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FA-85821 / Ride-hailing fare and surge pricing / Open access

Reservation fee absorbed by the guarantee · case 01

Riders with a metered fare above booked pay no reservation fee.

Verified by executionVariant 1 · 7 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The fee is inside the min, so the guarantee swallows it.

VERIFIED REPAIR

Add the reservation fee after taking the lower fare.

Unsuccessful approach: Adding the fee to the booked side only drops it when the meter is lower.

Case contract

Scheduled rides guarantee the booked price: the rider pays the lower of booked and metered fare plus the reservation fee. If the driver never shows, nothing is charged and the reservation fee is refunded. Return charge cents and whether the fee is refunded.

Why this case matters

Ride-hailing prices are computed per trip at scale; ordering, unit and boundary slips become systematic over- or under-charging.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(booked_price, metered, driver_no_show, reservation_fee):
    if driver_no_show:
        return {'charge': 0, 'refund_fee': True}
    return {'charge': min(booked_price, metered + reservation_fee), 'refund_fee': False}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: reservation fee placement', [3200, 3200, False, 300], {'charge': 3500, 'refund_fee': False}),
  ('partial repair probe: reservation fee placement', [4100, 4100, False, 300],
   {'charge': 4400, 'refund_fee': False}),
  ('second regression', [3200, 3199, False, 200], {'charge': 3399, 'refund_fee': False}),
  ('normal control 1', [2500, 1800, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 2', [4100, 3400, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 3', [3200, 3201, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 4', [2500, 2501, True, 300], {'charge': 0, 'refund_fee': True})],
 [('regression: reservation fee placement', [3200, 3200, False, 200], {'charge': 3400, 'refund_fee': False}),
  ('partial repair probe: reservation fee placement', [2500, 2500, False, 300],
   {'charge': 2800, 'refund_fee': False}),
  ('second regression', [2500, 2500, False, 200], {'charge': 2700, 'refund_fee': False}),
  ('normal control 1', [2500, 2501, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 2', [3200, 4100, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 3', [3200, 4100, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 4', [2500, 2500, True, 300], {'charge': 0, 'refund_fee': True})],
 [('regression: reservation fee placement', [3200, 3199, False, 200], {'charge': 3399, 'refund_fee': False}),
  ('partial repair probe: reservation fee placement', [2500, 1800, False, 200],
   {'charge': 2000, 'refund_fee': False}),
  ('second regression', [2500, 2499, False, 300], {'charge': 2799, 'refund_fee': False}),
  ('normal control 1', [3200, 3200, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 2', [3200, 3201, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 3', [3200, 2500, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 4', [2500, 2500, True, 200], {'charge': 0, 'refund_fee': True})],
 [('regression: reservation fee placement', [4100, 4101, False, 300], {'charge': 4400, 'refund_fee': False}),
  ('partial repair probe: reservation fee placement', [3200, 3199, False, 200],
   {'charge': 3399, 'refund_fee': False}),
  ('second regression', [4100, 4101, False, 200], {'charge': 4300, 'refund_fee': False}),
  ('normal control 1', [2500, 2501, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 2', [2500, 2501, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 3', [3200, 3200, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 4', [3200, 3199, True, 300], {'charge': 0, 'refund_fee': True})],
 [('regression: reservation fee placement', [4100, 4099, False, 200], {'charge': 4299, 'refund_fee': False}),
  ('partial repair probe: reservation fee placement', [4100, 3400, False, 300],
   {'charge': 3700, 'refund_fee': False}),
  ('second regression', [4100, 4101, False, 300], {'charge': 4400, 'refund_fee': False}),
  ('normal control 1', [2500, 2500, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 2', [4100, 4099, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 3', [3200, 3201, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 4', [3200, 3199, True, 200], {'charge': 0, 'refund_fee': True})]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression: reservation fee placement{'charge': 3200, 'refund_fee': False}{'charge': 3500, 'refund_fee': False}Failed
partial repair probe: reservation fee placement{'charge': 4100, 'refund_fee': False}{'charge': 4400, 'refund_fee': False}Failed
second regression{'charge': 3200, 'refund_fee': False}{'charge': 3399, 'refund_fee': False}Failed
normal control 1{'charge': 0, 'refund_fee': True}{'charge': 0, 'refund_fee': True}Passed
normal control 2{'charge': 0, 'refund_fee': True}{'charge': 0, 'refund_fee': True}Passed
normal control 3{'charge': 0, 'refund_fee': True}{'charge': 0, 'refund_fee': True}Passed
normal control 4{'charge': 0, 'refund_fee': True}{'charge': 0, 'refund_fee': True}Passed

