add runtime adapters, scheduler, reconciler, and their unit tests

agent/nix_builder_autoscaler/state_db.py

@@ -153,6 +153,47 @@ class StateDB:
             self._conn.execute("ROLLBACK")
             raise
 
+    def update_slot_fields(self, slot_id: str, **fields: object) -> None:
+        """Update specific slot columns without changing state or last_state_change.
+
+        Uses BEGIN IMMEDIATE. Allowed fields: instance_id, instance_ip,
+        instance_launch_time, lease_count, cooldown_until, interruption_pending.
+        """
+        allowed = {
+            "instance_id",
+            "instance_ip",
+            "instance_launch_time",
+            "lease_count",
+            "cooldown_until",
+            "interruption_pending",
+        }
+        if not fields:
+            return
+
+        set_parts: list[str] = []
+        params: list[object] = []
+        for k, v in fields.items():
+            if k not in allowed:
+                msg = f"Unknown slot field: {k}"
+                raise ValueError(msg)
+            set_parts.append(f"{k} = ?")
+            params.append(v)
+
+        params.append(slot_id)
+        sql = f"UPDATE slots SET {', '.join(set_parts)} WHERE slot_id = ?"
+
+        self._conn.execute("BEGIN IMMEDIATE")
+        try:
+            self._conn.execute(sql, params)
+            self._record_event_inner(
+                "slot_fields_updated",
+                {"slot_id": slot_id, **fields},
+            )
+            self._conn.execute("COMMIT")
+        except Exception:
+            self._conn.execute("ROLLBACK")
+            raise
+
     # -- Reservation operations ---------------------------------------------
 
     def create_reservation(