truncateMiddle/truncateLeft return longer strings than their budget in narrow terminals #41054

truncateLeft and truncateMiddle in packages/tui/src/util/locale.ts compute a slice length that hits zero or goes negative on small budgets. String.prototype.slice(-0) returns the whole string, so both helpers can return something longer than what they were given:

truncateMiddle("abcdefghij", -1) -> "abcdefghi…bcdefghij"   (19 chars from a 10 char input)
truncateMiddle("abcdefghij",  0) -> "…bcdefghij"
truncateMiddle("abcdefghij",  1) -> "…abcdefghij"
truncateLeft("abcdefghij",   1)  -> "…abcdefghij"

This hits real call sites in narrow terminals. Running the actual expressions from the TUI against the real module:

term | callsite                     | budget | out.len
  10 | dialog-select.tsx:702        |      1 |      40   <- OVERFLOW
  12 | dialog-move-session.tsx:151  |      1 |      40   <- OVERFLOW
  14 | dialog-select.tsx:702        |      2 |      41   <- OVERFLOW
  16 | dialog-move-session.tsx:151  |      2 |      41   <- OVERFLOW

The Math.max(1, ...) at those call sites looks like a guard but clamps right into the broken range. files.tsx:35 uses Math.max(2, ...), which happens to land just outside it.

So the truncate helpers grow the string exactly when the terminal has the least room, and the layout blows out instead of being protected.

Clamping inside the helpers fixes all call sites at once. util/locale.ts currently has no tests. Happy to send a PR with both.