The rebased synthetic guard built a bare dict that main's _build_payload
no longer accepts (it indexes aspect_ratios/resolutions directly) and never
exercised generate(); it now builds the family via _family() and asserts
generate() returns modality_unsupported without submitting. The surface
matrix's i2v-only parametrization collected zero cases after Gemini Omni
Flash 1.1 gained t2v, so it is removed along with the dead branch in the
t2v matrix.
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