feat(v2): record fee_mismatch_sats per settlement, Phase 1 (#38 4/5)

Phase-1 observability per coord-log §2026-06-01T07:00Z (option A
locked: always record, no enforce_fee_match gate):

  fee_mismatch_sats = bitspire_fee_sats - (platform_fee_sats + operator_fee_sats)

Positive = bitspire over-reported; negative = under-reported; zero =
exact match. Recorded unconditionally on every settlement; WARN-
logged via loguru only when |delta| > tolerance, where
tolerance = max(1, int(principal_sats * 0.001)) — 1-sat floor with
0.1% relative ceiling.

bitspire.py:parse_settlement:
- Computes the delta after split_principal_based returns.
- WARN log line carries bitspire_fee_sats / expected / delta /
  tolerance / principal / both fractions / tx_type / machine-npub
  prefix for triage queries.
- Always stamps fee_mismatch_sats onto CreateDcaSettlementData.
- Comment explains the pre-Layer-3 expectation: large deltas are
  expected while the ATM hardcodes 7.77% cash-out (aiolabs/lamassu-
  next#57); the data here will quiet once Layer 3 ships.

crud.py:create_settlement_idempotent: extends the INSERT to persist
the new column.

Tests:
- tests/conftest.py: `loguru_capture` fixture — loguru routes to a
  pre-bound stderr sink that pytest's caplog (stdlib only) misses and
  capsys can't see; the fixture adds a list-sink for the test's
  duration. Reusable for future log-behavior tests.
- tests/test_fee_mismatch_recording.py: 8 cases covering exact-match
  zero delta, bitspire over- and under-reporting, the pre-Layer-3
  large-delta scenario, within-tolerance silence, over-tolerance
  warning, diagnostic-fields presence in the WARN line, and the
  1-sat floor on tiny-principal settlements.

164/164 tests green. Phase 2 (reject on out-of-tolerance) lands as
a follow-up once observability data justifies the tighter posture.

Refs: aiolabs/satmachineadmin#38 (Layer 1), coord-log §2026-06-01T07:00Z
(lnbits advisory + option A lock).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

bitspire.py

@@ -17,6 +17,8 @@ from __future__ import annotations
 import json
 from typing import Any, Optional
 
+from loguru import logger
+
 from .calculations import split_principal_based
 from .models import CreateDcaSettlementData, Machine, SuperConfig
 
@@ -275,6 +277,25 @@ def parse_settlement(
     platform_fee_sats, operator_fee_sats = split_principal_based(
         principal_sats, super_frac, operator_frac
     )
+    # Phase-1 observability per aiolabs/satmachineadmin#38 + coord-log
+    # §2026-06-01T07:00Z (option A locked): compare bitspire's reported
+    # fee_sats against satmachineadmin's recompute, log on out-of-
+    # tolerance drift, record the delta unconditionally for triage.
+    # Phase 2 (settlement-reject) lands after observability data.
+    fee_mismatch_sats = fee_sats - (platform_fee_sats + operator_fee_sats)
+    tolerance = max(1, int(principal_sats * 0.001))
+    if abs(fee_mismatch_sats) > tolerance:
+        logger.warning(
+            f"bitspire fee mismatch on payment {payment_hash[:12]}...: "
+            f"bitspire_fee_sats={fee_sats} expected={platform_fee_sats + operator_fee_sats} "
+            f"delta={fee_mismatch_sats} tolerance={tolerance} "
+            f"principal={principal_sats} super_frac={super_frac:.4f} "
+            f"operator_frac={operator_frac:.4f} tx_type={tx_type} "
+            f"machine={machine.machine_npub[:12]}... — "
+            "Phase 1 observability only, no behavior change. Pre-Layer-3 "
+            "(lamassu-next#57) the ATM still hardcodes fee fractions, so "
+            "large deltas here are expected until that ships."
+        )
     exchange_rate = _coerce_float(extra.get("exchange_rate"))
     if exchange_rate is None or exchange_rate <= 0:
         # Without exchange rate we can't compute fiat. Use 1.0 as a stand-in
@@ -301,6 +322,7 @@ def parse_settlement(
         fee_sats=fee_sats,
         platform_fee_sats=platform_fee_sats,
         operator_fee_sats=operator_fee_sats,
+        fee_mismatch_sats=fee_mismatch_sats,
         tx_type=tx_type,
         bills_json=_json_dumps(extra.get("bills")),
         cassettes_json=_json_dumps(extra.get("cassettes")),