FA-8901 / Selection controls / Open access

Two-thumb range-slider constraints: Dragging the selected range moves it outside the domain · case 01

Dragging the selected range moves it outside the domain.

Verified by executionVariant 1 · 9 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The translate operation uses `value` where the contract requires `max(minimum-low, min(value, maximum-high))`.

THE FAILURE

The translate operation uses `value` where the contract requires `max(minimum-low, min(value, maximum-high))`.

Unsuccessful approach: Clamping the delta as an absolute value ignores both thumb positions.

Case contract

Thumbs clamp to domain and maintain minimum separation; translating preserves span and clamps delta against both domain edges.

Why this case matters

A deterministic model of two-thumb range-slider constraints; this isolates one interface invariant without requiring a browser.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(low, high, target, value, minimum, maximum, gap):
    if target == 'low': low = max(minimum, min(value, high-gap))
    elif target == 'high': high = min(maximum, max(value, low+gap))
    elif target == 'translate':
        delta = value
        low += delta; high += delta
    return (low, high)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('low minimum', solve(20, 60, 'low', -10, 0, 100, 10), (0, 60))
check('low gap', solve(20, 60, 'low', 65, 0, 100, 10), (50, 60))
check('high maximum', solve(20, 60, 'high', 120, 0, 100, 10), (20, 100))
check('high gap', solve(20, 60, 'high', 15, 0, 100, 10), (20, 30))
check('translate upper', solve(20, 60, 'translate', 80, 0, 100, 10), (60, 100))
check('translate lower', solve(20, 60, 'translate', -40, 0, 100, 10), (0, 40))
check('ordinary', solve(20, 60, 'low', 30, 0, 100, 10), (30, 60))
check('parameterized range translation', solve(2*N,6*N,'translate',N,0,10*N,N), (3*N,7*N))
for repetition in range(N):
    check('repeat ordinary', solve(20, 60, 'low', 30, 0, 100, 10), (30, 60))
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
low minimum	`[0, 60]`	`[0, 60]`	Passed
low gap	`[50, 60]`	`[50, 60]`	Passed
high maximum	`[20, 100]`	`[20, 100]`	Passed
high gap	`[20, 30]`	`[20, 30]`	Passed
translate upper	`[100, 140]`	`[60, 100]`	Failed
translate lower	`[-20, 20]`	`[0, 40]`	Failed
ordinary	`[30, 60]`	`[30, 60]`	Passed
parameterized range translation	`[3, 7]`	`[3, 7]`	Passed
repeat ordinary	`[30, 60]`	`[30, 60]`	Passed

SHA-256 / e9a10fb3648cddf421629e88e0be0e62e74bf077580b13fa5c5eb565a41dc17e

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(low, high, target, value, minimum, maximum, gap):
    if target == 'low': low = max(minimum, min(value, high-gap))
    elif target == 'high': high = min(maximum, max(value, low+gap))
    elif target == 'translate':
        delta = max(minimum, min(value, maximum))
        low += delta; high += delta
    return (low, high)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('low minimum', solve(20, 60, 'low', -10, 0, 100, 10), (0, 60))
check('low gap', solve(20, 60, 'low', 65, 0, 100, 10), (50, 60))
check('high maximum', solve(20, 60, 'high', 120, 0, 100, 10), (20, 100))
check('high gap', solve(20, 60, 'high', 15, 0, 100, 10), (20, 30))
check('translate upper', solve(20, 60, 'translate', 80, 0, 100, 10), (60, 100))
check('translate lower', solve(20, 60, 'translate', -40, 0, 100, 10), (0, 40))
check('ordinary', solve(20, 60, 'low', 30, 0, 100, 10), (30, 60))
check('parameterized range translation', solve(2*N,6*N,'translate',N,0,10*N,N), (3*N,7*N))
for repetition in range(N):
    check('repeat ordinary', solve(20, 60, 'low', 30, 0, 100, 10), (30, 60))
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
low minimum	`[0, 60]`	`[0, 60]`	Passed
low gap	`[50, 60]`	`[50, 60]`	Passed
high maximum	`[20, 100]`	`[20, 100]`	Passed
high gap	`[20, 30]`	`[20, 30]`	Passed
translate upper	`[100, 140]`	`[60, 100]`	Failed
translate lower	`[20, 60]`	`[0, 40]`	Failed
ordinary	`[30, 60]`	`[30, 60]`	Passed
parameterized range translation	`[3, 7]`	`[3, 7]`	Passed
repeat ordinary	`[30, 60]`	`[30, 60]`	Passed

SHA-256 / 2f2cbaa2b18ddde0a0488b6cf5411ab35eff1d0b886195ead60277695d320b89

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 9 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

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 2026-09-29T14:38:25.414951+00:00.

Case digest / e687ef1784bbdfd3c66fc797027a97879d1bbb272790b613249ba08b627e9e05