bug: .cache() gives incorrect result when column order changes

[NickCrews]

What happened?

import ibis
ibis.options.interactive = True

t = ibis.memtable({"x": [1, 2, 3], "y": [4, 5, 6]})
t = t.cache()
t.select("x", "y").cache(), t.select("y", "x").cache()

shows

(┏━━━━━━━┳━━━━━━━┓
 ┃ x     ┃ y     ┃
 ┡━━━━━━━╇━━━━━━━┩
 │ int64 │ int64 │
 ├───────┼───────┤
 │     1 │     4 │
 │     2 │     5 │
 │     3 │     6 │
 └───────┴───────┘,
 ┏━━━━━━━┳━━━━━━━┓
 ┃ x     ┃ y     ┃
 ┡━━━━━━━╇━━━━━━━┩
 │ int64 │ int64 │
 ├───────┼───────┤
 │     1 │     4 │
 │     2 │     5 │
 │     3 │     6 │
 └───────┴───────┘)

It's like the first .cache() populates the cache with column order [x, y], and then the second call retrieves the same value.

What version of ibis are you using?

main

What backend(s) are you using, if any?

probably NA?

Relevant log output

No response

Code of Conduct

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[cpcloud]

Probably related to this equality:

In [7]: s1 = ibis.schema(dict(a="int", b="string"))

In [8]: s2 = ibis.schema(dict(b="string", a="int"))

In [9]: s1 == s2
Out[9]: True