"no valid slot to boot" on locked bootloader

Using the Google Factory Image of Android 10 for the Pixel 4 (flame), I ran into trouble: the device does not boot with the following reason:

no valid slot to boot

I hence tried to flash another OS image but unfortunately, the bootloader is locked. Even Google's own Factory Images don't flash.

$ fastboot flashing get_unlock_ability

(bootloader) get_unlock_ability: 0

OKAY [  0.093s]

Finished. Total time: 0.093s

Is there any way to flash the factory image anyway?

$ fastboot getvar all

(bootloader) product:flame

(bootloader) serialno:99051FFAZ006PC

(bootloader) variant:SM8 UFS

(bootloader) max-download-size:0x10000000

(bootloader) slot-suffixes:_a,_b

(bootloader) version-bootloader:c2f2-0.3-6863466

(bootloader) version-baseband:g8150-00075-201008-B-6891495

(bootloader) secure-boot:PRODUCTION

(bootloader) secure:yes

(bootloader) hw-revision:MP1.0

(bootloader) is-userspace:no

(bootloader) slot-count:2

(bootloader) current-slot:a

(bootloader) unlocked:no

(bootloader) nos-production:yes

(bootloader) off-mode-charge:1

(bootloader) slot-retry-count:a:0

(bootloader) slot-unbootable:a:yes

(bootloader) slot-successful:a:no

(bootloader) slot-retry-count:b:0

(bootloader) slot-unbootable:b:yes

(bootloader) slot-successful:b:no

(bootloader) battery-voltage:4258

(bootloader) battery-soc-ok:yes

(bootloader) snapshot-update-status:none

(bootloader) storage-vendor:MICRON

(bootloader) storage-model:64GB-UFS-MT

(bootloader) storage-rev:8QSP

(bootloader) citadel-fw:0.0.3/brick_v0.0.7758-a9dacb5c9 2020-01-15 21:24:

