FA-8781 / Viewport layout / Open access

Split-pane divider allocation: Divider width is counted as usable pane area · case 01

Divider width is counted as usable pane area.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The divider operation uses `total` where the contract requires `max(0, total - divider)`.

VERIFIED REPAIR

Implement the divider operation as `max(0, total - divider)`.

Unsuccessful approach: Adding divider width expands children beyond their container.

Case contract

Subtract divider from total; honor both minimums when feasible; otherwise share available width in proportion to minima; panes sum to available space.

Why this case matters

A deterministic model of split-pane divider allocation; 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(total, divider, requested, minimum_first, minimum_second):
    available = total
    if available < minimum_first + minimum_second:
        first = available * minimum_first / (minimum_first + minimum_second) if minimum_first + minimum_second else 0
    else: first = max(minimum_first, min(requested, available-minimum_second))
    return (first, available-first)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('normal', solve(110, 10, 40, 20, 30), (40, 60))
check('narrow', solve(40, 10, 25, 20, 40), (10, 20))
check('first min', solve(110, 10, 5, 20, 30), (20, 80))
check('second min', solve(110, 10, 95, 20, 30), (70, 30))
check('large request', solve(210, 10, 100, 20, 40), (100, 100))
check('zero', solve(0, 10, 5, 0, 0), (0, 0))
check('parameterized panel extent', solve(11*N,N,4*N,2*N,3*N), (4*N,6*N))
for repetition in range(N):
    check('repeat zero', solve(0, 10, 5, 0, 0), (0, 0))
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
normal	`[40, 70]`	`[40, 60]`	Failed
narrow	`[13.333333333333334, 26.666666666666664]`	`[10, 20]`	Failed
first min	`[20, 90]`	`[20, 80]`	Failed
second min	`[80, 30]`	`[70, 30]`	Failed
large request	`[100, 110]`	`[100, 100]`	Failed
zero	`[0, 0]`	`[0, 0]`	Passed
parameterized panel extent	`[4, 7]`	`[4, 6]`	Failed
repeat zero	`[0, 0]`	`[0, 0]`	Passed

SHA-256 / d6095a90480087c7dbdb2fa277d1d8044b6d47e16d9142caac0f791af9ab6603

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(total, divider, requested, minimum_first, minimum_second):
    available = max(0, total + divider)
    if available < minimum_first + minimum_second:
        first = available * minimum_first / (minimum_first + minimum_second) if minimum_first + minimum_second else 0
    else: first = max(minimum_first, min(requested, available-minimum_second))
    return (first, available-first)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('normal', solve(110, 10, 40, 20, 30), (40, 60))
check('narrow', solve(40, 10, 25, 20, 40), (10, 20))
check('first min', solve(110, 10, 5, 20, 30), (20, 80))
check('second min', solve(110, 10, 95, 20, 30), (70, 30))
check('large request', solve(210, 10, 100, 20, 40), (100, 100))
check('zero', solve(0, 10, 5, 0, 0), (0, 0))
check('parameterized panel extent', solve(11*N,N,4*N,2*N,3*N), (4*N,6*N))
for repetition in range(N):
    check('repeat zero', solve(0, 10, 5, 0, 0), (0, 0))
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
normal	`[40, 80]`	`[40, 60]`	Failed
narrow	`[16.666666666666668, 33.33333333333333]`	`[10, 20]`	Failed
first min	`[20, 100]`	`[20, 80]`	Failed
second min	`[90, 30]`	`[70, 30]`	Failed
large request	`[100, 120]`	`[100, 100]`	Failed
zero	`[5, 5]`	`[0, 0]`	Failed
parameterized panel extent	`[4, 8]`	`[4, 6]`	Failed
repeat zero	`[5, 5]`	`[0, 0]`	Failed

SHA-256 / dbcf85e1fc7673247a1959568003e84e403a274a18ac64214c3c9c4f4fa7abfe

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(total, divider, requested, minimum_first, minimum_second):
    available = max(0, total - divider)
    if available < minimum_first + minimum_second:
        first = available * minimum_first / (minimum_first + minimum_second) if minimum_first + minimum_second else 0
    else: first = max(minimum_first, min(requested, available-minimum_second))
    return (first, available-first)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('normal', solve(110, 10, 40, 20, 30), (40, 60))
check('narrow', solve(40, 10, 25, 20, 40), (10, 20))
check('first min', solve(110, 10, 5, 20, 30), (20, 80))
check('second min', solve(110, 10, 95, 20, 30), (70, 30))
check('large request', solve(210, 10, 100, 20, 40), (100, 100))
check('zero', solve(0, 10, 5, 0, 0), (0, 0))
check('parameterized panel extent', solve(11*N,N,4*N,2*N,3*N), (4*N,6*N))
for repetition in range(N):
    check('repeat zero', solve(0, 10, 5, 0, 0), (0, 0))
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
normal	`[40, 60]`	`[40, 60]`	Passed
narrow	`[10.0, 20.0]`	`[10, 20]`	Passed
first min	`[20, 80]`	`[20, 80]`	Passed
second min	`[70, 30]`	`[70, 30]`	Passed
large request	`[100, 100]`	`[100, 100]`	Passed
zero	`[0, 0]`	`[0, 0]`	Passed
parameterized panel extent	`[4, 6]`	`[4, 6]`	Passed
repeat zero	`[0, 0]`	`[0, 0]`	Passed

SHA-256 / 84a7b04bb68409fee8bd671c515efd5153647a4cfe6b5f3eb5d0f204357f8801

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 2026-09-29T14:38:24.382636+00:00.

Case digest / a7e85158b3b5871251df63593d648162a99ea2ebf8c6acef5bbc566ed55ee6df