FA-3731 / Binary formats / Open access

Delta encoding subtracts the initial sample every time · case 01

Delta encoding subtracts the initial sample every time.

Verified by executionVariant 1 · 4 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The implementation applies an operation whose text or grammar semantics violate this contract: Encode first integer unchanged and each later value minus its immediate predecessor.

VERIFIED REPAIR

Implement the complete stated contract, including the boundary fixtures: Encode first integer unchanged and each later value minus its immediate predecessor.

Unsuccessful approach: The attempted repair handles the primary example but still violates a separate boundary of the same contract.

Case contract

Encode first integer unchanged and each later value minus its immediate predecessor.

Why this case matters

A local executable model for consumers of structured text; oracle values are authored literals, not outputs copied from the repaired implementation.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return x
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve([10, 12, 15]), [10, 2, 3])
check('boundary 2', solve([2, 2, 2]), [2, 0, 0])
check('boundary 3', solve([]), [])
check('boundary 4', solve([5]), [5])
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 fixture	Actual	Expected	Outcome
boundary 1	`[10, 12, 15]`	`[10, 2, 3]`	Failed
boundary 2	`[2, 2, 2]`	`[2, 0, 0]`	Failed
boundary 3	`[]`	`[]`	Passed
boundary 4	`[5]`	`[5]`	Passed

SHA-256 / 8996c47a85055d750834a8ef1521bea59cc2c6c908359014d3fe10856635b825

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return [x[0]]+[v-x[0] for v in x[1:]] if x else []
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve([10, 12, 15]), [10, 2, 3])
check('boundary 2', solve([2, 2, 2]), [2, 0, 0])
check('boundary 3', solve([]), [])
check('boundary 4', solve([5]), [5])
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 fixture	Actual	Expected	Outcome
boundary 1	`[10, 2, 5]`	`[10, 2, 3]`	Failed
boundary 2	`[2, 0, 0]`	`[2, 0, 0]`	Passed
boundary 3	`[]`	`[]`	Passed
boundary 4	`[5]`	`[5]`	Passed

SHA-256 / 8befea8549d917a3ffc313e72de20372dfca0ba94864942ee23872e30da9a7e7

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return [x[0]]+[x[i]-x[i-1] for i in range(1,len(x))] if x else []
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve([10, 12, 15]), [10, 2, 3])
check('boundary 2', solve([2, 2, 2]), [2, 0, 0])
check('boundary 3', solve([]), [])
check('boundary 4', solve([5]), [5])
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 fixture	Actual	Expected	Outcome
boundary 1	`[10, 2, 3]`	`[10, 2, 3]`	Passed
boundary 2	`[2, 0, 0]`	`[2, 0, 0]`	Passed
boundary 3	`[]`	`[]`	Passed
boundary 4	`[5]`	`[5]`	Passed

SHA-256 / 357c05259cc7240c3e16878d64f57e5c053a119a1dedb5ebb1385a12f7676b4f

Verification & scope

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 2026-09-29T14:37:30.111275+00:00.

Case digest / e63c8f6651f6a6b521c7d2b00cb65b29ce3e886e3e33c1b6c8add8ddb5ceeaed