Applying an update downloads and swaps a binary and takes minutes; the
doctor showed a spinner inside a disabled button for the whole time.
SystemActions gained a streaming CLI runner that hands each line to the
caller as it arrives, with CHAIN_PLAIN=1 set for the child so the CLI
emits one line per transition instead of its redraw-in-place block.
The update card now shows an indeterminate bar labelled with the
running step and an elapsed counter on its own timer, so the counter
keeps moving between lines that can be minutes apart. No invented
percentage: the CLI reports steps, not a measurable total.
The streaming path still defers to debugRunFaiOverride, so tests stay
hermetic and never spawn a process; three guards pin that.
Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>