SHA-256 / d127af91b72e80a9ab539adf860f95b8b53a551da6d9b32be455622971e98489

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(booked_price, metered, driver_no_show, reservation_fee):
    if driver_no_show:
        return {'charge': 0, 'refund_fee': True}
    return {'charge': min(booked_price + reservation_fee, metered), 'refund_fee': False}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: reservation fee placement', [3200, 3200, False, 300], {'charge': 3500, 'refund_fee': False}),
  ('partial repair probe: reservation fee placement', [4100, 4100, False, 300],
   {'charge': 4400, 'refund_fee': False}),
  ('second regression', [3200, 3199, False, 200], {'charge': 3399, 'refund_fee': False}),
  ('normal control 1', [2500, 1800, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 2', [4100, 3400, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 3', [3200, 3201, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 4', [2500, 2501, True, 300], {'charge': 0, 'refund_fee': True})],
 [('regression: reservation fee placement', [3200, 3200, False, 200], {'charge': 3400, 'refund_fee': False}),
  ('partial repair probe: reservation fee placement', [2500, 2500, False, 300],
   {'charge': 2800, 'refund_fee': False}),
  ('second regression', [2500, 2500, False, 200], {'charge': 2700, 'refund_fee': False}),
  ('normal control 1', [2500, 2501, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 2', [3200, 4100, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 3', [3200, 4100, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 4', [2500, 2500, True, 300], {'charge': 0, 'refund_fee': True})],
 [('regression: reservation fee placement', [3200, 3199, False, 200], {'charge': 3399, 'refund_fee': False}),
  ('partial repair probe: reservation fee placement', [2500, 1800, False, 200],
   {'charge': 2000, 'refund_fee': False}),
  ('second regression', [2500, 2499, False, 300], {'charge': 2799, 'refund_fee': False}),
  ('normal control 1', [3200, 3200, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 2', [3200, 3201, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 3', [3200, 2500, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 4', [2500, 2500, True, 200], {'charge': 0, 'refund_fee': True})],
 [('regression: reservation fee placement', [4100, 4101, False, 300], {'charge': 4400, 'refund_fee': False}),
  ('partial repair probe: reservation fee placement', [3200, 3199, False, 200],
   {'charge': 3399, 'refund_fee': False}),
  ('second regression', [4100, 4101, False, 200], {'charge': 4300, 'refund_fee': False}),
  ('normal control 1', [2500, 2501, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 2', [2500, 2501, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 3', [3200, 3200, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 4', [3200, 3199, True, 300], {'charge': 0, 'refund_fee': True})],
 [('regression: reservation fee placement', [4100, 4099, False, 200], {'charge': 4299, 'refund_fee': False}),
  ('partial repair probe: reservation fee placement', [4100, 3400, False, 300],
   {'charge': 3700, 'refund_fee': False}),
  ('second regression', [4100, 4101, False, 300], {'charge': 4400, 'refund_fee': False}),
  ('normal control 1', [2500, 2500, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 2', [4100, 4099, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 3', [3200, 3201, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 4', [3200, 3199, True, 200], {'charge': 0, 'refund_fee': True})]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression: reservation fee placement{'charge': 3200, 'refund_fee': False}{'charge': 3500, 'refund_fee': False}Failed
partial repair probe: reservation fee placement{'charge': 4100, 'refund_fee': False}{'charge': 4400, 'refund_fee': False}Failed
second regression{'charge': 3199, 'refund_fee': False}{'charge': 3399, 'refund_fee': False}Failed
normal control 1{'charge': 0, 'refund_fee': True}{'charge': 0, 'refund_fee': True}Passed
normal control 2{'charge': 0, 'refund_fee': True}{'charge': 0, 'refund_fee': True}Passed
normal control 3{'charge': 0, 'refund_fee': True}{'charge': 0, 'refund_fee': True}Passed
normal control 4{'charge': 0, 'refund_fee': True}{'charge': 0, 'refund_fee': True}Passed

