Check confirmation/existence via scripthash history, not verbose replies (B-41)

poll_once and reconcile.py's existence check both called
blockchain.transaction.get(txid, verbose=True). Several Electrum server
implementations and versions reject the verbose flag outright
("verbose transactions are currently unsupported"), which would have
meant no confirmations and no reconciliation ever running against such
a server, read as a plain transport error. reconcile.py additionally
decided whether to abandon a transaction - releasing its funds - by
substring-matching the error text ("missing", "not found", ...), which
only works against ElectrumX's specific wording.

Both now ask blockchain.scripthash.get_history for the address that
owns every input of the transaction (a user's own address for a
bet/withdrawal, the pool address for a payout) and look for the txid in
the result: present with height > 0 means confirmed, present with
height <= 0 means still in the mempool, absent means the server
doesn't know it. get_history is a plain, universally-supported Electrum
method, and "not in the list" replaces the old substring-matching
entirely - no more guessing at error wording to decide whether to
release funds. History is cached per scripthash within one pass, since
every "payout" row shares the same pool address.

New app/tx/pending_address.py factors out own_address_for (the
address derivation was previously duplicated informally inside
tx/broadcast.py's signing context) so confirmation.py and reconcile.py
share one definition instead of two that could compute different
addresses for the same row.

tests/unit/test_confirmation.py and test_reconcile.py needed real User
rows and a master-key bootstrap they didn't have before, since address
derivation is now exercised for real rather than assumed. Suite grows
from 217 to 222 tests. BUGS.md moves B-41 to Previously fixed - no
Medium-severity finding remains open.

BUGS.md

@@ -1,11 +1,11 @@
 # Known bugs
 
 A second full-codebase audit on 2026-07-27 found **25 further issues** (4 critical, 6 high,
-7 medium, 8 low), listed below as B-41 … B-49. B-25 through B-40 are fixed (see "Previously
-fixed" below) — no Critical-severity finding remains open; the other 9 are Medium/Low.
+7 medium, 8 low), listed below as B-42 … B-49. B-25 through B-41 are fixed (see "Previously
+fixed" below) — no Critical- or Medium-severity finding remains open; the other 8 are Low/hygiene.
 The 139-test suite was green at the time of the audit, so none of these were caught by existing
-coverage — every fix lands with a regression test (the sixteen fixes so far brought the suite
-from 139 to 217).
+coverage — every fix lands with a regression test (the seventeen fixes so far brought the suite
+from 139 to 222).
 
 The recurring pattern across the open findings is worth stating once: the code is rigorous
 about the failure modes that have actually been hit, and silent about the ones that have not.
@@ -16,29 +16,6 @@ admin auth, single-process assumptions, no user-facing history, etc.) are docume
 
 ---
 
-## Medium
-
-### B-41 — Confirmation/reconciliation logic depends on `verbose=True`, which is not universally supported
-
-`poll_once` and `reconcile._tx_exists_on_chain` call `blockchain.transaction.get(txid, True)`.
-Several Electrum server implementations and versions reject the verbose flag ("verbose
-transactions are currently unsupported"). Falling back onto such a server means **no
-confirmations, no reconciliation** — and the code would read that as a transport error and stay
-silent. (`bump_fee`'s own `verbose=True` call was removed as part of the B-40 fix — it now reads
-the raw transaction and parses the output value with `embit` instead, so bumps are unaffected by
-this finding.)
-
-Related: `reconcile.py:83` decides whether to **abandon a transaction** by substring-matching
-the error text (`"missing"`, `"not found"`, `"no such"`, `"unknown"`). It works against
-ElectrumX; it is fragile as the basis for a decision that releases funds.
-
-**Proposed fix.** Use `blockchain.transaction.get_merkle` (or the scripthash history) for
-confirmation and existence checks — both are portable and give the confirming height directly.
-Probe verbose support once at connect time and record it on the client, so an unsupported
-server is detected loudly at session start rather than silently mid-operation.
-
----
-
 ## Low / hygiene
 
 ### B-42 — `/docs` exposed in production
@@ -121,9 +98,10 @@ already does.
 - **B-38** — the SSE subscriber cap was global, so one client opening enough connections degraded every other user to polling
 - **B-39** — SQLite ran without WAL or a `busy_timeout`, so a writer could block every reader and a second writer failed immediately instead of waiting
 - **B-40** — `bump_fee` held a DB session open across N slow network calls, and computed a prevout's value from a server-reported float instead of an exact integer
+- **B-41** — confirmation/reconciliation depended on a verbose `blockchain.transaction.get` reply many Electrum servers reject, and abandonment relied on fragile substring-matching of an error message
 
