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Pepijn
0d88eaf8eb
Regression coverage for the text-CE collapse bug fixed in 3cd348ff.
Pure-function tests over ``_mark_target_span_causal`` /
``_locate_lang_range`` / ``make_att_2d_masks`` — no model load, fast.
Pins:
* the target span flips to att=1, prompt/images stay att=0;
* target tokens attend causally among themselves (no peeking at
future targets) — genuine next-token prediction;
* targets still attend bidirectionally to images + the user prompt;
* the action-expert (state) token still attends to every target;
* a no-target subtask (low_level_execution user turn, labels all
-100) leaves the mask bidirectional;
* an explicit test documenting the bug: the raw embed_prefix mask
lets the first target token see the last — the copy-task collapse.
Skips cleanly when transformers isn't installed.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>