[OnePlus 6 ROMs, Kernels, Recoveries, & Other Devel] Ufos92:
The bi-annual flash, brick, repeat journey begins. Let's document all the things that can go wrong.

Prologue.

Reddit had a heated debate on how it's not advised to upgrade to android 10 before flashing LineageOS.

So, after I unboxed my new opo6 I upgraded through OTA to android9 and stopped.

Episode I.

copy files to the phone (useless)

`fastboot oem unlock` (wipes data, oopsie)

copy files again

`fastboot boot twrp-3.3.1-2-enchilada.img`

flash twrp zip -- all good so far, reboots into system and recover

flash `lineage-17.1-20200121_121543-UNOFFICIAL-enchilada.zip`

soft-brick, even twrp stopped working. ooopsie...

Episode II

Unbricking through fastboot gets stuck at `fastboot boot twrp.img`

(I did re-flash all the partitions tho, I even have a ****ty "powered by android" logo now)

no version of twrp or stock recovery works with `fastboot boot myass.img`, keyword being `boot`.

`fastboot flash twrp-whatever.img` -- same result, soft brick. Black screen, blue light.

something tells me I'll have to find a windows pc...

And since we're gonna be unbricking through MSM, let's try something crazy

`fastboot --set-active=b`

`fastboot flash boot oos_10.3.0_stock_boot.img` -- lastes stable (I guess?..)

Wow, stock image of oxygen with android10 now works, wifi works, phone reboots.

Episode III

some background on the following A/B mess can be found here (I haven't read thoroughly)

`fastboot boot twrp-3.3.1-16-enchilada-Q-mauronofrio.img` -- still doesn't work

`fastboot --set-active=a` -- brick

`fastboot --set-active=b` -- back to normal

`fastboot flash boot_b twrp-3.3.1-16-enchilada-Q-mauronofrio.img` -- bricks

`fastboot flash boot_a twrp-3.3.1-16-enchilada-Q-mauronofrio.img` -- still brick

`fastboot --set-active=b` -- loads TWRP (rrright, we flashed it instead of the OS, remember?...). It even remebers my settings. Wait, didn't we re-flash all the partitions? Nevermind...

repeat Episode I and we're back to square one.

Episode IV

Re-flashed all partitions from the official recovery guide again. Actually that also boots me into oos10.3.

`fastboot --set-active=a`

`fastboot boot twrp-3.3.1-16-enchilada-Q-mauronofrio.img` -- now consistently works even after wiping everything but storage

More mess around, wiped everything, reflashed partitions, reflashed OSS, vaugely followed this post

https://xdaforums.com/showpost.php?p=80294695&postcount=204

without installing TWRP/Gapps/Magisk in the end.

It boots...

Episode V

Interesting, I now have android stock recovery. Looks like this

`fastboot boot twrp.ing` works

`fastboot flash boot twrp.img` does nothing, I guess it's the wrong partition again :D

Flashing into `a` doesn't work "FAILED (remote: (recovery_a) No such partition)"

Now I remember that we have to flash twrp from twrp itself. Which, btw, in the log also tells you that it patches both partitions.

I finally got the usual TWRP + LineageOS setup.

Episode VI

Flashed Gapps `open_gapps-arm64-10.0-nano-20200127.zip` -- still good, except I now have some bloatware on my phone :D

Flashed Magisk `Magisk-v20.3.zip` -- still good!

Conclusion

A/B is a mess.

Sometimes you need to flash both in order to get something working.

The installation guide in the header is highly misleading. The actual working guide is in this thread on the page #20.

---- WORKING GUIDE -----

https://xdaforums.com/showpost.php?p=81517291&postcount=742

Was all the time in the neighboring thread. Most of the "unnecessary" steps from it I've learned the hard way.