Add eval harness (#62 P4), status frames (#96), and agentic runs (#63).

Ship the Phase 4 accuracy eval suite with a manual Gitea workflow, emit
versioned WS status frames during grounded chat, and introduce opt-in
agent infrastructure (Redis/Celery, AgentRun/Step, tools, orchestrator)
gated by ALLOW_AGENTIC_TASKS so default chat behaviour stays unchanged.

llm_be/chat_backend/views_agent.py

@@ -0,0 +1,96 @@
+"""REST API for AgentRun rehydration + cancel (#63)."""
+
+from __future__ import annotations
+
+from django.utils import timezone
+from rest_framework import serializers, status
+from rest_framework.permissions import IsAuthenticated
+from rest_framework.response import Response
+from rest_framework.views import APIView
+
+from chat_backend.models import AgentRun, AgentStep
+
+
+class AgentStepSerializer(serializers.ModelSerializer):
+    class Meta:
+        model = AgentStep
+        fields = (
+            "id",
+            "index",
+            "parent_step",
+            "title",
+            "status",
+            "is_subagent",
+            "tool_name",
+            "tool_input",
+            "tool_output",
+            "error",
+            "started_at",
+            "completed_at",
+            "created",
+        )
+
+
+class AgentRunSerializer(serializers.ModelSerializer):
+    steps = AgentStepSerializer(many=True, read_only=True)
+
+    class Meta:
+        model = AgentRun
+        fields = (
+            "id",
+            "conversation",
+            "goal",
+            "title",
+            "status",
+            "plan",
+            "result",
+            "error",
+            "model_orchestrator",
+            "model_subagent",
+            "tool_call_count",
+            "iteration_count",
+            "cancel_requested",
+            "started_at",
+            "completed_at",
+            "created",
+            "steps",
+        )
+
+
+class AgentRunListView(APIView):
+    permission_classes = [IsAuthenticated]
+
+    def get(self, request):
+        qs = (
+            AgentRun.objects.filter(user=request.user)
+            .prefetch_related("steps")
+            .order_by("-created")[:50]
+        )
+        return Response(AgentRunSerializer(qs, many=True).data)
+
+
+class AgentRunDetailView(APIView):
+    permission_classes = [IsAuthenticated]
+
+    def get(self, request, run_id: int):
+        try:
+            run = AgentRun.objects.prefetch_related("steps").get(
+                pk=run_id, user=request.user
+            )
+        except AgentRun.DoesNotExist:
+            return Response({"detail": "Not found."}, status=status.HTTP_404_NOT_FOUND)
+        return Response(AgentRunSerializer(run).data)
+
+
+class AgentRunCancelView(APIView):
+    permission_classes = [IsAuthenticated]
+
+    def post(self, request, run_id: int):
+        try:
+            run = AgentRun.objects.get(pk=run_id, user=request.user)
+        except AgentRun.DoesNotExist:
+            return Response({"detail": "Not found."}, status=status.HTTP_404_NOT_FOUND)
+        if run.is_terminal:
+            return Response(AgentRunSerializer(run).data)
+        run.mark_cancelled()
+        return Response(AgentRunSerializer(run).data)