FA-98172 / Attention mask construction / Member archive
Prefix tokens cannot see the rest of their prefix · case 02
Prefix tokens cannot see the rest of their prefix.
Case contract
Positions [0,p) are a bidirectional prefix. Positions >=p attend only to suffix positions from p through the current query.
Why this case matters
A small explicit visibility matrix makes sequence-attention boundary behavior reviewable.
One recorded failure
Sample boundary fixtureThis sample comes from the broken implementation of a controlled reproducer.
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| prefix and suffix | [[true, false, false, false], [true, true, false, false], [true, true, true, false], [true, true, true, true]] | [[true, true, false, false], [true, true, false, false], [false, false, true, false], [false, false, true, true]] | Failed |
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