Every Nth boot lands in the bootloader" is a retry countdown, not a glitch

scope: generic · severity: trap · confidence: proven · subsystem: boot

On an A/B device, fastboot set_active <slot> arms that slot with a fixed number of boot retries (3 on taimen) and clears unbootable.

Nothing in pmOS ever reports a boot successful. So the bootloader scores every boot as failed and decrements the counter. At 0 it stops handing off and keeps the device.

That is the entire “roughly every 3rd boot lands in the bootloader by itself” cadence. It is a countdown, not a glitch, and it is also the only reliable way into the bootloader from software if the syscall path is unavailable.

Always set_active before rebooting out of the bootloader. set_active resets the counter and clears unbootable; a bare fastboot reboot from a counter already at 0 drops straight back into the bootloader. That is the single most common “the phone is stuck in fastboot” confusion, and it looks like a hardware fault.

Record PORTHOLE_BOOT_RETRIES in the profile so the number is discoverable, and PORTHOLE_SLOT_FORBIDDEN for any slot with no known-good image — porthole refuses to set_active that one rather than trusting you to remember at 3am.