed_tasks` map alongside `loader_tasks` so that tasks
are never silently dropped after completion. Previously, calling
`get_task_result()` removed the task from `loader_tasks`, causing a
subsequent `stop_task()` call to return `{"status": false, "error": "Task X
does not exists"}` — logged as CRITICAL in TAF even when the load succeeded.

Changes:
- `get_task_result()`: moves task from loader_tasks → completed_tasks
  instead of discarding; also checks completed_tasks via getOrDefault so it
  works when stop_task was called first
- `stop_task()`: moves task from loader_tasks → completed_tasks after
  stop_load(); falls back to completed_tasks lookup to return true when task
  was already consumed by get_task_result()
- `reset_task_manager()`: clears completed_tasks alongside loader_tasks to
  prevent stale task-name collisions across test runs

Author: ashwin2002

.agents/profiles/CBRestLoader.md

@@ -94,6 +94,58 @@ sequenceDiagram
 
     C->>TM: /get_task_result
 
+### Task Lifecycle & Cleanup Flow
+
+`loader_tasks` and `completed_tasks` are the two `ConcurrentHashMap`s in `TaskRequest` that track task state.
+Tasks are added to `loader_tasks` on `doc_load`, then transition based on which completion path is taken.
+
+**Path A — `get_task_result()` called before `stop_task()`**
+```
+doc_load  ──► loader_tasks.put(taskName, task)
+               │
+submit_task ──► taskManager.submit(task) ──► task runs ──► "Task_X is completed!" (log)
+               │
+get_task_result()
+  ├─► taskManager.getTaskResult(task)     (waits for future)
+  ├─► loader_tasks.remove(taskName)
+  └─► completed_tasks.put(taskName, task)
+               │
+stop_task()
+  ├─► loader_tasks.get()       → null
+  ├─► completed_tasks.contains → true
+  └─► status: true  ✓
+```
+
+**Path B — `stop_task()` called before `get_task_result()`**
+```
+doc_load  ──► loader_tasks.put(taskName, task)
+               │
+submit_task ──► taskManager.submit(task) ──► task runs
+               │
+stop_task()
+  ├─► task.stop_load()                    (sets flag, run loop exits)
+  ├─► loader_tasks.remove(taskName)
+  └─► completed_tasks.put(taskName, task)
+               │
+get_task_result()
+  ├─► loader_tasks.getOrDefault(taskName, completed_tasks.get(taskName))
+  │                                        (finds task in completed_tasks)
+  ├─► taskManager.getTaskResult(task)
+  └─► failures + status returned  ✓
+```
+
+**Reset**
+```
+reset_task_manager()
+  ├─► loader_tasks    = new ConcurrentHashMap()
+  └─► completed_tasks = new ConcurrentHashMap()   (prevents stale name collisions across test runs)
+```
+
+**Why `completed_tasks` exists:**
+Without it, `stop_task` called after `get_task_result` (or vice versa) hits a missing key in `loader_tasks`
+and returns `{"status": false, "error": "Task X does not exists"}` — logged as CRITICAL in TAF
+even though the task completed successfully.
+
 ### Performance Optimization Guidelines
 * **Multi-Collection Strategy**: Prefer bucket-level clients with dynamic collection switching over per-collection client instances. Workers should call `selectCollection()` dynamically per operation instead of creating dedicated clients per collection.
 * **Shared Cluster Management**: Use `SharedClusterManager` for all multi-collection workloads. It provides:

CLAUDE.md

@@ -0,0 +1 @@
+READ @AGENTS.md

src/main/java/RestServer/TaskRequest.java

@@ -46,6 +46,7 @@ public class TaskRequest {
     static ArrayList<Server> known_servers = new ArrayList<Server>();
     static Object lock_obj = new Object();
     static private ConcurrentHashMap<String, WorkLoadGenerate> loader_tasks = new ConcurrentHashMap<String, WorkLoadGenerate>();
+    static private ConcurrentHashMap<String, WorkLoadGenerate> completed_tasks = new ConcurrentHashMap<String, WorkLoadGenerate>();
     static private ConcurrentHashMap<String, mongo.loadgen.WorkLoadGenerate> mongo_loader_tasks = new ConcurrentHashMap<String, mongo.loadgen.WorkLoadGenerate>();
 
     // Consumed by init_task_manager()
@@ -495,6 +496,7 @@ public ResponseEntity<Map<String, Object>> reset_task_manager() {
         this.shutdown_taskmanager();
         this.init_taskmanager();
         TaskRequest.loader_tasks = new ConcurrentHashMap<String, WorkLoadGenerate>();
+        TaskRequest.completed_tasks = new ConcurrentHashMap<String, WorkLoadGenerate>();
         body.put("status", true);
         return new ResponseEntity<>(body, HttpStatus.OK);
     }
@@ -563,7 +565,8 @@ public ResponseEntity<Map<String, Object>> get_task_result_mongo() {
 
     public ResponseEntity<Map<String, Object>> get_task_result() {
         Map<String, Object> body = new HashMap<>();
-        WorkLoadGenerate task = TaskRequest.loader_tasks.get(this.taskName);
+        WorkLoadGenerate task = TaskRequest.loader_tasks.getOrDefault(this.taskName,
+                TaskRequest.completed_tasks.get(this.taskName));
         if (task != null) {
             Map<String, Object> failures = new HashMap<>();
             boolean okay = false;
@@ -573,6 +576,7 @@ public ResponseEntity<Map<String, Object>> get_task_result() {
                 body.put("error", "Exception during getTaskResult: " + e.toString());
             }
             TaskRequest.loader_tasks.remove(this.taskName);
+            TaskRequest.completed_tasks.put(this.taskName, task);
             for (HashMap.Entry<String, List<Result>> optype : task.failedMutations.entrySet()) {
                 optype.getValue().forEach(
                         (failed_result) -> {
@@ -602,6 +606,10 @@ public ResponseEntity<Map<String, Object>> stop_task() {
         WorkLoadGenerate task = TaskRequest.loader_tasks.get(this.taskName);
         if (task != null) {
             task.stop_load();
+            TaskRequest.loader_tasks.remove(this.taskName);
+            TaskRequest.completed_tasks.put(this.taskName, task);
+            body.put("status", true);
+        } else if (TaskRequest.completed_tasks.containsKey(this.taskName)) {
             body.put("status", true);
         } else {
             body.put("error", "Task " + this.taskName + " does not exists");