SHA-256 / 5115b7d995bd7f145eebb8679da8de692588738d874c96d87d4ca825721ed1a0

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(booked_price, metered, driver_no_show, reservation_fee):
    if driver_no_show:
        return {'charge': 0, 'refund_fee': True}
    return {'charge': min(booked_price, metered) + reservation_fee, 'refund_fee': False}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: reservation fee placement', [3200, 3200, False, 300], {'charge': 3500, 'refund_fee': False}),
  ('partial repair probe: reservation fee placement', [4100, 4100, False, 300],
   {'charge': 4400, 'refund_fee': False}),
  ('second regression', [3200, 3199, False, 200], {'charge': 3399, 'refund_fee': False}),
  ('normal control 1', [2500, 1800, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 2', [4100, 3400, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 3', [3200, 3201, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 4', [2500, 2501, True, 300], {'charge': 0, 'refund_fee': True})],
 [('regression: reservation fee placement', [3200, 3200, False, 200], {'charge': 3400, 'refund_fee': False}),
  ('partial repair probe: reservation fee placement', [2500, 2500, False, 300],
   {'charge': 2800, 'refund_fee': False}),
  ('second regression', [2500, 2500, False, 200], {'charge': 2700, 'refund_fee': False}),
  ('normal control 1', [2500, 2501, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 2', [3200, 4100, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 3', [3200, 4100, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 4', [2500, 2500, True, 300], {'charge': 0, 'refund_fee': True})],
 [('regression: reservation fee placement', [3200, 3199, False, 200], {'charge': 3399, 'refund_fee': False}),
  ('partial repair probe: reservation fee placement', [2500, 1800, False, 200],
   {'charge': 2000, 'refund_fee': False}),
  ('second regression', [2500, 2499, False, 300], {'charge': 2799, 'refund_fee': False}),
  ('normal control 1', [3200, 3200, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 2', [3200, 3201, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 3', [3200, 2500, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 4', [2500, 2500, True, 200], {'charge': 0, 'refund_fee': True})],
 [('regression: reservation fee placement', [4100, 4101, False, 300], {'charge': 4400, 'refund_fee': False}),
  ('partial repair probe: reservation fee placement', [3200, 3199, False, 200],
   {'charge': 3399, 'refund_fee': False}),
  ('second regression', [4100, 4101, False, 200], {'charge': 4300, 'refund_fee': False}),
  ('normal control 1', [2500, 2501, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 2', [2500, 2501, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 3', [3200, 3200, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 4', [3200, 3199, True, 300], {'charge': 0, 'refund_fee': True})],
 [('regression: reservation fee placement', [4100, 4099, False, 200], {'charge': 4299, 'refund_fee': False}),
  ('partial repair probe: reservation fee placement', [4100, 3400, False, 300],
   {'charge': 3700, 'refund_fee': False}),
  ('second regression', [4100, 4101, False, 300], {'charge': 4400, 'refund_fee': False}),
  ('normal control 1', [2500, 2500, True, 200], {'charge': 0, 'refund_fee': True}),
  ('normal control 2', [4100, 4099, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 3', [3200, 3201, True, 300], {'charge': 0, 'refund_fee': True}),
  ('normal control 4', [3200, 3199, True, 200], {'charge': 0, 'refund_fee': True})]]
for label, args, expected in fixtures[N-1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression: reservation fee placement{'charge': 3500, 'refund_fee': False}{'charge': 3500, 'refund_fee': False}Passed
partial repair probe: reservation fee placement{'charge': 4400, 'refund_fee': False}{'charge': 4400, 'refund_fee': False}Passed
second regression{'charge': 3399, 'refund_fee': False}{'charge': 3399, 'refund_fee': False}Passed
normal control 1{'charge': 0, 'refund_fee': True}{'charge': 0, 'refund_fee': True}Passed
normal control 2{'charge': 0, 'refund_fee': True}{'charge': 0, 'refund_fee': True}Passed
normal control 3{'charge': 0, 'refund_fee': True}{'charge': 0, 'refund_fee': True}Passed
normal control 4{'charge': 0, 'refund_fee': True}{'charge': 0, 'refund_fee': True}Passed

SHA-256 / 2e56bf6cfcff0facf2546b2ec66113d4258c53845799caf80ce53b44d6df0301

Verification & scope

A deterministic toy pricing contract stipulated for this example; it does not reproduce the pricing of any real ride-hailing operator or regulator. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:50:43.842334+00:00.

Case digest / 0bacd484f3401191ff2c1e9b0b18cec6d1aedb42110dcdb755f2829b6ffd9820