Distinguish a pending-only balance from a truly insufficient one (B-37)

request_withdrawal validated against confirmed UTXOs only and answered
a flat insufficient_balance even when the requested amount was covered
by the pending-inclusive balance the UI actually shows (unconfirmed
change from a recent bet/withdrawal) — contradicting what the user was
looking at on screen. Raise balance_pending_confirmation instead when
compute_pending_balance covers the amount, carrying the pending sats
in params, with its error.* string in all 7 languages.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/unit/test_withdrawals.py

@@ -2,6 +2,7 @@ import pytest
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
 
+from app.bets.service import place_bet
 from app.config import settings
 from app.db.base import Base
 from app.db.models import PendingTransaction, User, UtxoEvent, Withdrawal
@@ -99,6 +100,35 @@ async def test_withdrawal_rejects_insufficient_balance(session_factory):
             await request_withdrawal(session, client, user, EXTERNAL_ADDRESS, BET_AMOUNT_SATS)
 
 
+async def test_withdrawal_distinguishes_pending_from_truly_insufficient_balance(session_factory):
+    """B-37: right after a bet, cached_balance_sats is ~0 because the whole funding
+    UTXO was spent as input and the change hasn't confirmed yet — but the UI shows
+    the pending-inclusive balance (compute_pending_balance), which does cover a
+    withdrawal of this size. The error must say "not confirmed yet", not flatly
+    "insufficient balance", or it contradicts what the user is looking at."""
+    user_id = await _make_funded_user(session_factory, 4, 3_000_000_000)
+    bet_client = FakeElectrumClient()
+
+    async with session_factory() as session:
+        user = await session.get(User, user_id)
+        await place_bet(session, bet_client, user)
+
+    async with session_factory() as session:
+        user = await session.get(User, user_id)
+        assert user.cached_balance_sats == 0  # the whole funding UTXO was spent as input
+
+        withdraw_client = FakeElectrumClient()
+        with pytest.raises(WithdrawalError) as exc_info:
+            # Above the withdrawal minimum (BET_AMOUNT_SATS) and covered by the
+            # unconfirmed change (~1_999_800_000 sats), but not by the (zero)
+            # confirmed balance.
+            await request_withdrawal(session, withdraw_client, user, EXTERNAL_ADDRESS, 1_500_000_000)
+
+    assert exc_info.value.code == "balance_pending_confirmation"
+    assert exc_info.value.params["pending_sats"] > 0
+    assert not withdraw_client.broadcasted
+
+
 @pytest.mark.parametrize(
     "address",
     [