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FA-98196 / Attention mask construction / Open access

Global tokens are incorrectly limited by local window · case 01

Global tokens are incorrectly limited by local window.

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

ROOT CAUSE

A uniform sliding window ignores explicitly global key positions.

THE FAILURE

A uniform sliding window ignores explicitly global key positions.

Unsuccessful approach: Shrinking the local window by one underfills ordinary rows even after global keys are admitted.

Case contract

Causal local window W; any listed global key <= query is visible at any distance.

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, global_keys):
    return [[window>0 and 0<=i-j<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})
g=[0]
check('old global key',solve(N+2,2,g),[[j<=i and (j in g or (2>0 and i-j<2)) for j in range(N+2)] for i in range(N+2)])
check('no globals',solve(3,2,[]),[[j<=i and i-j<2 for j in range(3)] for i in range(3)])
check('global future still hidden',solve(3,1,[2])[0],[True,False,False])
check('zero window global only',solve(3,0,[0]),[[j==0 and j<=i for j in range(3)] for i in range(3)])
check('empty sequence',solve(0,2,[]),[])
check('global old key at last row',solve(4,1,[0])[3],[True,False,False,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
old global key[[True, False, False], [True, True, False], [False, True, True]][[True, False, False], [True, True, False], [True, True, True]]Failed
no globals[[True, False, False], [True, True, False], [False, True, True]][[True, False, False], [True, True, False], [False, True, True]]Passed
global future still hidden[True, False, False][True, False, False]Passed
zero window global only[[False, False, False], [False, False, False], [False, False, False]][[True, False, False], [True, False, False], [True, False, False]]Failed
empty sequence[][]Passed
global old key at last row[False, False, False, True][True, False, False, True]Failed

SHA-256 / adbb996f0389cad51c6f1e84bb969458c95b49dd0d04f254afdbda11ff892481

2 / The unsuccessful fix

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

N = 1
observations = []
def solve(length, window, global_keys):
    return [[j<=i and (j in global_keys or i-j<window-1) 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})
g=[0]
check('old global key',solve(N+2,2,g),[[j<=i and (j in g or (2>0 and i-j<2)) for j in range(N+2)] for i in range(N+2)])
check('no globals',solve(3,2,[]),[[j<=i and i-j<2 for j in range(3)] for i in range(3)])
check('global future still hidden',solve(3,1,[2])[0],[True,False,False])
check('zero window global only',solve(3,0,[0]),[[j==0 and j<=i for j in range(3)] for i in range(3)])
check('empty sequence',solve(0,2,[]),[])
check('global old key at last row',solve(4,1,[0])[3],[True,False,False,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
old global key[[True, False, False], [True, True, False], [True, False, True]][[True, False, False], [True, True, False], [True, True, True]]Failed
no globals[[True, False, False], [False, True, False], [False, False, True]][[True, False, False], [True, True, False], [False, True, True]]Failed
global future still hidden[False, False, False][True, False, False]Failed
zero window global only[[True, False, False], [True, False, False], [True, False, False]][[True, False, False], [True, False, False], [True, False, False]]Passed
empty sequence[][]Passed
global old key at last row[True, False, False, False][True, False, False, True]Failed

SHA-256 / c6fe4cd3455e3dbf49bbcee32f8fd09fb4655c28451d73110b5ff39c729b487d

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 2026-09-30T16:48:10.194056+00:00.

Case digest / cbc6ac208fd92a8f907aab6c209228744d91757e7090cff858baf31c824f2d08