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>

docs/audit-log.md

@@ -352,9 +352,7 @@ flowchart LR
   200 caratteri. `user_id` sì, `round_id` **no** (a differenza di
   `bet_placed`). Stessa transazione del ripristino.
   *Codice:* `app/bets/service.py:_release_failed_bet` ·
-  *Test:* `tests/unit/test_bets.py`
-  *Stato:* da implementare (B-76) · *Oggi:* scritto per qualunque errore
-  d'invio, compresi timeout e disconnessioni.
+  *Test:* `tests/unit/test_bets.py`, `tests/unit/test_broadcast_outcome.py`
 
 - **[AUD-21]** `withdrawal_sent` — la rete ha accettato la transazione di un
   prelievo. Payload `{"txid", "amount_sent_sats", "external_address"}`:
@@ -373,9 +371,7 @@ flowchart LR
   (`reason` troncato a 200 caratteri). `user_id` sì, `round_id` no. Stessa
   transazione del ripristino.
   *Codice:* `app/withdrawals/service.py:_release_failed_withdrawal` ·
-  *Test:* nessun test verifica la riga di audit.
-  *Stato:* da implementare (B-76) · *Oggi:* scritto per qualunque errore
-  d'invio, compresi timeout e disconnessioni.
+  *Test:* `tests/unit/test_broadcast_outcome.py`
 
 ### Round