 See git history for the fix-by-fix breakdown (commits `f13f685`, `50a43ae`, `933760e`, and the
-B-28/B-29/B-30/B-31/B-32/B-33/B-34/B-35/B-36/B-37/B-38/B-39/B-40 fixes). Suite grew from 139 to 217 tests over the sixteen.
+B-28/B-29/B-30/B-31/B-32/B-33/B-34/B-35/B-36/B-37/B-38/B-39/B-40/B-41 fixes). Suite grew from 139 to 222 tests over the seventeen.
 
 A full-codebase audit on 2026-07-26 (commit `d4e0974`) found 24 bugs across every Python
 module under `app/`, both static frontends, and the Docker/Caddy deployment — 5 critical,

app/electrum/client.py

@@ -169,6 +169,17 @@ class ElectrumClient:
     async def listunspent(self, scripthash: str) -> list[dict]:
         return await self.request("blockchain.scripthash.listunspent", [scripthash])
 
+    async def get_history(self, scripthash: str) -> list[dict]:
+        """Every transaction touching `scripthash`, each as {"tx_hash", "height"} —
+        height > 0 means confirmed at that height, height <= 0 means still in the
+        mempool. Used instead of blockchain.transaction.get's verbose=True mode
+        for confirmation/existence checks (B-41): several Electrum server
+        implementations and versions reject the verbose flag outright ("verbose
+        transactions are currently unsupported"), while get_history is a plain,
+        universally-supported method every server must implement.
+        """
+        return await self.request("blockchain.scripthash.get_history", [scripthash])
+
     async def broadcast(self, raw_tx_hex: str) -> str:
         return await self.request("blockchain.transaction.broadcast", [raw_tx_hex])
 

app/tx/confirmation.py

@@ -7,7 +7,9 @@ from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker
 
 from app.db.models import PendingTransaction
 from app.electrum.client import ElectrumClient
+from app.electrum.scripthash import address_to_scripthash
 from app.rounds.events import broadcaster
+from app.tx.pending_address import own_address_for
 
 logger = logging.getLogger(__name__)
 
@@ -31,24 +33,52 @@ async def poll_once(session_factory: async_sessionmaker, client: ElectrumClient)
         candidates = (
             await session.execute(
                 select(
-                    PendingTransaction.id, PendingTransaction.current_txid, PendingTransaction.kind
+                    PendingTransaction.id,
+                    PendingTransaction.current_txid,
+                    PendingTransaction.kind,
+                    PendingTransaction.user_id,
                 ).where(PendingTransaction.status == "pending")
             )
         ).all()
 
+        # Resolved once per candidate while the session is still open, and cached
+        # by scripthash below — every "payout" row shares the same pool address,
+        # so this also avoids asking the server the same history twice per tick.
+        scripthash_by_id: dict[int, str] = {}
+        for pending_id, _txid, kind, user_id in candidates:
+            try:
+                address = await own_address_for(session, kind, user_id)
+                scripthash_by_id[pending_id] = address_to_scripthash(address)
+            except Exception:
+                logger.exception("could not derive the address for pending_transaction %s", pending_id)
+
     confirmed = 0
-    for pending_id, txid, kind in candidates:
+    history_cache: dict[str, list[dict]] = {}
+    for pending_id, txid, kind, _user_id in candidates:
+        scripthash = scripthash_by_id.get(pending_id)
+        if scripthash is None:
+            continue  # address derivation failed above; already logged
+
         try:
-            tx = await client.get_transaction(txid, verbose=True)
+            if scripthash not in history_cache:
+                history_cache[scripthash] = await client.get_history(scripthash)
         except Exception:
-            # One unresolvable txid must not stop the others: a tx the server no
-            # longer knows (dropped from the mempool, replaced) used to abort the
-            # whole pass, so nothing confirmed again until an operator intervened
-            # (B-03). Abandoning such a row is app/tx/reconcile.py's job, not ours.
-            logger.warning("could not check pending_transaction %s (txid %s)", pending_id, txid, exc_info=True)
+            # One unresolvable scripthash must not stop the others: a tx the server
+            # no longer knows about (dropped from the mempool, replaced) used to
+            # abort the whole pass via a verbose blockchain.transaction.get call
+            # that some servers reject outright (B-41), so nothing confirmed again
+            # until an operator intervened (B-03). Abandoning such a row is
+            # app/tx/reconcile.py's job, not ours.
+            logger.warning("could not fetch history for pending_transaction %s (txid %s)", pending_id, txid, exc_info=True)
             continue
-        if not tx or tx.get("confirmations", 0) < 1:
+
+        entry = next((e for e in history_cache[scripthash] if e.get("tx_hash") == txid), None)
+        # height > 0 means confirmed at that height; 0 or absent means still in
+        # the mempool (or the server doesn't know this txid at all yet) — either
+        # way, not confirmed, so keep waiting.
+        if entry is None or entry.get("height", 0) <= 0:
             continue
+
         async with session_factory() as session:
             row = await session.get(PendingTransaction, pending_id)
             if row is None or row.status != "pending":

