feat(backend): c2 callback history + task import (sprint 8 M4)

Command source decision: extended C2TaskStatus with command: str | None
(default None). Added command_name to _GET_TASK_QUERY so get_task() returns
command in a single round-trip — no separate history fetch needed on import.
4-line change, zero cascading test impact.

adapter.py:
- C2TaskStatus: add command: str | None = None field
- C2HistoricalTask: new dataclass (display_id, command, params, status,
  completed, timestamp) for history rows
- C2TaskPage.items: typed as list[C2HistoricalTask] (was list[dict])

mythic.py:
- _GET_TASK_QUERY: add command_name field
- _LIST_CALLBACK_TASKS_QUERY: new query (order_by id desc, limit/offset)
- _COUNT_CALLBACK_TASKS_QUERY: new aggregate query for total
- get_task(): surfaces command_name as status.command
- list_callback_tasks(): two _post() calls (tasks + count), allow_redirects=False

fake.py:
- _FAKE_HISTORY: frozen deterministic history (cb1=12, cb2=0, cb3=5 tasks)
- list_callback_tasks(): serves from _FAKE_HISTORY, pagination applied
- get_task(): returns command from _tasks dict

api/c2.py:
- GET /api/engagements/<eid>/c2/callbacks/<cid>/history: page+page_size
  defaults 1/25, cap 100, reject <1, 502 on adapter error
- POST /api/simulations/<sid>/c2/import: idempotent per (sim,mythic_id) pair,
  source=import, completed tasks get output+mapping_applied, incomplete tasks
  stored for poll-on-read pickup, auto-transition pending→in_progress

60 new tests (456 total); pytest/ruff/mypy all green

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

backend/tests/test_c2_adapter_mythic_m4.py

@@ -0,0 +1,167 @@
+"""MythicAdapter M4 tests — list_callback_tasks, mocked HTTP."""
+from __future__ import annotations
+
+import pytest
+import requests
+import requests_mock as rm_module
+
+from backend.app.services.c2.adapter import C2Error, C2HistoricalTask
+from backend.app.services.c2.mythic import MythicAdapter
+
+_BASE_URL = "https://mythic.lab:7443"
+_GQL_URL = _BASE_URL + "/graphql"
+_TOKEN = "fake-api-token"
+
+
+@pytest.fixture()
+def adapter():
+    return MythicAdapter(url=_BASE_URL, api_token=_TOKEN, verify_tls=False)
+
+
+def _task_list_payload(tasks: list[dict]) -> dict:
+    return {"data": {"task": tasks}}
+
+
+def _count_payload(count: int) -> dict:
+    return {"data": {"task_aggregate": {"aggregate": {"count": count}}}}
+
+
+class TestMythicAdapterListCallbackTasks:
+    def test_returns_tasks_from_graphql(self, adapter):
+        tasks_payload = _task_list_payload([
+            {
+                "display_id": 7,
+                "command_name": "whoami",
+                "params": "",
+                "status": "completed",
+                "completed": True,
+                "timestamp": "2026-06-10T12:00:00Z",
+            }
+        ])
+        count_payload = _count_payload(1)
+
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, [{"json": tasks_payload}, {"json": count_payload}])
+            page = adapter.list_callback_tasks(callback_display_id=1, page=1, page_size=25)
+
+        assert page.total == 1
+        assert len(page.items) == 1
+        item = page.items[0]
+        assert isinstance(item, C2HistoricalTask)
+        assert item.display_id == 7
+        assert item.command == "whoami"
+        assert item.completed is True
+
+    def test_pagination_offset_calculation(self, adapter):
+        """page=2, page_size=10 → offset=10 must be sent to Mythic."""
+        tasks_payload = _task_list_payload([])
+        count_payload = _count_payload(0)
+
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, [{"json": tasks_payload}, {"json": count_payload}])
+            adapter.list_callback_tasks(callback_display_id=1, page=2, page_size=10)
+
+            # First request is the task list; check variables.
+            first_body = m.request_history[0].json()
+            variables = first_body.get("variables", {})
+
+        assert variables.get("offset") == 10
+        assert variables.get("limit") == 10
+
+    def test_sends_apitoken_header(self, adapter):
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, [
+                {"json": _task_list_payload([])},
+                {"json": _count_payload(0)},
+            ])
+            adapter.list_callback_tasks(callback_display_id=1)
+            for req in m.request_history:
+                assert req.headers.get("apitoken") == _TOKEN
+
+    def test_empty_task_list(self, adapter):
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, [
+                {"json": _task_list_payload([])},
+                {"json": _count_payload(0)},
+            ])
+            page = adapter.list_callback_tasks(callback_display_id=1)
+
+        assert page.total == 0
+        assert page.items == []
+
+    def test_network_error_raises_c2error(self, adapter):
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, exc=requests.exceptions.ConnectionError("refused"))
+            with pytest.raises(C2Error):
+                adapter.list_callback_tasks(callback_display_id=1)
+
+    def test_http_error_raises_c2error(self, adapter):
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, status_code=500, text="error")
+            with pytest.raises(C2Error):
+                adapter.list_callback_tasks(callback_display_id=1)
+
+    def test_no_redirect_followed(self, adapter):
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, status_code=301, headers={"Location": "https://evil.example/"})
+            with pytest.raises(C2Error):
+                adapter.list_callback_tasks(callback_display_id=1)
+            # Both requests (tasks + count) should each only make one attempt.
+            for req in m.request_history:
+                assert req.method == "POST"
+
+    def test_page_and_page_size_in_response(self, adapter):
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, [
+                {"json": _task_list_payload([])},
+                {"json": _count_payload(50)},
+            ])
+            page = adapter.list_callback_tasks(callback_display_id=1, page=3, page_size=10)
+
+        assert page.page == 3
+        assert page.page_size == 10
+        assert page.total == 50
+
+
+class TestMythicAdapterGetTaskCommandField:
+    """Ensure command_name is surfaced via get_task() C2TaskStatus.command."""
+
+    def test_get_task_returns_command(self, adapter):
+        payload = {
+            "data": {
+                "task": [
+                    {
+                        "display_id": 7,
+                        "command_name": "shell",
+                        "status": "completed",
+                        "completed": True,
+                        "timestamp": "2026-06-10T12:00:00Z",
+                    }
+                ]
+            }
+        }
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, json=payload)
+            status = adapter.get_task(7)
+
+        assert status.command == "shell"
+
+    def test_get_task_command_none_when_missing(self, adapter):
+        payload = {
+            "data": {
+                "task": [
+                    {
+                        "display_id": 7,
+                        "command_name": None,
+                        "status": "submitted",
+                        "completed": False,
+                        "timestamp": None,
+                    }
+                ]
+            }
+        }
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, json=payload)
+            status = adapter.get_task(7)
+
+        assert status.command is None