Abandon a transaction only on proof, and keep watching failed rows (B-78, TX-15, TX-17, TX-23, TX-26, ELC-28, DAT-33, DAT-36, DAT-69, DAT-72, AUD-11, AUD-12, AUD-31, AUD-39, API-32)

reconcile_once abandoned a row when the *active* server's history lacked its txid:
after 120s for `building` (which a restart onto a different server makes likely),
after 6h for `pending`, and all at once after a forward clock jump. It re-checked the
status but not the txid, so it raced the bumper, and a `failed` row was never looked at
again.

- The reconciler asks every server (ElectrumListener.get_histories, active + others) for
  the history of the row's address and looks for every txid of the row. Present on any
  server -> promoted (adopting the version found). Absent is only "no server of the
  quorum knows it" and needs the active server plus the quorum minimum of the others to
  have answered; even then nothing is released without proof:
  (a) an input spent in a block by a transaction that is none of the row's versions,
      agreed by a strict majority of a quorum of the other servers (confirmed_spender), or
  (b) a rebroadcast of the latest raw tx to every server (rebroadcast_everywhere)
      refused by all of them, explicitly, for missing/spent inputs.
  Accepted or "already known" by any server means alive; a fee refusal is not proof
  (`building` -> `pending` for the bumper, `pending` untouched); too few answers or
  anything else leaves the row alone. failure_reason names the proof.
- The write re-reads status *and* current_txid under begin_immediate (TX-26).
- pending_transactions.failed_at (set by _abandon and _release_failed_withdrawal) starts
  a 14-day watch: a failed row that a majority of the other servers (at least the quorum
  minimum) list in a block becomes `confirmed`, writes pending_tx_resurrected once and
  pauses the lottery with paused_reason `resurrected_tx`; linked rows are not corrected.
  The confirmation is by quorum of histories for now; merkle proofs come with B-83.
- round_config.paused_reason (migration b7d2e41c9a05, with the failed_at one): `operator`
  from POST /admin/pause (which accepts an optional `note` and never overwrites an
  automatic reason), cleared by resume, which logs the reason it lifted; exposed on
  /admin/config and GET /rounds/current. rounds/pause.py:pause_automatically is the
  system's way in.
- PendingTransactionReconciler takes the listener as `network`; with none it can promote
  but never abandon.

Tests changed because the spec changed: the three reconciler tests that expect an
abandonment (and the one in test_tx_versions) now supply a network that proves the
transaction is gone.

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

docs/adr/ADR-51-dubbio-liberano-mai-fondi.md

@@ -1,6 +1,6 @@
 # ADR-51 — Nel dubbio non si liberano mai i fondi
 
-- **Stato:** Accettata — implementazione da completare (B-78)
+- **Stato:** Accettata
 - **Area:** Denaro in movimento
 - **Fonte di verità per:** la scelta di progetto descritta qui sotto; i requisiti (`PREFISSO-NN`) che la attuano stanno nei documenti di dominio, indicati nelle *Conseguenze*.
 
@@ -36,8 +36,4 @@ pausa la lotteria ([ADR-28](ADR-28-pausa-manutenzione-ferma-round-successivo.md)
   congelato e visibile, mai duplicato.
 
 *Codice:* `app/tx/reconcile.py:reconcile_once` · `app/tx/reconcile.py:_is_due` · `app/bets/service.py:place_bet` · `app/withdrawals/service.py:request_withdrawal` · `app/tx/confirmation.py:poll_once` · `app/tx/broadcast.py:bump_fee` ·
-*Test:* `tests/unit/test_broadcast_outcome.py`
-*Stato:* da implementare (B-78) · *Oggi:* l'abbandono avviene
-quando la cronologia del solo server attivo non contiene alcun txid della
-riga, dopo 120s per `building` e 6 ore per `pending`; le righe `failed` non
-sono più controllate.
+*Test:* `tests/unit/test_broadcast_outcome.py`, `tests/unit/test_tx_versions.py`, `tests/unit/test_reconcile_proof.py`