app/tx/pending_address.py

@@ -0,0 +1,22 @@
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.db.models import User
+from app.wallet.hd import derive_pool_address, derive_user_address
+
+
+async def own_address_for(session: AsyncSession, kind: str, user_id: int | None) -> str:
+    """The address that owns every input of a PendingTransaction of this kind —
+    a user's own address for a bet/withdrawal, the pool address for a payout.
+    All our builders only ever spend one address's UTXOs per tx (see
+    tx/broadcast.py:_signing_context, which derives the same address alongside
+    the signing key it also needs).
+
+    Shared by tx/confirmation.py and tx/reconcile.py (B-41): both now check
+    blockchain.scripthash.get_history for this address instead of asking
+    blockchain.transaction.get for a verbose reply, so the two can't derive
+    different addresses for the same row.
+    """
+    if kind == "payout":
+        return derive_pool_address()
+    user = await session.get(User, user_id)
+    return derive_user_address(user.derivation_index)

app/tx/reconcile.py

@@ -36,7 +36,9 @@ from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker
 from app.audit.log import write_audit_log
 from app.db.models import PendingTransaction, Round, RoundParticipant, UtxoEvent, Withdrawal
 from app.electrum.client import ElectrumClient
+from app.electrum.scripthash import address_to_scripthash
 from app.rounds.events import broadcaster
+from app.tx.pending_address import own_address_for
 from app.wallet.balance import recompute_balance
 
 logger = logging.getLogger(__name__)
@@ -72,22 +74,21 @@ class PendingTransactionReconciler:
             await asyncio.sleep(_POLL_INTERVAL_SECONDS)
 
 
-async def _tx_exists_on_chain(client: ElectrumClient, txid: str) -> bool:
-    """True if the server knows this txid at all (mempool or mined). An error reply
-    means "unknown", which is the answer we're looking for; a transport failure is
-    *not* — that raises, and the caller leaves the row alone until next time."""
-    try:
-        tx = await client.get_transaction(txid, verbose=True)
-    except Exception as exc:
-        message = str(exc).lower()
-        if "missing" in message or "not found" in message or "no such" in message or "unknown" in message:
-            return False
-        raise
-    return bool(tx)
-
-
 async def reconcile_once(session_factory: async_sessionmaker, client: ElectrumClient) -> int:
-    """Returns how many rows were resolved (promoted or abandoned)."""
+    """Returns how many rows were resolved (promoted or abandoned).
+
+    Existence is decided by checking whether a row's own address's history
+    (blockchain.scripthash.get_history) includes its txid at all — mempool or
+    mined — rather than asking blockchain.transaction.get for a verbose reply
+    (B-41): several Electrum server implementations and versions reject the
+    verbose flag outright, and the previous substring-matching on the error
+    text (looking for "missing", "not found", ...) was fragile as the basis for
+    a decision that releases funds. A transport failure fetching history still
+    raises and leaves the row alone until next time — get_history not
+    returning our txid is the only thing that means "gone". History is cached
+    per scripthash within one pass, since every "payout" row shares the same
+    pool address.
+    """
     now = datetime.now(timezone.utc)
     async with session_factory() as session:
         rows = (
@@ -95,16 +96,25 @@ async def reconcile_once(session_factory: async_sessionmaker, client: ElectrumCl
                 select(PendingTransaction).where(PendingTransaction.status.in_(("building", "pending")))
             )
         ).all()
-        candidates = [
-            (row.id, row.status, row.current_txid)
-            for row in rows
-            if _is_due(row, now)
-        ]
+        candidates = []
+        for row in rows:
+            if not _is_due(row, now):
+                continue
+            try:
+                address = await own_address_for(session, row.kind, row.user_id)
+                scripthash = address_to_scripthash(address)
+            except Exception:
+                logger.exception("could not derive the address for pending_transaction %s", row.id)
+                continue
+            candidates.append((row.id, row.status, row.current_txid, scripthash))
 
