Never roll back an ambiguous broadcast as if it had been refused (B-76, TX-04, TX-05, TX-20, TX-21, BET-16, BET-17, BET-23, WDR-11, WDR-12, WDR-16, API-13)

place_bet and request_withdrawal released everything on any exception from the
broadcast, including the 15s timeout and a connection dropped after the write. The
tx may have propagated: a bet's sats landed in the pool with no participant, a
withdrawal left while its row said failed and its coins were spendable again.

- client: ElectrumRpcError (subclass of ElectrumError) is raised only for a reply
  carrying a JSON-RPC `error`; timeouts, drops and write errors stay plain
  ElectrumError.
- tx/outcome.py:broadcast_with_verdict sorts a broadcast into accepted / refused /
  uncertain. A refusal is verified first: ElectrumListener.transaction_known asks
  blockchain.transaction.get of the active server and every other one (10s each) —
  any server returning the tx means accepted; the active server plus
  MIN_QUORUM_RESPONSES others all denying it means refused (ALLOW_NO_QUORUM keeps
  the reduced rule); too few answers is uncertain. "already known" wording is only a
  shortcut that skips the check. With no network to ask, a refusal is uncertain.
- place_bet / request_withdrawal / _trigger_payout use it: only a verified refusal
  releases; uncertain leaves the rows building for the reconciler, publishes SSE and
  POST /bets and POST /withdrawals answer 202 with status building; "already known"
  promotes a payout (payout_sent) like any accepted broadcast.
- An accepted transaction is fanned out to every other server
  (ElectrumListener.fan_out_transaction, best effort, off the caller's path). The RBF
  replacement in bump_fee is left for B-77, which rewrites that function.

Tests changed because the spec changed: the existing "refused broadcast" tests raised
a bare RuntimeError (now an uncertain outcome) and are made explicit refusals
(rpc_error) with a network that denies the tx; direct route calls pass a Response;
FakePayoutListener gains the network surface.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

tests/unit/test_scheduler.py

@@ -7,6 +7,7 @@ from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
 
 from app.config import settings
 from app.db.base import Base
+from tests.unit.fake_network import FakeNetwork
 from app.db.models import AuditLog, PendingTransaction, Round, RoundConfig, RoundParticipant, User
 from app.rounds.scheduler import RoundScheduler, _reserved_payout_outpoints
 from app.wallet.hd import derive_pool_address
@@ -87,8 +88,12 @@ class FakePayoutClient:
         return "network-txid"
 
 
-class FakePayoutListener:
-    def __init__(self, client):
+class FakePayoutListener(FakeNetwork):
+    """The listener as the scheduler sees it: the active `client`, plus the network
+    surface a broadcast verdict uses (B-76)."""
+
+    def __init__(self, client, known: bool | None = False):
+        super().__init__(known=known)
         self.client = client