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/tests/test_c2_adapter_mythic_m3.py

@@ -0,0 +1,188 @@
+"""MythicAdapter M3 tests — get_task and get_task_output, mocked HTTP."""
+from __future__ import annotations
+
+import pytest
+import requests
+import requests_mock as rm_module
+
+from backend.app.services.c2.adapter import C2Error
+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)
+
+
+class TestMythicAdapterGetTask:
+    def test_returns_status_for_incomplete_task(self, adapter):
+        payload = {
+            "data": {
+                "task": [
+                    {
+                        "display_id": 7,
+                        "status": "processing",
+                        "completed": False,
+                        "timestamp": None,
+                    }
+                ]
+            }
+        }
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, json=payload)
+            status = adapter.get_task(7)
+
+        assert status.display_id == 7
+        assert status.status == "processing"
+        assert status.completed is False
+        assert status.completed_at is None
+
+    def test_returns_completed_at_for_completed_task(self, adapter):
+        payload = {
+            "data": {
+                "task": [
+                    {
+                        "display_id": 7,
+                        "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.completed is True
+        assert status.completed_at is not None
+        assert status.completed_at.year == 2026
+
+    def test_raises_when_task_not_found(self, adapter):
+        payload = {"data": {"task": []}}
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, json=payload)
+            with pytest.raises(C2Error, match="not found"):
+                adapter.get_task(999)
+
+    def test_sends_apitoken_header(self, adapter):
+        payload = {
+            "data": {
+                "task": [
+                    {"display_id": 1, "status": "submitted", "completed": False, "timestamp": None}
+                ]
+            }
+        }
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, json=payload)
+            adapter.get_task(1)
+            assert m.last_request.headers.get("apitoken") == _TOKEN
+
+    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.get_task(1)
+
+    def test_no_redirect_followed(self, adapter):
+        """get_task must not follow HTTP redirects."""
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, status_code=301, headers={"Location": "https://evil.example/"})
+            with pytest.raises(C2Error):
+                adapter.get_task(1)
+            assert len(m.request_history) == 1
+
+    def test_invalid_timestamp_does_not_crash(self, adapter):
+        """A malformed timestamp field falls back to completed_at=None without raising."""
+        payload = {
+            "data": {
+                "task": [
+                    {
+                        "display_id": 5,
+                        "status": "completed",
+                        "completed": True,
+                        "timestamp": "not-a-date",
+                    }
+                ]
+            }
+        }
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, json=payload)
+            status = adapter.get_task(5)
+
+        assert status.completed is True
+        assert status.completed_at is None
+
+
+class TestMythicAdapterGetTaskOutput:
+    def test_returns_decoded_output(self, adapter):
+        import base64
+        encoded = base64.b64encode(b"Administrator\r\n").decode()
+        payload = {
+            "data": {
+                "response": [{"response_text": encoded}]
+            }
+        }
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, json=payload)
+            output = adapter.get_task_output(7)
+
+        assert "Administrator" in output
+
+    def test_concatenates_multiple_responses(self, adapter):
+        import base64
+        r1 = base64.b64encode(b"line one\n").decode()
+        r2 = base64.b64encode(b"line two\n").decode()
+        payload = {
+            "data": {
+                "response": [{"response_text": r1}, {"response_text": r2}]
+            }
+        }
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, json=payload)
+            output = adapter.get_task_output(7)
+
+        assert "line one" in output
+        assert "line two" in output
+
+    def test_returns_empty_string_when_no_responses(self, adapter):
+        payload = {"data": {"response": []}}
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, json=payload)
+            output = adapter.get_task_output(7)
+
+        assert output == ""
+
+    def test_skips_empty_response_text(self, adapter):
+        import base64
+        encoded = base64.b64encode(b"real output").decode()
+        payload = {
+            "data": {
+                "response": [
+                    {"response_text": ""},
+                    {"response_text": encoded},
+                ]
+            }
+        }
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, json=payload)
+            output = adapter.get_task_output(7)
+
+        assert output == "real output"
+
+    def test_network_error_raises_c2error(self, adapter):
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, exc=requests.exceptions.Timeout("timeout"))
+            with pytest.raises(C2Error):
+                adapter.get_task_output(7)
+
+    def test_no_redirect_followed(self, adapter):
+        with rm_module.Mocker() as m:
+            m.post(_GQL_URL, status_code=302, headers={"Location": "https://evil.example/"})
+            with pytest.raises(C2Error):
+                adapter.get_task_output(1)
+            assert len(m.request_history) == 1