(bootloader) auto-shutdown:0

(bootloader) partition-type:ssd:raw

(bootloader) partition-size:ssd:0x2000

(bootloader) partition-type:persist:raw

(bootloader) partition-size:persist:0x2000000

(bootloader) partition-type:misc:raw

(bootloader) partition-size:misc:0x100000

(bootloader) partition-type:keystore:raw

(bootloader) partition-size:keystore:0x80000

(bootloader) partition-type:frp:raw

(bootloader) partition-size:frp:0x80000

(bootloader) partition-type:boot_a:raw

(bootloader) partition-size:boot_a:0x4000000

(bootloader) partition-type:boot_b:raw

(bootloader) partition-size:boot_b:0x4000000

(bootloader) partition-type:modem_a:raw

(bootloader) partition-size:modem_a:0x6000000

(bootloader) partition-type:modem_b:raw

(bootloader) partition-size:modem_b:0x6000000

(bootloader) partition-type:klog:raw

(bootloader) partition-size:klog:0x800000

(bootloader) partition-type:metadata:raw

(bootloader) partition-size:metadata:0x1000000

(bootloader) partition-type:vbmeta_system_a:raw

(bootloader) partition-size:vbmeta_system_a:0x10000

(bootloader) partition-type:vbmeta_system_b:raw

(bootloader) partition-size:vbmeta_system_b:0x10000

(bootloader) partition-type:super:raw

(bootloader) partition-size:super:0x245800000

(bootloader) partition-type:userdata:raw

(bootloader) partition-size:userdata:0xC7FFFB000

(bootloader) partition-type:xbl_a:raw

(bootloader) partition-size:xbl_a:0x380000

(bootloader) partition-type:xbl_config_a:raw

(bootloader) partition-size:xbl_config_a:0x20000

(bootloader) partition-type:xbl_b:raw

(bootloader) partition-size:xbl_b:0x380000

(bootloader) partition-type:xbl_config_b:raw

(bootloader) partition-size:xbl_config_b:0x20000

(bootloader) partition-type:ALIGN_TO_128K_1:raw

(bootloader) partition-size:ALIGN_TO_128K_1:0x1A000

(bootloader) partition-type:cdt:raw

(bootloader) partition-size:cdt:0x20000

(bootloader) partition-type:ddr:raw

(bootloader) partition-size:ddr:0x100000

(bootloader) partition-type:aop_a:raw

(bootloader) partition-size:aop_a:0x80000

(bootloader) partition-type:tz_a:raw

(bootloader) partition-size:tz_a:0x400000

(bootloader) partition-type:hyp_a:raw

(bootloader) partition-size:hyp_a:0x84000

(bootloader) partition-type:abl_a:raw

(bootloader) partition-size:abl_a:0x200000

(bootloader) partition-type:keymaster_a:raw

(bootloader) partition-size:keymaster_a:0x80000

(bootloader) partition-type:cmnlib_a:raw

(bootloader) partition-size:cmnlib_a:0x80000

(bootloader) partition-type:cmnlib64_a:raw

(bootloader) partition-size:cmnlib64_a:0x80000

(bootloader) partition-type:devcfg_a:raw

(bootloader) partition-size:devcfg_a:0x20000

(bootloader) partition-type:qupfw_a:raw

(bootloader) partition-size:qupfw_a:0x14000

(bootloader) partition-type:vbmeta_a:raw

(bootloader) partition-size:vbmeta_a:0x10000

(bootloader) partition-type:dtbo_a:raw

(bootloader) partition-size:dtbo_a:0x800000

(bootloader) partition-type:uefisecapp_a:raw

(bootloader) partition-size:uefisecapp_a:0x200000

(bootloader) partition-type:imagefv_a:raw

(bootloader) partition-size:imagefv_a:0x200000

(bootloader) partition-type:apdp_a:raw

(bootloader) partition-size:apdp_a:0x10000

(bootloader) partition-type:msadp_a:raw

(bootloader) partition-size:msadp_a:0x10000

(bootloader) partition-type:multiimgoem_a:raw

(bootloader) partition-size:multiimgoem_a:0x8000

(bootloader) partition-type:aop_b:raw

(bootloader) partition-size:aop_b:0x80000

(bootloader) partition-type:tz_b:raw

(bootloader) partition-size:tz_b:0x400000

(bootloader) partition-type:hyp_b:raw

(bootloader) partition-size:hyp_b:0x84000

(bootloader) partition-type:abl_b:raw

(bootloader) partition-size:abl_b:0x200000

(bootloader) partition-type:keymaster_b:raw

(bootloader) partition-size:keymaster_b:0x80000

(bootloader) partition-type:cmnlib_b:raw

(bootloader) partition-size:cmnlib_b:0x80000

(bootloader) partition-type:cmnlib64_b:raw

(bootloader) partition-size:cmnlib64_b:0x80000

(bootloader) partition-type:devcfg_b:raw

(bootloader) partition-size:devcfg_b:0x20000

(bootloader) partition-type:qupfw_b:raw

(bootloader) partition-size:qupfw_b:0x14000

(bootloader) partition-type:vbmeta_b:raw

(bootloader) partition-size:vbmeta_b:0x10000

(bootloader) partition-type:dtbo_b:raw

(bootloader) partition-size:dtbo_b:0x800000

(bootloader) partition-type:uefisecapp_b:raw

(bootloader) partition-size:uefisecapp_b:0x200000

(bootloader) partition-type:imagefv_b:raw

(bootloader) partition-size:imagefv_b:0x200000

(bootloader) partition-type:apdp_b:raw

(bootloader) partition-size:apdp_b:0x10000

(bootloader) partition-type:msadp_b:raw

(bootloader) partition-size:msadp_b:0x10000

(bootloader) partition-type:multiimgoem_b:raw

(bootloader) partition-size:multiimgoem_b:0x8000

