FA-54051 / Accessibility interaction semantics / Open access
A terminal child page advertises an extra empty page · case 01
A terminal child page advertises an extra empty page.
ROOT CAUSE
The terminal continuation decision in the child pages adapter violates its declared contract.
THE FAILURE
The terminal continuation decision in the child pages adapter violates its declared contract.
Unsuccessful approach: The local repair substitutes start+len(page) != len(items)-1 but still mishandles the regression fixtures.
Case contract
Input [children,start,count,revision,requested_revision,exposed_ids]. Page accessibility child descriptors in source order, first dedupe IDs then filter exposed IDs. start/count must be nonnegative integers excluding booleans; invalid returns {error:range}. Stale requested revision returns {error:stale} before range checks. Return children slice, total exposed unique count, next offset or None, revision. Zero count yields empty page with next None to avoid nonprogress. Start beyond total gives empty and next None.
Why this case matters
Offline accessibility bridge model with explicit policy; useful for testing semantic API adapters independently of browser implementations.
1 / The failure
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(data):
children,start,count,revision,requested,exposed = data
if requested != revision: return {'error':'stale'}
if type(start) is not int or type(count) is not int or start < 0 or count < 0: return {'error':'range'}
items = [x for x in dict.fromkeys(children) if x in exposed]
page = items[start:start+count]
nxt = start+len(page) if page and start+len(page) <= len(items) else None
return {'children':page,'total':len(items),'next':nxt,'revision':revision}
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('contract fixture 1', solve([['a','hidden','b','a','c'],0,2,N,N,['a','b','c']],), {'children':['a','b'],'total':3,'next':2,'revision':N})
check('contract fixture 2', solve([['a','b','c'],2,4,N,N,['a','b','c']],), {'children':['c'],'total':3,'next':None,'revision':N})
check('contract fixture 3', solve([['a','b'],0,0,N,N,['a','b']],), {'children':[],'total':2,'next':None,'revision':N})
check('contract fixture 4', solve([['a'],-1,2,N,N-1,['a']],), {'error':'stale'})
check('contract fixture 5', solve([['a'],True,1,N,N,['a']],), {'error':'range'})
check('contract fixture 6', solve([['a'],0,False,N,N,['a']],), {'error':'range'})
check('contract fixture 7', solve([['a'],0,-1,N,N,['a']],), {'error':'range'})
check('contract fixture 8', solve([['a'],-1,1,N,N,['a']],), {'error':'range'})
check('contract fixture 9', solve([['a','b','c'],1,1,N,N,['a','b','c']],), {'children':['b'],'total':3,'next':2,'revision':N})
check('contract fixture 10', solve([['a'],N+2,1,N,N,['a']],), {'children':[],'total':1,'next':None,'revision':N})
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 |
|---|---|---|---|
| contract fixture 1 | {'children': ['a', 'b'], 'next': 2, 'revision': 1, 'total': 3} | {'children': ['a', 'b'], 'next': 2, 'revision': 1, 'total': 3} | Passed |
| contract fixture 2 | {'children': ['c'], 'next': 3, 'revision': 1, 'total': 3} | {'children': ['c'], 'next': None, 'revision': 1, 'total': 3} | Failed |
| contract fixture 3 | {'children': [], 'next': None, 'revision': 1, 'total': 2} | {'children': [], 'next': None, 'revision': 1, 'total': 2} | Passed |
| contract fixture 4 | {'error': 'stale'} | {'error': 'stale'} | Passed |
| contract fixture 5 | {'error': 'range'} | {'error': 'range'} | Passed |
| contract fixture 6 | {'error': 'range'} | {'error': 'range'} | Passed |
| contract fixture 7 | {'error': 'range'} | {'error': 'range'} | Passed |
| contract fixture 8 | {'error': 'range'} | {'error': 'range'} | Passed |