     resolved = 0
-    for row_id, status, txid in candidates:
+    history_cache: dict[str, list[dict]] = {}
+    for row_id, status, txid, scripthash in candidates:
         try:
-            exists = await _tx_exists_on_chain(client, txid)
+            if scripthash not in history_cache:
+                history_cache[scripthash] = await client.get_history(scripthash)
+            exists = any(entry.get("tx_hash") == txid for entry in history_cache[scripthash])
         except Exception:
             # Transport/server problem — say nothing about this tx and try again on
             # the next pass rather than abandoning a tx that may be perfectly alive.

tests/unit/test_confirmation.py

@@ -1,41 +1,83 @@
 import pytest
-from sqlalchemy import select
 from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
 
 import app.bets.confirmation  # noqa: F401  (registers the "bet" handler)
 import app.rounds.confirmation  # noqa: F401  (registers the "payout" handler)
+from sqlalchemy import select
+
+from app.config import settings
 from app.db.base import Base
-from app.db.models import PendingTransaction, Round, RoundParticipant
+from app.db.models import PendingTransaction, Round, RoundParticipant, User
+from app.electrum.scripthash import address_to_scripthash
 from app.tx.confirmation import poll_once
+from app.wallet.hd import derive_user_address
 
 
 class FakeClient:
-    def __init__(self, confirmations_by_txid: dict[str, int]):
-        self._confirmations = confirmations_by_txid
+    """B-41: poll_once now asks blockchain.scripthash.get_history rather than a
+    verbose blockchain.transaction.get, so this hands back a flat history —
+    height > 0 means confirmed at that height, 0 (or absent) means still in the
+    mempool. The scripthash argument is ignored: every candidate's derived
+    address is looked up against the same known universe of txids, which is
+    fine since matching happens on tx_hash, not on which address asked."""
 
-    async def get_transaction(self, txid: str, verbose: bool = False) -> dict:
-        return {"confirmations": self._confirmations.get(txid, 0)}
+    def __init__(self, heights_by_txid: dict[str, int]):
+        self._heights = heights_by_txid
+
+    async def get_history(self, scripthash: str) -> list[dict]:
+        return [{"tx_hash": txid, "height": height} for txid, height in self._heights.items()]
 
 
 @pytest.fixture
-async def session_factory():
+async def session_factory(tmp_path, monkeypatch):
+    # own_address_for (B-41) derives each row's address via the HD wallet, so
+    # poll_once now needs a real master key — same bootstrap test_broadcast.py
+    # and test_reconcile.py use.
+    monkeypatch.setattr(settings, "master_key_path", str(tmp_path / "master.xprv.enc"))
+    monkeypatch.setattr(
+        settings,
+        "xprv_encryption_key",
+        __import__("cryptography.fernet", fromlist=["Fernet"]).Fernet.generate_key().decode(),
+    )
+    from app.wallet import hd
+
+    hd._account_key = None
+    hd.generate_master_key()
+
     engine = create_async_engine("sqlite+aiosqlite:///:memory:")
     async with engine.begin() as conn:
         await conn.run_sync(Base.metadata.create_all)
     yield async_sessionmaker(engine, expire_on_commit=False)
     await engine.dispose()
+    hd._account_key = None
+
+
+async def _make_user(session, derivation_index: int) -> User:
+    user = User(
+        username=f"user{derivation_index}",
+        password_hash="x",
+        derivation_index=derivation_index,
+        address=derive_user_address(derivation_index),
+    )
+    session.add(user)
+    await session.flush()
+    return user
 