(bootloader) partition-type:devinfo:raw

(bootloader) partition-size:devinfo:0x1000

(bootloader) partition-type:spunvm:raw

(bootloader) partition-size:spunvm:0x800000

(bootloader) partition-type:splash:raw

(bootloader) partition-size:splash:0x8000

(bootloader) partition-type:limits:raw

(bootloader) partition-size:limits:0x1000

(bootloader) partition-type:toolsfv:raw

(bootloader) partition-size:toolsfv:0x100000

(bootloader) partition-type:logfs:raw

(bootloader) partition-size:logfs:0x800000

(bootloader) partition-type:storsec:raw

(bootloader) partition-size:storsec:0x20000

(bootloader) partition-type:uefivarstore:raw

(bootloader) partition-size:uefivarstore:0x80000

(bootloader) partition-type:secdata:raw

(bootloader) partition-size:secdata:0x7000

(bootloader) partition-type:ALIGN_TO_128K_2:raw

(bootloader) partition-size:ALIGN_TO_128K_2:0x1A000

(bootloader) partition-type:modemst1:raw

(bootloader) partition-size:modemst1:0x200000

(bootloader) partition-type:modemst2:raw

(bootloader) partition-size:modemst2:0x200000

(bootloader) partition-type:fsg:raw

(bootloader) partition-size:fsg:0x200000

(bootloader) partition-type:fsc:raw

(bootloader) partition-size:fsc:0x20000

(bootloader) partition-type:system_a:raw

(bootloader) partition-size:system_a:0x30FFC000

(bootloader) partition-type:system_b:raw

(bootloader) partition-size:system_b:0x173E000

(bootloader) partition-type:vendor_a:raw

(bootloader) partition-size:vendor_a:0x2DBC3000

(bootloader) partition-type:vendor_b:raw

(bootloader) partition-size:vendor_b:0x0

(bootloader) partition-type:product_a:raw

(bootloader) partition-size:product_a:0x7D6CA000

(bootloader) partition-type:product_b:raw

(bootloader) partition-size:product_b:0x28DAC000

(bootloader) partition-type:system_ext_a:raw

(bootloader) partition-size:system_ext_a:0xE9A1000

(bootloader) partition-type:system_ext_b:raw

(bootloader) partition-size:system_ext_b:0x0

all: 

Finished. Total time: 0.296s

Since OEM unlocking is not enabled in Developer options, and the bootloader is not unlocked, your options a limited.

The first (although not preferred option in most cases) is to contact Google support for an RMA on your device to get a replacement. This is usually a simple thing and they usually handle it quite well. You can find information on this to check the status of your warranty and start a claim here.

The only other alternative you have at this point is attempting to flash an OTA image manually. An OTA image is what is sent to the device for an Over The Air update, and is usually pretty safe to install, but we are going to do it manually. Note that flashing an OTA image is not the same as doing a full firmware image flash, so some things on your device need to be in place even if the device is not in a bootable state. I don't know these exact items, but if they are not there the updater script will fail. I am also going to assume that you have Android Platform Tools installed and working (as you have output of fastboot working, it appears so).

The details and files are supplied by Google for Pixel (and older Nexus devices) on their developer site in the full OTA section for Pixel devices linked here, but just make sure you select the correct device you can see this on the previously linked page if you know your model such as Pixel 4 or by performing a fastboot getvar all and looking at the (bootloader) product: field... For you with a Pixel 4 it will be "flame".

Here are the essential steps, more detailed information is in the links above:

Download the OTA ZIP file from the above page, and know where it is located but do NOT unzip the file. Note you should always select the newest one listed for your device which will typically be at the bottom of your device section.

Boot your device into fastboot mode and connect the USB cable

Select Recovery from the menu and press POWER to select it. Wait for the Android logo with a red Exclamation mark to appear on the screen

Access the recovery menu with POWER+VOL UP

Select Apply update from ADB from the menu and press POWER

Test your USB connection with adb devices which should output your device with sideload next to it. If the result is anything else, you need to troubleshoot your USB connection or software installation before continuing.

Enter adb sideload ota_file.zip where ota_file.zip is the full path and filename of the OTA ZIP file you downloaded previously

The device will download and verify the file, then flash it to your device, then make that software "slot" active. If all goes well, after several minutes a success confirmation will be displayed and you will be presented with a menu.

Select Reboot system now and wait for the phone to boot up fully.

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