There should be no requirement for this. Columns in relations are not conceptually ordered, so it shouldn't matter for the things you're doing with the data anyway, and the database should be able to reorder the data in whatever way it likes, since desire to isolate the user from physical data structures was one of the main reasons for the rise of RDBMS.
2. postgres definitely does not, and column tetris is absolutely a thing in the same way struct packing is (with the additional complexity of variable-size columns)
And what PostgreSQL does is of course an implementation detail of PostgreSQL.
My point was that you’re trying to prevent the DB from reordering the data because there’s a performance cost when that happens.
Sure. “Reduce the need” would be a better word than “prevent”.
If I can do a good job organizing the table columns (as described above) it’ll lower the need for the DB to reorder data.
Reduced need to reorder, improves performance.