The save dialog asks before replacing only the file it answers with.
After it closes, pick_save can change that path: it gives a name
without an extension the suggested file's extension (#5039), and
Lowercase Extension changes CAT.PSD to CAT.psd. The save then wrote to
the changed path at once, and a file there was replaced without a
question. On Linux this happens when the Swatches panel exports to a
folder that holds Swatches.aco (the one-type portal dialog shows and
asks about "Swatches"), when CAT.PSD is typed where CAT.psd exists, and
in rfd's zenity fallback dialog.
When the path written differs from the dialog's answer and a file
exists there, the save now asks "“{name}” already exists. Replace it?".
Replace writes the file, and ui.dialog.confirm returns the save's
result. Cancel writes nothing and ends the save like the dialog's
Cancel, and Save in the close prompt of an untitled document returns
to that prompt. PhotoCraft counts the file dialog as open until the
question is answered.
A name that reaches the same file, as CAT.PSD and CAT.psd do on
Windows and macOS by default, is not asked about again. The new
same_file service decides this: the desktop app compares device and
inode on Unix and the canonical paths on Windows. The web has no file
stamps and does not ask. The two new strings have rows in all 20
catalogs.