Database Users

[Q] [Fastboot] Can't flash Stock ROM

Hello there!
I have a Nexus 7 Device, I rooted it using a toolkit, everything was working great, then I messed up a little and I need to restore it using a Factory Image (a.k.a Stock ROM)...
The problem is, when I try to flash the .zip, it gives me the following error:
{
"lightbox_close": "Close",
"lightbox_next": "Next",
"lightbox_previous": "Previous",
"lightbox_error": "The requested content cannot be loaded. Please try again later.",
"lightbox_start_slideshow": "Start slideshow",
"lightbox_stop_slideshow": "Stop slideshow",
"lightbox_full_screen": "Full screen",
"lightbox_thumbnails": "Thumbnails",
"lightbox_download": "Download",
"lightbox_share": "Share",
"lightbox_zoom": "Zoom",
"lightbox_new_window": "New window",
"lightbox_toggle_sidebar": "Toggle sidebar"
}
According to some tutorials, you type the following commands to flash a ROM:
fastboot erase boot
fastboot erase cache
fastboot erase recovery
fastboot erase system
fastboot erase userdata
fastboot -w update ROM.zip
Click to expand...
Click to collapse
Because I'm afraid of something going wrong, I didn't erased any partition, so if for some reason the flashing procedure stops, I have the old data/partitions working because I didn't erased any, I just used the following command:
fastboot -w update ROM.zip
Click to expand...
Click to collapse
So, the questions are:
Do I need to erase the partitions first before trying to flash the Stock ROM?
Should I try flash each .img separately?
Additional Information:
Android is working, I'm able to boot with success.
Bootloader unlocked.
I didn't flashed any custom Bootloader/Recovery/ROM, everything is from Factory/Stock.
I have tested flashing the ROM under Windows and Linux (Ubuntu), it gives me the exact error.
The .zip I'm using isn't corrupted. (And it's directly from developers.google.com)
If flashing without erasing the partitions worked, I would erase them (To delete ALL data/trash) and flash it again...
P.S: First post!

I'm pretty sure the script erases those anyway... You could open it up and check though. Don't worry about the .sig files; that's normal. Check inside the .zip to make sure the system.img is actually in there. If it is, then extract it and try flashing it by itself.
In fact, if you just were trying to fix something you messed up, all you need is the system image anyway.
Sent from my Nexus 7 using Tapatalk HD

korockinout13 said:
I'm pretty sure the script erases those anyway... You could open it up and check though. Don't worry about the .sig files; that's normal. Check inside the .zip to make sure the system.img is actually in there. If it is, then extract it and try flashing it by itself.
In fact, if you just were trying to fix something you messed up, all you need is the system image anyway.
Sent from my Nexus 7 using Tapatalk HD
Click to expand...
Click to collapse
Hello!
Thanks for the answer, I tried to flash system.img and it worked, fastboot automatically erases the system partition.
I have now a clean system, thanks!
For other people with the same problem as me:
1 - Enter Fastboot Mode
2 - Extract system.img
3 - Run "fastboot flash system system.img"
4 - Enter Recovery Mode and do a "Factory Reset" (Optional, I guess)
5 - Enjoy!

Spenzert said:
fastboot automatically erases the system partition.
Click to expand...
Click to collapse
I wouldn't jump to that conclusion quite so readily.
It merely overwrote whatever contents were already there.
More or less the same result though, excepting some possibly inconsequential trash in the partition slack space.
cheers

bftb0 said:
I wouldn't jump to that conclusion quite so readily.
It merely overwrote whatever contents were already there.
More or less the same result though, excepting some possibly inconsequential trash in the partition slack space.
cheers
Click to expand...
Click to collapse
I believe fastboot really erased the partition, there's no "SuperSU" anymore and I have attached a screenshot of fastboot erasing the partition.
Cheers!

I wouldn't have believed it until I saw the picture... and now I believe! My bad!
I could swear I've done the same thing on other devices for a couple years now without the implicit erase happening. I wonder if it is a fastboot version difference.
If you don't mind me asking, what version of fastboot is that?

bftb0 said:
I wouldn't have believed it until I saw the picture... and now I believe! My bad!
I could swear I've done the same thing on other devices for a couple years now without the implicit erase happening. I wonder if it is a fastboot version difference.
If you don't mind me asking, what version of fastboot is that?
Click to expand...
Click to collapse
Android SDK Manager says "Rev. 16.0.1" (Platform-tools), maybe fastboot erased the partition first because I used "fastboot flash" instead of "fastboot update"...
A little off-topic:
I tried to root manually my Nexus and it's really easy, I might make an updated tutorial soon on how to root it manually
Have a good day!
Edit: I tried to flash TWRP (Recovery) and it didn't erased the partition first.

