feat(backend): c2 poll-on-read + output mapping (sprint 8 M3)

- adapter.py: add completed_at field to C2TaskStatus dataclass
- mythic.py: implement get_task() (GraphQL task query) and
  get_task_output() (response query + decode_response_text concat)
- fake.py: deterministic state progression via per-instance call counter;
  get_task_output raises C2Error until completed
- mapping.py: apply_task_to_simulation() idempotent output mapper
  (mapping_applied anchor prevents double-writes)
- migration 0007: add mapping_applied BOOLEAN NOT NULL DEFAULT false to c2_task
- c2_task model: mapping_applied column added
- api/c2.py: GET /api/simulations/<id>/c2/tasks poll-on-read endpoint;
  refreshes incomplete tasks from C2, fetches output on completion,
  applies mapping, skips re-polling for completed tasks; best-effort
  (C2Error on individual task skipped, returns 200 with stale status)
- 51 new tests (396 total); pytest/ruff/mypy all green

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

backend/app/api/c2.py

@@ -21,6 +21,7 @@ from backend.app.models.c2_task import C2Task, C2TaskSource
 from backend.app.models.simulation import Simulation, SimulationStatus
 from backend.app.services.c2.adapter import C2Error
 from backend.app.services.c2.factory import get_adapter
+from backend.app.services.c2.mapping import apply_task_to_simulation
 from backend.app.services.crypto import C2Disabled, decrypt, encrypt
 from backend.app.services.simulation_workflow import promote_to_in_progress
 
@@ -297,3 +298,72 @@ def execute_simulation(sid: int):
             for t in created_tasks
         ]
     }), 200
+
+
+# ---------------------------------------------------------------------------
+# M3 — poll-on-read task listing
+# ---------------------------------------------------------------------------
+
+
+@sims_c2_bp.get("/<int:sid>/c2/tasks")
+@role_required("admin", "redteam")
+def list_simulation_tasks(sid: int):
+    guard = _crypto_guard()
+    if guard is not None:
+        return guard
+
+    sim = db.session.get(Simulation, sid)
+    if sim is None:
+        return jsonify({"error": "Simulation not found"}), 404
+
+    engagement = db.session.get(Engagement, sim.engagement_id)
+    if engagement is None:
+        return jsonify({"error": "Engagement not found"}), 404
+
+    adapter, err = _load_adapter_for_engagement(engagement)
+    if err is not None:
+        return err
+
+    tasks: list[C2Task] = C2Task.query.filter_by(simulation_id=sid).all()
+
+    for task in tasks:
+        if task.completed:
+            continue
+
+        try:
+            status = adapter.get_task(task.mythic_task_display_id)
+        except C2Error:
+            # Best-effort refresh — skip this task if the adapter fails.
+            continue
+
+        task.status = status.status
+        task.completed = status.completed
+
+        if status.completed:
+            task.completed_at = status.completed_at or datetime.now(UTC)
+            try:
+                task.output = adapter.get_task_output(task.mythic_task_display_id)
+            except C2Error:
+                task.output = ""
+            apply_task_to_simulation(task, sim)
+
+    db.session.commit()
+
+    return jsonify({
+        "tasks": [
+            {
+                "id": t.id,
+                "mythic_task_display_id": t.mythic_task_display_id,
+                "callback_display_id": t.callback_display_id,
+                "command": t.command,
+                "params": t.params,
+                "status": t.status,
+                "completed": t.completed,
+                "output": t.output,
+                "mapping_applied": t.mapping_applied,
+                "created_at": t.created_at.isoformat() if t.created_at else None,
+                "completed_at": t.completed_at.isoformat() if t.completed_at else None,
+            }
+            for t in tasks
+        ]
+    }), 200