| contract fixture 9 | {'children': ['b'], 'next': 2, 'revision': 1, 'total': 3} | {'children': ['b'], 'next': 2, 'revision': 1, 'total': 3} | Passed |
| contract fixture 10 | {'children': [], 'next': None, 'revision': 1, 'total': 1} | {'children': [], 'next': None, 'revision': 1, 'total': 1} | Passed |
SHA-256 / bdc8b641648af22fe0f82daab827283bd581a0d2773666e8ef0b6edacef6df00
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
N = 1
observations = []
def solve(data):
children,start,count,revision,requested,exposed = data
if requested != revision: return {'error':'stale'}
if type(start) is not int or type(count) is not int or start < 0 or count < 0: return {'error':'range'}
items = [x for x in dict.fromkeys(children) if x in exposed]
page = items[start:start+count]
nxt = start+len(page) if page and start+len(page) != len(items)-1 else None
return {'children':page,'total':len(items),'next':nxt,'revision':revision}
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('contract fixture 1', solve([['a','hidden','b','a','c'],0,2,N,N,['a','b','c']],), {'children':['a','b'],'total':3,'next':2,'revision':N})
check('contract fixture 2', solve([['a','b','c'],2,4,N,N,['a','b','c']],), {'children':['c'],'total':3,'next':None,'revision':N})
check('contract fixture 3', solve([['a','b'],0,0,N,N,['a','b']],), {'children':[],'total':2,'next':None,'revision':N})
check('contract fixture 4', solve([['a'],-1,2,N,N-1,['a']],), {'error':'stale'})
check('contract fixture 5', solve([['a'],True,1,N,N,['a']],), {'error':'range'})
check('contract fixture 6', solve([['a'],0,False,N,N,['a']],), {'error':'range'})
check('contract fixture 7', solve([['a'],0,-1,N,N,['a']],), {'error':'range'})
check('contract fixture 8', solve([['a'],-1,1,N,N,['a']],), {'error':'range'})
check('contract fixture 9', solve([['a','b','c'],1,1,N,N,['a','b','c']],), {'children':['b'],'total':3,'next':2,'revision':N})
check('contract fixture 10', solve([['a'],N+2,1,N,N,['a']],), {'children':[],'total':1,'next':None,'revision':N})
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 |
|---|---|---|---|
| contract fixture 1 | {'children': ['a', 'b'], 'next': None, 'revision': 1, 'total': 3} | {'children': ['a', 'b'], 'next': 2, 'revision': 1, 'total': 3} | Failed |
| contract fixture 2 | {'children': ['c'], 'next': 3, 'revision': 1, 'total': 3} | {'children': ['c'], 'next': None, 'revision': 1, 'total': 3} | Failed |
| contract fixture 3 | {'children': [], 'next': None, 'revision': 1, 'total': 2} | {'children': [], 'next': None, 'revision': 1, 'total': 2} | Passed |
| contract fixture 4 | {'error': 'stale'} | {'error': 'stale'} | Passed |
| contract fixture 5 | {'error': 'range'} | {'error': 'range'} | Passed |
| contract fixture 6 | {'error': 'range'} | {'error': 'range'} | Passed |
| contract fixture 7 | {'error': 'range'} | {'error': 'range'} | Passed |
| contract fixture 8 | {'error': 'range'} | {'error': 'range'} | Passed |
| contract fixture 9 | {'children': ['b'], 'next': None, 'revision': 1, 'total': 3} | {'children': ['b'], 'next': 2, 'revision': 1, 'total': 3} | Failed |
| contract fixture 10 | {'children': [], 'next': None, 'revision': 1, 'total': 1} | {'children': [], 'next': None, 'revision': 1, 'total': 1} | Passed |
SHA-256 / d7e65be29d7295160ba0bcad133045b929f5c79011e11d029d2e691f2a70c514
HELD IN THE MEMBER ARCHIVE
The verified repair and its recorded checks are member-only.
This mechanism has 10 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.
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Sign in to the archive ↗Verification & scope
Stipulated finite adapter contract, not a claim of platform accessibility or ARIA conformance. 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 2026-09-29T14:45:44.687755+00:00.
Case digest / 2271e9c641827fcf08db4259da30ab9c2dc942b91081736bdf80a8289fc2b83e