[devmotion]

ProjectTo{<:Tangent{<:Tuple}} applied to an AbstractArray checked the unprojected elements dy for all-zero instead of the projected ones dz, so elements that only become zero during projection (e.g. tangents for Bools) didn't collapse to NoTangent():

julia> ProjectTo((true, 1.0))(Any[2.0, ZeroTangent()])
Tangent{Tuple{Bool, Float64}}(NoTangent(), ZeroTangent())   # before
NoTangent()                                                  # after

Both tuple methods now check dz isa Tuple{Vararg{AbstractZero}} instead of all(d -> d isa AbstractZero, ...). This is equivalent for tuples, and the result is inferrable. Tests cover the collapse and inference for tuple and array inputs.

Split out from #724.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.63%. Comparing base (4e9c8aa) to head (11caa30).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #725      +/-   ##
==========================================
+ Coverage   93.54%   93.63%   +0.09%     
==========================================
  Files          15       15              
  Lines        1022     1022              
==========================================
+ Hits          956      957       +1     
+ Misses         66       65       -1     

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