[Q] nexus 7 (2012) tablet, soft bricked, can't flash images, failed, unknown error

i have a Nexus 2012 7inch tablet (Wifi) that is soft bricked. (stuck at the perpetual moving colored dots screen).
when my tablet was still under warranty in 2013 it did have it's motherboard replaced when it wouldn't even turn on. now the problem is different, at least i can power it on and get into the bootloader. since the lollipop update it had been getting progressively laggy before finally 'crashing' and bootlooping.
i've tried the following:
1) first i attempted the tutorial located here: http://forums.androidcentral.com/go...1477-guide-nexus-7-factory-image-restore.html
i managed to wipe the device but not flash the images to the device.
2) then i used this tutorial http://forum.xda-developers.com/showthread.php?t=2588979 to install the adb drivers.
3) i have now used Wugs to attempt flash stock + unroot. everything seems to work until it gets to "sending 'system'" then it gives "FAILED <data transfer failure <Unknown error>>, also same error for sending 'userdata'and post-flash factory reset. same Unknown error.
i am also not sure which google images to use. i have tried nakasi 4.3 (JWR66Y), 4.4.4 (KTU84P), and 5.1.1 (LMY47V), and "any build" options.
so i'm not sure if it could be a driver issue or how to fix it further. fastboot seems to recognize the tablet while adb does not. i did not have it set in debugging mode.
i've attached the screen from Wugs...
{
"lightbox_close": "Close",
"lightbox_next": "Next",
"lightbox_previous": "Previous",
"lightbox_error": "The requested content cannot be loaded. Please try again later.",
"lightbox_start_slideshow": "Start slideshow",
"lightbox_stop_slideshow": "Stop slideshow",
"lightbox_full_screen": "Full screen",
"lightbox_thumbnails": "Thumbnails",
"lightbox_download": "Download",
"lightbox_share": "Share",
"lightbox_zoom": "Zoom",
"lightbox_new_window": "New window",
"lightbox_toggle_sidebar": "Toggle sidebar"
}

stargirl29 said:
i have a Nexus 2012 7inch tablet (Wifi) that is soft bricked. (stuck at the perpetual moving colored dots screen).
when my tablet was still under warranty in 2013 it did have it's motherboard replaced when it wouldn't even turn on. now the problem is different, at least i can power it on and get into the bootloader. since the lollipop update it had been getting progressively laggy before finally 'crashing' and bootlooping.
i've tried the following:
1) first i attempted the tutorial located here: http://forums.androidcentral.com/go...1477-guide-nexus-7-factory-image-restore.html
i managed to wipe the device but not flash the images to the device.
2) then i used this tutorial http://forum.xda-developers.com/showthread.php?t=2588979 to install the adb drivers.
3) i have now used Wugs to attempt flash stock + unroot. everything seems to work until it gets to "sending 'system'" then it gives "FAILED <data transfer failure <Unknown error>>, also same error for sending 'userdata'and post-flash factory reset. same Unknown error.
i am also not sure which google images to use. i have tried nakasi 4.3 (JWR66Y), 4.4.4 (KTU84P), and 5.1.1 (LMY47V), and "any build" options.
so i'm not sure if it could be a driver issue or how to fix it further. fastboot seems to recognize the tablet while adb does not. i did not have it set in debugging mode.
i've attached the screen from Wugs...
Click to expand...
Click to collapse
Try flashing the images individually with fastboot. That's how I always do it. Be sure your platform tools are up to date as well.

fastboot
Evolution_Tech said:
Try flashing the images individually with fastboot. That's how I always do it. Be sure your platform tools are up to date as well.
Click to expand...
Click to collapse
i'm not really sure how to do that.

