error multiplying matrices with entries in fraction field

@pzinn is already working on this.

Since Jul 2, 2026.

• #4462 by @pzinn — open

am I the only one encountering such issues?...
```
i1 : F=frac(QQ[y])

o1 = F

o1 : FractionField

i2 : a=matrix{{1/2}}*matrix{{y}}

o2 = | 1/2y |

1 1
o2 : Matrix F <-- F

i3 : b=matrix{{y/2}}

o3 = | y/2 |

1 1
o3 : Matrix F <-- F

i4 : a==b

o4 = false

i5 : a_(0,0)===b_(0,0)

o5 = false

i6 : ring a===ring b

o6 = true

i7 : source a===source b

o7 = true

i8 : target a===target b

o8 = true

i9 : a-b==0

o9 = true
```

Reproduce the reported transcript involving Matrix values over a FractionField, comparing matrix equality, entry identity, and subtraction. Start by tracing the matrix and FractionField equality entry points; done means the two mathematically equal matrices have consistent equality behavior without breaking the demonstrated subtraction result.

Written by the indexing model from the issue text.