 
 async def test_bet_confirmation_marks_participant_confirmed(session_factory):
     async with session_factory() as session:
+        user = await _make_user(session, 0)
         session.add(Round(id=1, status="open"))
         session.add(
             RoundParticipant(
-                round_id=1, user_id=1, bet_amount_sats=1_000, bet_txid="tx1", status="broadcast"
+                round_id=1, user_id=user.id, bet_amount_sats=1_000, bet_txid="tx1", status="broadcast"
             )
         )
         session.add(
-            PendingTransaction(kind="bet", round_id=1, user_id=1, current_txid="tx1", fee_rate_sat_vb=1, raw_tx_hex="00", status="pending")
+            PendingTransaction(
+                kind="bet", round_id=1, user_id=user.id, current_txid="tx1", fee_rate_sat_vb=1,
+                raw_tx_hex="00", status="pending",
+            )
         )
         await session.commit()
 
@@ -53,9 +95,17 @@ async def test_bet_confirmation_marks_participant_confirmed(session_factory):
 
 async def test_unconfirmed_tx_is_left_pending(session_factory):
     async with session_factory() as session:
+        user = await _make_user(session, 0)
         session.add(Round(id=2, status="open"))
-        session.add(RoundParticipant(round_id=2, user_id=1, bet_amount_sats=1_000, bet_txid="tx2", status="broadcast"))
-        session.add(PendingTransaction(kind="bet", round_id=2, user_id=1, current_txid="tx2", fee_rate_sat_vb=1, raw_tx_hex="00", status="pending"))
+        session.add(
+            RoundParticipant(round_id=2, user_id=user.id, bet_amount_sats=1_000, bet_txid="tx2", status="broadcast")
+        )
+        session.add(
+            PendingTransaction(
+                kind="bet", round_id=2, user_id=user.id, current_txid="tx2", fee_rate_sat_vb=1,
+                raw_tx_hex="00", status="pending",
+            )
+        )
         await session.commit()
 
     client = FakeClient({"tx2": 0})
@@ -70,7 +120,11 @@ async def test_unconfirmed_tx_is_left_pending(session_factory):
 async def test_payout_confirmation_closes_round(session_factory):
     async with session_factory() as session:
         session.add(Round(id=3, status="paying_out", payout_txid="tx3"))
-        session.add(PendingTransaction(kind="payout", round_id=3, current_txid="tx3", fee_rate_sat_vb=1, raw_tx_hex="00", status="pending"))
+        session.add(
+            PendingTransaction(
+                kind="payout", round_id=3, current_txid="tx3", fee_rate_sat_vb=1, raw_tx_hex="00", status="pending"
+            )
+        )
         await session.commit()
 
     client = FakeClient({"tx3": 2})
@@ -83,43 +137,52 @@ async def test_payout_confirmation_closes_round(session_factory):
 
 
 class ExplodingClient:
-    """Answers for one txid and raises for the other — a tx the server no longer
-    knows (dropped from the mempool, replaced by a bump)."""
+    """Answers for one address's history and raises for the other's — the
+    get_history equivalent of a server that no longer knows a particular tx
+    (dropped from the mempool, replaced by a bump)."""
 
-    def __init__(self, known: dict[str, int], exploding_txid: str):
-        self._known = known
-        self._exploding = exploding_txid
+    def __init__(self, heights_by_txid: dict[str, int], exploding_scripthash: str):
+        self._heights = heights_by_txid
+        self._exploding = exploding_scripthash
 
-    async def get_transaction(self, txid: str, verbose: bool = False) -> dict:
-        if txid == self._exploding:
-            raise RuntimeError("missing transaction")
-        return {"confirmations": self._known.get(txid, 0)}
+    async def get_history(self, scripthash: str) -> list[dict]:
+        if scripthash == self._exploding:
+            raise RuntimeError("server error")
+        return [{"tx_hash": txid, "height": height} for txid, height in self._heights.items()]
 
