Why are four Password variants identical to Default?
Because an empty password field is a text field. Same placeholder, same border, same height. Only Filled and Invalid (Filled) differ, showing dots instead of characters, because only then is there something to hide. The duplication is the correct answer rather than a shortcut.
What does Focus do to the border?
Nothing. It keeps the 1px base.input line exactly where it was and adds a 3px base.ring outside it. Swapping the border for a ring would make a focused field a different shape from an unfocused one; adding to it keeps focus reading as the same event it is on every other control in the kit.
What is the difference between Invalid and Invalid (Filled)?
Both take the border to base.destructive. Only the filled one takes the text there too. A field flagged on submit while still empty keeps its muted placeholder, because the placeholder is not the thing that failed validation - the absence of a value is.
Why is File the only variant with two pieces of text?
It carries a 74-wide "Choose file" label at 14/500 in base.foreground, then the filename beside it at 14/400. That label is a button in the browser and a fixed-width block here, which is why the File column's value text is 269 wide against everyone else's 349.