feat(ops): track broker balance worker failure lifecycle and backoff

Co-authored-by: genichin <4282227+genichin@users.noreply.github.com>

tests/application/test_snapshot_scheduler.py

@@ -665,3 +665,60 @@ def test_build_kis_reinit_callback_returns_callable_for_kis():
     result(new_cred)
     assert broker._account_ref == "new-acct"
     assert broker._app_key == "new-k"
+
+
+def test_balance_worker_health_isolated_backoff_and_recovery():
+    from trex_core.application.broker_port import BalanceItem, BrokerBalanceError
+    from trex_core.domain.slot import SlotService
+    from trex_core.domain.slot.in_memory_repository import InMemorySlotRepository
+
+    class SequencedBroker(PaperBroker):
+        def __init__(self):
+            super().__init__()
+            self.steps = []
+
+        def get_balance(self):
+            if not self.steps:
+                return []
+            step = self.steps.pop(0)
+            if isinstance(step, Exception):
+                raise step
+            return step
+
+    now = {"t": datetime(2026, 9, 12, 0, 0, tzinfo=timezone.utc)}
+    read = _make_stub()
+    store = SnapshotStore()
+    slot_repo = InMemorySlotRepository()
+    slot_service = SlotService(slot_repo, instance_key="default")
+    slot_repo.reconcile_universe("default", {"pf-X": "X"})
+    broker = SequencedBroker()
+    sched = SnapshotScheduler(
+        read_port=read,
+        store=store,
+        broker=broker,
+        slot_repo=slot_repo,
+        slot_service=slot_service,
+        clock=lambda: now["t"],
+    )
+
+    broker.steps = [BrokerBalanceError("http_5xx"), [BalanceItem("X", 0)]]
+    assert sched.run_once() is True
+    state = sched.balance_worker_health(stale_after_sec=86_400)
+    assert state["position_reconciliation"]["state"] == "unavailable"
+    assert state["position_reconciliation"]["failure_code"] == "http_5xx"
+    assert state["position_reconciliation"]["consecutive_failures"] == 1
+    assert state["core_holding_reconciliation"]["state"] == "ok"
+
+    broker.steps = [[BalanceItem("X", 0)]]
+    assert sched.run_once() is True
+    assert broker.steps == []  # position worker stayed in backoff, core worker still ran
+    state = sched.balance_worker_health(stale_after_sec=86_400)
+    assert state["position_reconciliation"]["consecutive_failures"] == 1
+    assert state["core_holding_reconciliation"]["state"] == "ok"
+
+    now["t"] += timedelta(seconds=16)
+    broker.steps = [[BalanceItem("X", 0)], [BalanceItem("X", 0)]]
+    assert sched.run_once() is True
+    state = sched.balance_worker_health(stale_after_sec=86_400)
+    assert state["position_reconciliation"]["state"] == "ok"
+    assert state["position_reconciliation"]["consecutive_failures"] == 0