Give every round its own pool address (B-80, RND-35, DAT-60, DAT-11, REG-14, SEC-08, BET-12, RND-22, WDR-14, SEC-43, API-23, API-36)

All bets of all rounds paid one address (m/84'/746'/0'/1/0), so its history
grew forever, other rounds' money and stray coins mixed with a round's own, and
the payout picked from everything it held.

- hd.py: derive_pool_key/derive_pool_address(round_id) on branch 2
  (m/84'/746'/0'/2/<round_id>); no argument is the reserve address 1/0.
  derive_round_pool_key checks the key against the address stored on the round,
  so a payout can never be signed for money its key does not control.
- rounds.pool_address (migration 477bddae1a84, existing rounds backfilled with
  the reserve address since that is where their bets went; add_column, not a
  batch alter, so the expression indexes stay): written in the transaction that
  inserts the round, once its id exists.
- place_bet pays round.pool_address; the payout reads, signs and takes change at
  the round's own address; own_address_for and bump_fee's _signing_context follow
  the round (confirmation poller and reconciler pass round_id).
- Withdrawals to any round pool address, the reserve address or fee_address are
  refused (withdrawal_to_platform_address, 400, all seven languages).
- GET /rounds/current and GET /admin/rounds expose pool_address.
- RND-22/DAT-11 stay "da implementare" for B-82: the payout still spends every
  confirmed coin at the round's address, not only the participants' outpoints
  (participants carry no bet_vout yet).
- tests/unit/conftest.py: every test now gets a throwaway master key. Opening a
  round derives an address, and tests that merely opened a round were silently
  reading the real key from the local .env.
- Existing tests changed because the spec changed: payout fixtures give their
  round a pool_address; the reconciler's address-cache test uses two payouts of
  one round (rows of different rounds no longer share an address);
  own_address_for now takes the round id.

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

app/api/routes/admin.py

@@ -241,6 +241,7 @@ class AdminRoundResponse(BaseModel):
     winner_amount_sats: int | None
     fee_amount_sats: int | None
     payout_txid: str | None
+    pool_address: str | None  # B-80
 
 
 @router.get("/rounds", response_model=list[AdminRoundResponse], dependencies=[Depends(require_admin)])
@@ -268,6 +269,7 @@ async def list_rounds(
             winner_amount_sats=r.winner_amount_sats,
             fee_amount_sats=r.fee_amount_sats,
             payout_txid=r.payout_txid,
+            pool_address=r.pool_address or None,
         )
         for r in rounds
     ]

app/api/routes/rounds.py

@@ -89,6 +89,9 @@ class CurrentRoundResponse(BaseModel):
     server_time: str
     round_id: int | None = None
     status: str | None = None
+    # B-80 (RND-35): this round's own pool address, so anyone can verify its money on
+    # an explorer; null when there is no active round.
+    pool_address: str | None = None
     opened_at: str | None = None
     closes_at: str | None = None
     # B-65: confirmed participants only — the ones the draw actually picks from and
@@ -205,6 +208,7 @@ async def current_round(
         server_time=datetime.now(timezone.utc).isoformat(),
         round_id=round_.id,
         status=round_.status,
+        pool_address=round_.pool_address or None,
         opened_at=opened_at.isoformat(),
         closes_at=closes_at.isoformat(),
         participant_count=participant_count,