stargirl29 said:
i'm not really sure how to do that.
Click to expand...
Click to collapse
Download and unzip the factory image. Unzip two times until you have all the images. I.E. bootloader, radio, boot, system, recovery, userdata, cache.
Put them where fastboot can find them. I.E. platform tools folder.
Hopefully you know how to use fastboot.
Start by flashing bootloader.
fastboot flash bootloader bootloader.img
fastboot flash radio radio.img
fastboot reboot bootloader
Then flash the rest.
fastboot flash system system.img
fastboot flash boot boot.img
fastboot flash recovery recovery.img
fastboot flash userdata userdata.img
fastboot format cache
fastboot flash cache cache.img
fastboot reboot

fastboot
Evolution_Tech said:
Download and unzip the factory image. Unzip two times until you have all the images. I.E. bootloader, radio, boot, system, recovery, userdata, cache.
Put them where fastboot can find them. I.E. platform tools folder.
Hopefully you know how to use fastboot.
Start by flashing bootloader.
fastboot flash bootloader bootloader.img
fastboot flash radio radio.img
fastboot reboot bootloader
Then flash the rest.
fastboot flash system system.img
fastboot flash boot boot.img
fastboot flash recovery recovery.img
fastboot flash userdata userdata.img
fastboot format cache
fastboot flash cache cache.img
fastboot reboot
Click to expand...
Click to collapse
no i do not know how to use fastboot. but what you posted sounds exactly like the tutorial that i followed in step #1 that i mentioned above. i did the tutorial again last night and was able to flash the images this time, but it's still stuck in bootloop on startup.

stargirl29 said:
no i do not know how to use fastboot. but what you posted sounds exactly like the tutorial that i followed in step #1 that i mentioned above. i did the tutorial again last night and was able to flash the images this time, but it's still stuck in bootloop on startup.
Click to expand...
Click to collapse
Factory reset from recovery.

Evolution_Tech said:
Factory reset from recovery.
Click to expand...
Click to collapse
if you mean this, https://support.google.com/nexus/answer/4596836?hl=en
yes. that was the first thing i did. and always the first thing i try before using any toolkits or manual repairs.
i ran Wugs again today and FINALLY got it back to the sign in screen to setup the tablet. everything was going great. then i got back into the bootloader to lock the oem. and when it restarted i'm still getting the "optimizing apps x of 99" which is annoying but it seems my tablet is at least usable for now.

Sorry to say your in the same boat as a large number of people. These devices just up and died. Take a look around for #Nexus7Bricked
Google forums will also confirm this. At this time you have a nice paperweight. I've tried all the things you have (and spent probably 10 hours over a few months) and it still won't come up.

fixed it!
vipthomps said:
Sorry to say your in the same boat as a large number of people. These devices just up and died. Take a look around for #Nexus7Bricked
Google forums will also confirm this. At this time you have a nice paperweight. I've tried all the things you have (and spent probably 10 hours over a few months) and it still won't come up.
Click to expand...
Click to collapse
i fixed it with Wugs yesterday, finally! after 5 days of trying.

[FIX] Asus Zenfone 2 Laser ZE550KL Marshmallow update problem, failed to mount /asdf

I have good experience with other phones but this is my first time working with ZE550KL.
So I took my uncle's phone and he asked me to update his phone to the latest firmware to get the VoLTE feature.
He is was on ZE550KL_WW_21.40.1220.1708 which is Marshmallow of the ZEN UI.
I have downloaded the latest firmware from the ASUS website but I couldn't update it because the recovery which came with the marshmallow update is broken.
These are the errors I got
{
"lightbox_close": "Close",
"lightbox_next": "Next",
"lightbox_previous": "Previous",
"lightbox_error": "The requested content cannot be loaded. Please try again later.",
"lightbox_start_slideshow": "Start slideshow",
"lightbox_stop_slideshow": "Stop slideshow",
"lightbox_full_screen": "Full screen",
"lightbox_thumbnails": "Thumbnails",
"lightbox_download": "Download",
"lightbox_share": "Share",
"lightbox_zoom": "Zoom",
"lightbox_new_window": "New window",
"lightbox_toggle_sidebar": "Toggle sidebar"
}
Here is what I did, and hope this works for everyone.
Hoping that you already went and searched about the problem over the internet.
These are the things you need to download :
ADB and fastboot
https://drive.google.com/file/d/0B0aDjdU4gTwZZW1HUHhqWnEteXM/view
Recovery image file
https://drive.google.com/open?id=0B0aDjdU4gTwZa1MyUmVPN3BhQjQ
Latest firmware:
https://www.asus.com/in/support/Download/39/1/0/22/ZROQURlyupei1ZQz/32/
1. Download the adb and fastboot drivers. Download the latest firmware and copy it onto your internal storage.
2. Boot into the bootloader.
3. Download the recovery image and paste it into the adb folder.
4. Now type the following command.
Code:
fastboot flash recovery recovery.img
5. This step is very important.
Now, all you have to do is hold the power button and the volume down button to boot into the installed recovery.
Remember that if you restart your phone after step 4, your old recovery(which does not work) will still be there.
6. Now select update from sdcard and select the zip file of the latest firmware you downloaded.
7. It will take at least 10 minutes to install, don't panic if you think the screen froze.
I hope this solves the issues many users are facing.
Feel free to ask questions, I will be very happy to answer.
The recovery we installed is the recovery of Android Lollipop version of the Zen UI ROM.

