feat: add basic QEMU and task vertical slice

app/tasks/qemu.py

@@ -0,0 +1,43 @@
+"""Worker semantics for asynchronous QEMU transitions."""
+
+from __future__ import annotations
+
+import json
+import uuid
+
+from app.simulation.clock import Clock
+from app.simulation.transitions import VmState, plan_transition
+from app.tasks.repository import Task, TaskRepository
+from app.tasks.worker import TaskHandler
+
+
+def qemu_handler(repository: TaskRepository, clock: Clock) -> TaskHandler:
+    async def execute(task: Task) -> dict[str, str]:
+        operation = task.task_type.removeprefix("qemu-")
+        resource_id = uuid.UUID(str(task.payload["resource_id"]))
+        async with repository.pool.acquire() as connection:
+            row = await connection.fetchrow("SELECT state FROM resources WHERE id=$1", resource_id)
+            if row is None:
+                raise ValueError("resource disappeared")
+            raw = row["state"]
+            state = json.loads(raw) if isinstance(raw, str) else dict(raw)
+            transition = plan_transition(VmState(str(state["status"])), operation)
+            state["status"] = transition.intermediate
+            await connection.execute(
+                "UPDATE resources SET state=$2::jsonb WHERE id=$1",
+                resource_id,
+                json.dumps(state),
+            )
+        await repository.append_log(task.id, f"VM {operation} started")
+        await clock.sleep(1.0)
+        async with repository.pool.acquire() as connection:
+            state["status"] = transition.after
+            await connection.execute(
+                "UPDATE resources SET state=$2::jsonb WHERE id=$1",
+                resource_id,
+                json.dumps(state),
+            )
+        await repository.append_log(task.id, f"VM {operation} completed")
+        return {"status": str(transition.after)}
+
+    return execute

app/tasks/repository.py

@@ -178,6 +178,18 @@ class TaskRepository:
         row = await self.pool.fetchrow("SELECT * FROM tasks WHERE id=$1", task_id)
         return _task(row) if row is not None else None
 
+    async def get_by_upid(self, upid: str) -> Task | None:
+        row = await self.pool.fetchrow("SELECT * FROM tasks WHERE upid=$1", upid)
+        return _task(row) if row is not None else None
+
+    async def list_for_node(self, node: str) -> tuple[Task, ...]:
+        rows = await self.pool.fetch(
+            """SELECT * FROM tasks WHERE payload->>'node'=$1
+            ORDER BY created_at DESC LIMIT 1000""",
+            node,
+        )
+        return tuple(_task(row) for row in rows)
+
     async def logs(self, task_id: uuid.UUID) -> tuple[str, ...]:
         rows = await self.pool.fetch(
             "SELECT message FROM task_logs WHERE task_id=$1 ORDER BY sequence", task_id