 
-async def test_one_unresolvable_txid_does_not_block_the_others(session_factory):
-    """B-03: the lookup used to be unguarded, so a single unknown txid aborted the
-    whole pass — nothing confirmed again until an operator intervened, which in turn
-    meant no round could ever close."""
+async def test_one_unresolvable_candidate_does_not_block_the_others(session_factory):
+    """B-03: the lookup used to be unguarded, so a single failing candidate aborted
+    the whole pass — nothing confirmed again until an operator intervened, which in
+    turn meant no round could ever close. B-41 changed the failure unit from "one
+    txid" to "one address's history", but the isolation guarantee is the same."""
     async with session_factory() as session:
+        good_user = await _make_user(session, 0)
+        gone_user = await _make_user(session, 1)
         session.add(Round(id=10, status="open"))
         session.add(
-            RoundParticipant(round_id=10, user_id=1, bet_amount_sats=1_000, bet_txid="good", status="broadcast")
-        )
-        session.add(
-            PendingTransaction(
-                kind="bet", round_id=10, user_id=2, current_txid="gone", fee_rate_sat_vb=1, raw_tx_hex="00",
-                status="pending",
+            RoundParticipant(
+                round_id=10, user_id=good_user.id, bet_amount_sats=1_000, bet_txid="good", status="broadcast"
             )
         )
         session.add(
             PendingTransaction(
-                kind="bet", round_id=10, user_id=1, current_txid="good", fee_rate_sat_vb=1, raw_tx_hex="00",
-                status="pending",
+                kind="bet", round_id=10, user_id=gone_user.id, current_txid="gone", fee_rate_sat_vb=1,
+                raw_tx_hex="00", status="pending",
+            )
+        )
+        session.add(
+            PendingTransaction(
+                kind="bet", round_id=10, user_id=good_user.id, current_txid="good", fee_rate_sat_vb=1,
+                raw_tx_hex="00", status="pending",
             )
         )
         await session.commit()
 
-    confirmed = await poll_once(session_factory, ExplodingClient({"good": 1}, exploding_txid="gone"))
+    exploding_scripthash = address_to_scripthash(derive_user_address(1))
+    confirmed = await poll_once(
+        session_factory, ExplodingClient({"good": 1}, exploding_scripthash=exploding_scripthash)
+    )
     assert confirmed == 1  # the healthy one still got processed
 
     async with session_factory() as session:
@@ -135,15 +198,16 @@ async def test_bet_confirms_after_an_rbf_bump_changed_the_txid(session_factory):
     a txid no participant carried — the participant stayed "broadcast" forever and
     the round could never close. It now resolves by (round_id, user_id)."""
     async with session_factory() as session:
+        user = await _make_user(session, 0)
         session.add(Round(id=11, status="open"))
         session.add(
             RoundParticipant(
-                round_id=11, user_id=7, bet_amount_sats=1_000, bet_txid="old-txid", status="broadcast"
+                round_id=11, user_id=user.id, bet_amount_sats=1_000, bet_txid="old-txid", status="broadcast"
             )
         )
         session.add(
             PendingTransaction(
-                kind="bet", round_id=11, user_id=7, current_txid="bumped-txid", fee_rate_sat_vb=2,
+                kind="bet", round_id=11, user_id=user.id, current_txid="bumped-txid", fee_rate_sat_vb=2,
                 raw_tx_hex="00", status="pending", replaced_by_txid="old-txid",
             )
         )
@@ -171,3 +235,35 @@ async def test_payout_confirms_after_an_rbf_bump_changed_the_txid(session_factor
 
     async with session_factory() as session:
         assert (await session.get(Round, 12)).status == "closed"
+
+
+async def test_poll_once_caches_history_per_scripthash(session_factory):
+    """Two pending bets from the same user share one address — fetching its
+    history twice in one pass would be wasteful."""
+    async with session_factory() as session:
+        user = await _make_user(session, 0)
+        session.add(Round(id=20, status="open"))
+        session.add(
+            PendingTransaction(
+                kind="bet", round_id=20, user_id=user.id, current_txid="tx-a", fee_rate_sat_vb=1,
+                raw_tx_hex="00", status="pending",
+            )
+        )
+        session.add(
+            PendingTransaction(
+                kind="withdrawal", user_id=user.id, current_txid="tx-b", fee_rate_sat_vb=1,
+                raw_tx_hex="00", status="pending",
+            )
+        )
+        await session.commit()
+
+    call_count = {"n": 0}
+
+    class CountingClient:
+        async def get_history(self, scripthash: str) -> list[dict]:
+            call_count["n"] += 1
+            return [{"tx_hash": "tx-a", "height": 0}, {"tx_hash": "tx-b", "height": 0}]
+
+    await poll_once(session_factory, CountingClient())
+
+    assert call_count["n"] == 1