Thanks. It worked. The only difference is that after flashing the old recovery, my SD card was showing blank. So i selected the adb sideload option and flashed the new build.. Thanks for your guide.

Thanks but few doubts remain. The recovery you used is from Lollipop`s 1.17.40.1503 right?
Can we not do this by installing a temporary recovery image (twrp)?
I have also read elsewhere ( https://devs-lab.com/e-unable-to-mount-asdf-recovery-error-solved.html ) that you would need the boot image too. But your instructions are way too easier and easy to follow. Why don't you use boot image?
If we are using the boot image then which version of it should we use?

hellbraker said:
Thanks but few doubts remain. The recovery you used is from Lollipop`s 1.17.40.1503 right?
Can we not do this by installing a temporary recovery image (twrp)?
I have also read elsewhere ( https://devs-lab.com/e-unable-to-mount-asdf-recovery-error-solved.html ) that you would need the boot image too. But your instructions are way too easier and easy to follow. Why don't you use boot image?
If we are using the boot image then which version of it should we use?
Click to expand...
Click to collapse
Before I tried any of this... First thing I did was boot TWRP and install the lastest firmware.
But I couldn't do so because TWRP doesn't let you flash .img files.
And for the best result it is always better for you to use the official recovery to flash an official firmware.
Because ASUS f***ed up, I needed to install the previous version of the recovery to flash the firmware.
And I'm very happy that my guide worked for you.
Don't forget to give thanks. :laugh:

I haven't tried it yet. So you didn't tamper with boot.img at all. Right?
Also as previously asked what's the build number from which you extracted the recovery.img? Is it from .1503?
My current build is .1708 same as what you worked on. And will data get erased during this process?

How can I boot into the bootloader? is it by unlocking it? or is there any other non-invasive way?
Update: I installed as per your instructions. Device shows "Optimizing app 5 of 51".
Thank you.

Thank you
Thank you sir, this helped me a lot.

recovery link is asking need access plzz help

My Asus Zenfone doesn't boot anymore and doesn't even allow me to factory reset it from the bootloader. How to force reset it??

No OS installed mate 9

Hello everybody, i was handed a mate 9 handset from a friend in as is condition.
I don't know what have it been through.
The phone's back shows it is MHA-l29
Trying with buttons:-either i can enter erecovery connect to wifi. and the recovery will fail.
I can enter an interface called TRWP.
There is no OS installed on the handset apparently.
I don't know where to start, please help me. I'm willing to grasp concepts quickly, and a step by step guide will be appreciated ! thx.
Edit: i did download an "update.zip" and copied it through computed, tried to install it but got a command error...

scrutnizing said:
Hello everybody, i was handed a mate 9 handset from a friend in as is condition.
I don't know what have it been through.
The phone's back shows it is MHA-l29
Trying with buttons:-either i can enter erecovery connect to wifi. and the recovery will fail.
I can enter an interface called TRWP.
There is no OS installed on the handset apparently.
I don't know where to start, please help me. I'm willing to grasp concepts quickly, and a step by step guide will be appreciated ! thx.
Edit: i did download an "update.zip" and copied it through computed, tried to install it but got a command error...
Click to expand...
Click to collapse
Do you have adb/fastboot drivers installed? If not: https://forum.xda-developers.com/showthread.php?t=2317790
When you have that installed, boot into TWRP then tap on the Reboot button and then on the Bootloader button.
Plug in USB and open a command prompt, type the following command:
fastboot oem get-build-number
Post the result here

i solved this issue just today, i didn't get lucky with stock rom kept boot looping. What i did is get fromfuture mate 9 custom rom, place the zip in twrp folder and install zip from there.
The update.zip wouldn't install this way. At least my phone is working now.
Thanks
Edit: I also tried to flash update.app image components after extraction, using fastboot. It didn't work, I don't recommend this method.
The custom rom is life saving.

