[devmotion]

ProjectTo{Hermitian} kept the imaginary part of a Diagonal tangent, so the result was not Hermitian and differed from projecting the same tangent as a dense Matrix (#722).

The Diagonal method now takes the real part of the projected diagonal with oftype(y, real(y)), the same as LinearAlgebra.hermitian(::Number). Using oftype instead of complex keeps the element type for any number type. I checked locally that quaternions (Quaternions.jl) and complex Unitful quantities give the same result as the dense path; they are not test dependencies, so that check is not in the test suite.

• If the tangent or the projected diagonal is already real, it is returned without taking the real part again. So Hermitian{Float64} still projects a Diagonal{Float64} without allocating, and a real tangent onto a complex Hermitian is copied only once (new @ballocated tests).
• The Symmetric method is unchanged; a new test checks that it keeps a complex diagonal.
• Tests cover ComplexF64 and ComplexF32, a real tangent for a complex Hermitian, a real Hermitian with a complex tangent, agreement with the dense path, and the size check.
• Bumps the version to 1.26.7.

Found while reviewing JuliaDiff/ChainRules.jl#856, which switched the Matrix(::Hermitian) rules to ProjectTo.

Fixes #722.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.54%. Comparing base (2a1e65e) to head (1a2a559).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #723      +/-   ##
==========================================
+ Coverage   93.50%   93.54%   +0.03%     
==========================================
  Files          15       15              
  Lines        1016     1022       +6     
==========================================
+ Hits          950      956       +6     
  Misses         66       66              

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.