tests/unit/test_pending_address.py

@@ -0,0 +1,55 @@
+"""B-41: own_address_for is the single place tx/confirmation.py and
+tx/reconcile.py derive a PendingTransaction's own address from — a payout's
+address must always be the pool's, everything else the actual user's."""
+
+import pytest
+from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
+
+from app.config import settings
+from app.db.base import Base
+from app.db.models import User
+from app.tx.pending_address import own_address_for
+
+
+@pytest.fixture
+async def session_factory(tmp_path, monkeypatch):
+    monkeypatch.setattr(settings, "master_key_path", str(tmp_path / "master.xprv.enc"))
+    monkeypatch.setattr(
+        settings,
+        "xprv_encryption_key",
+        __import__("cryptography.fernet", fromlist=["Fernet"]).Fernet.generate_key().decode(),
+    )
+    from app.wallet import hd
+
+    hd._account_key = None
+    hd.generate_master_key()
+
+    engine = create_async_engine("sqlite+aiosqlite:///:memory:")
+    async with engine.begin() as conn:
+        await conn.run_sync(Base.metadata.create_all)
+    yield async_sessionmaker(engine, expire_on_commit=False)
+    await engine.dispose()
+    hd._account_key = None
+
+
+async def test_payout_uses_the_pool_address_regardless_of_user_id(session_factory):
+    from app.wallet.hd import derive_pool_address
+
+    async with session_factory() as session:
+        address = await own_address_for(session, "payout", None)
+
+    assert address == derive_pool_address()
+
+
+@pytest.mark.parametrize("kind", ["bet", "withdrawal"])
+async def test_bet_and_withdrawal_use_the_users_own_address(session_factory, kind):
+    from app.wallet.hd import derive_user_address
+
+    async with session_factory() as session:
+        user = User(username="alice", password_hash="x", derivation_index=3, address=derive_user_address(3))
+        session.add(user)
+        await session.flush()
+
+        address = await own_address_for(session, kind, user.id)
+
+    assert address == derive_user_address(3)

tests/unit/test_reconcile.py

@@ -1,5 +1,10 @@
 """Regression tests for B-04 (and the "building" half of B-08): a transaction that
-never made it onto the chain must give the coins back instead of freezing them."""
+never made it onto the chain must give the coins back instead of freezing them.
+
+Also covers B-41: existence/reconciliation checks go through
+blockchain.scripthash.get_history rather than a verbose blockchain.transaction.get
+reply, so the fake clients below implement get_history.
+"""
 
 import pytest
 from embit import script
@@ -7,37 +12,60 @@ from embit.transaction import Transaction, TransactionInput, TransactionOutput
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import async_sessionmaker, create_async_engine
 
+from app.config import settings
 from app.db.base import Base
 from app.db.models import AuditLog, PendingTransaction, RoundParticipant, User, UtxoEvent, Withdrawal
 from app.tx.reconcile import reconcile_once
 
 
 class UnknownTxClient:
-    """A server that doesn't know any of the txids it's asked about."""
+    """A server whose history for any address never includes our txid."""
 
-    async def get_transaction(self, txid: str, verbose: bool = False):
-        raise RuntimeError(f"missing transaction {txid}")
+    async def get_history(self, scripthash: str) -> list[dict]:
+        return []
 
 
 class KnownTxClient:
-    async def get_transaction(self, txid: str, verbose: bool = False):
-        return {"txid": txid, "confirmations": 0}
+    """A server whose history for the address includes our txid — mined or
+    still in the mempool doesn't matter for existence, only for confirmation
+    (which is tx/confirmation.py's concern, not reconcile.py's)."""
+
+    def __init__(self, txid: str = "betxid"):
+        self._txid = txid
+
+    async def get_history(self, scripthash: str) -> list[dict]:
+        return [{"tx_hash": self._txid, "height": 100}]
 
 
 class BrokenClient:
     """A transport failure — says nothing about whether the tx exists."""
 
