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FA-98211 / Attention mask construction / Open access

Sliding window stops after the initial query rows · case 01

Sliding window stops after the initial query rows.

Verified by executionVariant 1 · 6 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Query eligibility is based on distance from sequence start, so later queries lose visibility.

THE FAILURE

Query eligibility is based on distance from sequence start, so later queries lose visibility.

Unsuccessful approach: Adding a query-relative lower bound but shifting it one extra position still drops the oldest allowed key.

Case contract

For each query i in a sequence of length L, visible keys are max(0,i-W+1)..i; W<=0 means none.

Why this case matters

A small explicit visibility matrix makes sequence-attention boundary behavior reviewable.

1 / The failure

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

N = 1
observations = []
def solve(length, window):
    return [[j<=i and i<window for j in range(length)] for i in range(length)]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('moving boundary',solve(N+3,2),[[2>0 and max(0,i-1)<=j<=i for j in range(N+3)] for i in range(N+3)])
check('window one',solve(3,1),[[True,False,False],[False,True,False],[False,False,True]])
check('zero window',solve(2,0),[[False,False],[False,False]])
check('oversized window',solve(2,9),[[True,False],[True,True]])
check('empty sequence',solve(0,1),[])
check('last query',solve(4,3)[3],[False,True,True,True])
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
moving boundary[[True, False, False, False], [True, True, False, False], [False, False, False, False], [False, False, False, False]][[True, False, False, False], [True, True, False, False], [False, True, True, False], [False, False, True, True]]Failed
window one[[True, False, False], [False, False, False], [False, False, False]][[True, False, False], [False, True, False], [False, False, True]]Failed
zero window[[False, False], [False, False]][[False, False], [False, False]]Passed
oversized window[[True, False], [True, True]][[True, False], [True, True]]Passed
empty sequence[][]Passed
last query[False, False, False, False][False, True, True, True]Failed

SHA-256 / 4bfd6d3c9c4ec029f79e7ba69a60a5b0c5b0bdbe218fe164222c38b45bcf00a0

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(length, window):
    return [[window>0 and max(0,i-window+2)<=j<=i for j in range(length)] for i in range(length)]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('moving boundary',solve(N+3,2),[[2>0 and max(0,i-1)<=j<=i for j in range(N+3)] for i in range(N+3)])
check('window one',solve(3,1),[[True,False,False],[False,True,False],[False,False,True]])
check('zero window',solve(2,0),[[False,False],[False,False]])
check('oversized window',solve(2,9),[[True,False],[True,True]])
check('empty sequence',solve(0,1),[])
check('last query',solve(4,3)[3],[False,True,True,True])
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
moving boundary[[True, False, False, False], [False, True, False, False], [False, False, True, False], [False, False, False, True]][[True, False, False, False], [True, True, False, False], [False, True, True, False], [False, False, True, True]]Failed
window one[[False, False, False], [False, False, False], [False, False, False]][[True, False, False], [False, True, False], [False, False, True]]Failed
zero window[[False, False], [False, False]][[False, False], [False, False]]Passed
oversized window[[True, False], [True, True]][[True, False], [True, True]]Passed
empty sequence[][]Passed
last query[False, False, True, True][False, True, True, True]Failed

SHA-256 / 53a49bd51313d9c29c04a19be4b05c2e823c96d26d8eece84b835e785ce1b669

HELD IN THE MEMBER ARCHIVE

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

This mechanism has 6 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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Verification & scope

These are toy Boolean matrix contracts; they do not define a production model architecture or tensor library behavior. 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 2026-09-30T16:48:10.629747+00:00.

Case digest / 8780f666c4d975a14283260d9a0d1dc3cebdb6f39268840121b8005a7492ab0a