scrutnizing said:
i solved this issue just today, i didn't get lucky with stock rom kept boot looping. What i did is get fromfuture mate 9 custom rom, place the zip in twrp folder and install zip from there.
The update.zip wouldn't install this way. At least my phone is working now.
Thanks
Edit: I also tried to flash update.app image components after extraction, using fastboot. It didn't work, I don't recommend this method.
The custom rom is life saving.
Click to expand...
Click to collapse
Ah, then you're on Nougat.
The reason I asked about fastboot was to find out what build/fw you were on, then go from there to install stock firmware.
You could update to Oreo using: https://forum.xda-developers.com/mate-9/how-to/guide-mate-9-flash-update-package-t3593108

hey thanks!
The reason why im statisfied with this is that when flashing stock rom, it worked the first time (no bootloop), but the camera was not working, neither developper mode. Thats why i wiped, reflashed and got stuck in bootloop, no idea why. Also i could only flash a few of the images in update.app, very few. So it was not ideal, other images would yield an error in fastboot when flashing (command failed), i read online and figured this is perhaps due to a bad unlocking in the bootloader (if i understood correctly) at this point i felt that i could no longer process and learn info in android world, after all it was only one day that i'm into android and i felt tired, so i took the ladt chancd and decided to try the custom rom, im now satisfied with results, but many question marks are still in my head.

scrutnizing said:
hey thanks!
The reason why im statisfied with this is that when flashing stock rom, it worked the first time (no bootloop), but the camera was not working, neither developper mode. Thats why i wiped, reflashed and got stuck in bootloop, no idea why. Also i could only flash a few of the images in update.app, very few. So it was not ideal, other images would yield an error in fastboot when flashing (command failed), i read online and figured this is perhaps due to a bad unlocking in the bootloader (if i understood correctly) at this point i felt that i could no longer process and learn info in android world, after all it was only one day that i'm into android and i felt tired, so i took the ladt chancd and decided to try the custom rom, im now satisfied with results, but many question marks are still in my head.
Click to expand...
Click to collapse
It's because you can't flash everything from fastboot with just phone unlocked.
You can flash: System, vendor, boot (ramdisk and kernel for oreo), recovery (recovery_ramdisk, recovery_vendor, recovery_vbmeta for oreo), cache, userdata. (I think those are it)
Flashing anything else requires you to unlock bootloader, but it needs a special code which none of us normal people have. :/

ante0 said:
It's because you can't flash everything from fastboot with just phone unlocked.
You can flash: System, vendor, boot (ramdisk and kernel for oreo), recovery (recovery_ramdisk, recovery_vendor, recovery_vbmeta for oreo), cache, userdata. (I think those are it)
Flashing anything else requires you to unlock bootloader, but it needs a special code which none of us normal people have. :/
Click to expand...
Click to collapse
@ante0
{
"lightbox_close": "Close",
"lightbox_next": "Next",
"lightbox_previous": "Previous",
"lightbox_error": "The requested content cannot be loaded. Please try again later.",
"lightbox_start_slideshow": "Start slideshow",
"lightbox_stop_slideshow": "Stop slideshow",
"lightbox_full_screen": "Full screen",
"lightbox_thumbnails": "Thumbnails",
"lightbox_download": "Download",
"lightbox_share": "Share",
"lightbox_zoom": "Zoom",
"lightbox_new_window": "New window",
"lightbox_toggle_sidebar": "Toggle sidebar"
}
Can you give a hand, please ?
I unlocked the bootloader and flashed the recovery, the system booted successfully.
I tried to flash a ROM after that, it showed errors and didn't complete the flashing. since that time the phone has bootloop.
Unlocked bootloader and FRP
fastboot oem get-build-number : MHA-L29 8.0.0.374(C185)
I can access the TWRP recovery and erecovery and bootloader&fastboot
what I have already tried :
1-Fastboot flash ramdisk and kernel .
2-Tried to flash the stock firmware via TWRP.
3-Tried HurUpdater0.3
4- Extract update.app & HOWTA
5-Flash ramdisk and kernel from inside TWRP

is possible unbrik Mate9 Oreo , using only fastboot method ?
can help umbrik only commands fastboot?

Unlocked, can't be trusted, can only boot system via bootloader

EDIT: I don't think it's verity. I think something more is going on. I tried installing another rom with its own kernel, and the problem did not go away. So what's keeping me from getting rid of this nuissance and booting normally?
I've done some searching around to try to fix this problem, and frankly, I've got a headache now. Ok. I've got my bootloader unlocked, and I've installed TWRP and Magisk. Now I want to disable DM Verity so my device will boot normally. As it is, I have to go into the Bootloader in order to get the system to boot: no other option. Edit: Is it even verity doing this? Is it something else?
The guides for disabling dm verity have not worked. Iinstalled Magisk, and some people said that that would disable dm verity all on its own. It didn't. I installed the no-verity-opt-encrypt thing, hoping that would disable dm verity. I actually tried that option before installing Magisk. It didn't work.
Well, any ideas? Do I have the right dm verity thing? Is there more than one? Did I maybe use the one for the G5 by mistake? How do I get past this annoying thing? Please advise.