-    async def get_transaction(self, txid: str, verbose: bool = False):
+    async def get_history(self, scripthash: str) -> list[dict]:
         raise ConnectionResetError("connection reset")
 
 
 @pytest.fixture
-async def session_factory():
+async def session_factory(tmp_path, monkeypatch):
+    # own_address_for (B-41) derives each row's address via the HD wallet rather
+    # than trusting the DB's address column, so reconcile_once now needs a real
+    # master key set up — same bootstrap test_broadcast.py uses.
+    monkeypatch.setattr(settings, "master_key_path", str(tmp_path / "master.xprv.enc"))
+    monkeypatch.setattr(
+        settings,
+        "xprv_encryption_key",
+        __import__("cryptography.fernet", fromlist=["Fernet"]).Fernet.generate_key().decode(),
+    )
+    from app.wallet import hd
+
+    hd._account_key = None
+    hd.generate_master_key()
+
     engine = create_async_engine("sqlite+aiosqlite:///:memory:")
     async with engine.begin() as conn:
         await conn.run_sync(Base.metadata.create_all)
     yield async_sessionmaker(engine, expire_on_commit=False)
     await engine.dispose()
+    hd._account_key = None
 
 
 # A real (unsigned) transaction spending one input, built rather than hand-written
@@ -66,11 +94,19 @@ async def _seed_bet(
     participant_status: str,
     age_seconds: int,
     last_broadcast_age_seconds: int | None = None,
+    derivation_index: int = 0,
 ):
     from datetime import datetime, timedelta, timezone
 
+    from app.wallet.hd import derive_user_address
+
     async with session_factory() as session:
-        user = User(username="u", password_hash="x", derivation_index=0, address="plm1qtest")
+        user = User(
+            username="u",
+            password_hash="x",
+            derivation_index=derivation_index,
+            address=derive_user_address(derivation_index),
+        )
         session.add(user)
         await session.flush()
         session.add(
@@ -145,7 +181,7 @@ async def test_promotes_a_building_row_whose_tx_did_reach_the_chain(session_fact
         session_factory, pending_status="building", participant_status="building", age_seconds=300
     )
 
-    resolved = await reconcile_once(session_factory, KnownTxClient())
+    resolved = await reconcile_once(session_factory, KnownTxClient("betxid"))
     assert resolved == 1
 
     async with session_factory() as session:
@@ -219,8 +255,10 @@ async def test_abandoned_withdrawal_is_marked_failed_and_kept(session_factory):
     they can see it didn't go through."""
     from datetime import datetime, timedelta, timezone
 
+    from app.wallet.hd import derive_user_address
+
     async with session_factory() as session:
-        user = User(username="w", password_hash="x", derivation_index=1, address="plm1qtest2")
+        user = User(username="w", password_hash="x", derivation_index=1, address=derive_user_address(1))
         session.add(user)
         await session.flush()
         session.add(
@@ -264,3 +302,42 @@ async def test_abandoned_withdrawal_is_marked_failed_and_kept(session_factory):
         assert withdrawal.status == "failed"
         assert withdrawal.txid is None
         assert (await session.scalars(select(UtxoEvent))).one().spent_txid is None
+
+
+# --- B-41: existence checks now use get_history and share it across candidates
+# sharing the same address, instead of a per-tx verbose blockchain.transaction.get. --
+
+
+async def test_reconcile_once_caches_history_per_scripthash(session_factory):
+    """Two payout PendingTransaction rows always share the same pool address —
+    fetching its history twice in one pass would be wasteful and, at scale
+    across many candidates on one address, needlessly slow the whole tick."""
+    from datetime import datetime, timedelta, timezone
+
+    async with session_factory() as session:
+        old = datetime.now(timezone.utc) - timedelta(hours=7)
+        session.add(
+            PendingTransaction(
+                kind="payout", round_id=1, current_txid="payout-a", fee_rate_sat_vb=1,
+                raw_tx_hex=_RAW_TX, status="pending", broadcast_at=old, last_broadcast_at=old,
+            )
+        )
+        session.add(
+            PendingTransaction(
+                kind="payout", round_id=2, current_txid="payout-b", fee_rate_sat_vb=1,
+                raw_tx_hex=_RAW_TX, status="pending", broadcast_at=old, last_broadcast_at=old,
+            )
+        )
+        await session.commit()
+
+    call_count = {"n": 0}
+
+    class CountingClient:
+        async def get_history(self, scripthash: str) -> list[dict]:
+            call_count["n"] += 1
+            return [{"tx_hash": "payout-a", "height": 100}, {"tx_hash": "payout-b", "height": 100}]
+
+    resolved = await reconcile_once(session_factory, CountingClient())
+
+    assert resolved == 0  # both exist — nothing to abandon or promote (already "pending")
+    assert call_count["n"] == 1  # one call covered both rows sharing the pool address