1. it must be enabled by any presence of power.

Maybe a short glitch cause restarting the CPU but was to short to trigger a full power on reset. Then the CPU starts from anywhere and the WD enable was never executed.
Such a glitch (incomplete reset) will not disable the WD, so no problem. ALSO: if you can not avoid enabling (note NOT "disable") the WD you can not use an ICE.

So if lowest power consumption wins against reliability, then let the watchdog fuse unprogrammed and enable/disable the watchdog by software.
Again enable YES, disable NO

Erik