I'm not familiar with the layout of the Moto G5, so I can only relate what I've learned on Pixel devices.
I assume this is what you're seeing when you attempt to boot:
{
"lightbox_close": "Close",
"lightbox_next": "Next",
"lightbox_previous": "Previous",
"lightbox_error": "The requested content cannot be loaded. Please try again later.",
"lightbox_start_slideshow": "Start slideshow",
"lightbox_stop_slideshow": "Stop slideshow",
"lightbox_full_screen": "Full screen",
"lightbox_thumbnails": "Thumbnails",
"lightbox_download": "Download",
"lightbox_share": "Share",
"lightbox_zoom": "Zoom",
"lightbox_new_window": "New window",
"lightbox_toggle_sidebar": "Toggle sidebar"
}
What this means is that a verification error was encountered during run time. This is a function of Android Verified Boot; more details here.
Disabling dm-verity is generally done by flashing the [icode[vbmeta[/icode] image with the --disable-verity --disable-verification arguments, as such:
Code:
fastboot flash vbmeta <vbmeta image> --disable-verity --disable-verification
However, this may not apply to the Moto G5, as I'm not sure its partition structure is similar to the Pixels. Additionally, this should generally be unnecessary if you're on a stock ROM with a stock kernel.
It seems others have encountered the same problem before. It's rather wise to search before posting. Check out this thread:
Stuck at 'Your device has been unlocked and can't be trusted'. Can't enter recovery
I was flashing a rom and followed all the steps correctly: unlocked bootloader, flashed twrp, rooted and then flashed. Everything worked fine on the first go but the phone app was foreclosing instantly so i rebooted into recovery to wipe data and...
forum.xda-developers.com

No, that's not it. What happens is that when I reboot it tells me:
Your device has been unlocked and can't be trusted.
To learn more, visit:
motorola.com/unlockbootloader
ID: N/A
Your device will boot in 5 seconds.
Click to expand...
Click to collapse
And then it boots into recovery.
My device is by no means "stuck". It boots into recovery. In order to actually boot the system, I have to choose the option Reboot > Bootloader. And then when the bootloader comes up, I choose Start, and then the system boots. But this is not what I want my phone to do! I want it to, you know, behave!
There doesn't appear to be a separate vbmeta thing. There's just boot.img. AND when I tried installing a custom rom that came with its own kernel, it did not solve the problem. So something else must be going on here.
And I did everything this guy said to do regarding flashing the stock rom: https://forum.xda-developers.com/t/guide-moto-g5-plus-flashing-stock-firmware-rooting-2021.4205293/
No good. Need more help.

For anyone who goes searching desperately for a solution to this same problem: There is a workaround, and that seems to be the best we can do.
Step 1: Get the raw boot.img from your firmware package.
Step 2: Patch boot.img with Magisk. Copy it to your PC.
Step 3: Get TWRP. But you've gotta get an older version, because it's smaller. Get 3.5.0. It's going to matter in a moment.
Step 4: Reboot to Bootloader (hold Vol- while phone is turning on or rebooting).
Step 5: Use fastboot to flash the modified Boot image to the Recovery partition (fastboot flash recovery <themodifiedbootimage>). It's not where a Boot image is supposed to go, but in this case, it's what needs to happen.
Step 6: Likewise, flash TWRP to the Boot partition (fastboot flash boot <twrp.img>).
So far, that seems to work. Now, when you reboot, your phone will boot into the system like it's supposed to. If you want to launch Recovery, what you now have to do is boot into the Bootloader (see Step 4 above) and choose Start. This would normally start the system, but because TWRP is sitting in the Boot partition, it will launch TWRP instead.
I don't have a guide yet for how to make the Boot partition bigger, so that the latest version of TWRP can comfortably fit into it. And I don't know where this whole problem came from in the first place, and how to fix it the right way. But this is what we've got for now, and as far as I can tell, it works pretty well.
But remember: Your Boot and Recovery images are switched now. So any time you want to make any modifications to either, you have to remember where they are.