bookkeeper: test (failing!) for rebalances on restart.

```
lightningd-1 2025-09-22T02:10:10.978Z **BROKEN** plugin-bookkeeper: Unparsable datastore ["bookkeeper","rebalances","1-2"]
```

And, indeed, rebalance is missing:

```
>       outbound_ev = only_one([ev for ev in inc_evs if ev['tag'] == 'rebalance_fee'])

tests/test_bookkeeper.py:825: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

arr = []

    def only_one(arr):
        """Many JSON RPC calls return an array; often we only expect a single entry
        """
>       assert len(arr) == 1
E       AssertionError

```

Signed-off-by: Rusty Russell <[email protected]>

Author: rustyrussell

tests/test_bookkeeper.py

@@ -760,6 +760,7 @@ def test_empty_node(node_factory, bitcoind):
         l1.rpc.bkpr_inspect('wallet')
 
 
+@pytest.mark.xfail(strict=True)
 def test_rebalance_tracking(node_factory, bitcoind):
     """
     We identify rebalances (invoices paid and received by our node),
@@ -822,6 +823,18 @@ def test_rebalance_tracking(node_factory, bitcoind):
     assert outbound_ev['credit_msat'] == Millisatoshi(0)
     assert outbound_ev['payment_id'] == pay_hash
 
+    # Will reload on restart!
+    l1.restart()
+
+    inc_evs = l1.rpc.bkpr_listincome()['income_events']
+    outbound_chan_id = only_one(l1.rpc.listpeerchannels(l2.info['id'])['channels'])['channel_id']
+
+    outbound_ev = only_one([ev for ev in inc_evs if ev['tag'] == 'rebalance_fee'])
+    assert outbound_ev['account'] == outbound_chan_id
+    assert outbound_ev['debit_msat'] == Millisatoshi(1001)
+    assert outbound_ev['credit_msat'] == Millisatoshi(0)
+    assert outbound_ev['payment_id'] == pay_hash
+
 
 def test_bookkeeper_custom_notifs(node_factory, chainparams):
     # FIXME: what happens if we send internal funds to 'external' wallet?