Can't Flash Google Factory Image - No Boot Partition
Well I'm into TWRP but still things awry, but this post is resolved. I had to specify boot_a or it tried to use boota.

fastboot format:ext4 boot_a
fastboot flash boot_a boot.img


Finally got fully back to stock, which is what I like to do after a soft brick. I did it by manually typing fastboot flash foo_a foo.img for EVERY IMAGE. Then I finished by re-locking the bootloader.

Note: It's scary to lock bootloader while softbricked but I can confirm I have locked/failed to fix brick/re-unlocked bootloader from Fastboot. As long as your "brick" starts with the bootloader unlocked you should be good!

Here is my rediclous fix of my problem:

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot flash boot boot.img
target reported max download size of 536870912 bytes
sending 'boota' (40960 KB)...
OKAY [  0.156s]
writing 'boota'...
FAILED (remote: No such partition.)
finished. total time: 0.156s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot --slot:boot_aflash boot boot.img
fastboot: unknown option -- slot:boot_aflash

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot --slot:boot_a flash boot boot.img
fastboot: unknown option -- slot:boot_a

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot --slot boot_a flash boot boot.img
Slot boot_a does not exist. supported slots are:
a
b


C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot --slot a flash boot boot.img
target reported max download size of 536870912 bytes
sending 'boota' (40960 KB)...
OKAY [  0.172s]
writing 'boota'...
FAILED (remote: No such partition.)
finished. total time: 0.172s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot --slot all flash boot boot.img
target reported max download size of 536870912 bytes
sending 'boota' (40960 KB)...
OKAY [  0.156s]
writing 'boota'...
FAILED (remote: No such partition.)
finished. total time: 0.172s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot erase boot
erasing 'boota'...
FAILED (remote: Check device console.)
finished. total time: 0.000s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot erase boot_a
erasing 'boot_a'...
OKAY [  0.016s]
finished. total time: 0.031s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot erase boot_b
erasing 'boot_b'...
OKAY [  0.016s]
finished. total time: 0.016s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot flash boot_a boot.img
target reported max download size of 536870912 bytes
sending 'boot_a' (40960 KB)...
OKAY [  0.156s]
writing 'boot_a'...
OKAY [  0.577s]
finished. total time: 0.733s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot flash boot_b boot.img
target reported max download size of 536870912 bytes
sending 'boot_b' (40960 KB)...
OKAY [  0.172s]
writing 'boot_b'...
OKAY [  0.562s]
finished. total time: 0.750s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash bootloader bootloader-taimen-tmz20k.img
target reported max download size of 536870912 bytes
sending 'bootloaderb' (36336 KB)...
OKAY [  0.141s]
writing 'bootloaderb'...
OKAY [  0.531s]
finished. total time: 0.672s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot reboot-bootloader
rebooting into bootloader...
OKAY [  0.000s]
finished. total time: 0.000s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot flash radio_a radio-taimen-g8998-00253-1809191716.img
target reported max download size of 536870912 bytes
sending 'radio_a' (60388 KB)...
OKAY [  0.219s]
writing 'radio_a'...
OKAY [  0.859s]
finished. total time: 1.078s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot flash radio_b radio-taimen-g8998-00253-1809191716.img
target reported max download size of 536870912 bytes
sending 'radio_b' (60388 KB)...
OKAY [  0.235s]
writing 'radio_b'...
OKAY [  0.859s]
finished. total time: 1.094s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot reboot-bootloader
rebooting into bootloader...
OKAY [  0.000s]
finished. total time: 0.000s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash boot_a boot.img
target reported max download size of 536870912 bytes
sending 'boot_a' (40960 KB)...
OKAY [  0.156s]
writing 'boot_a'...
OKAY [  0.547s]
finished. total time: 0.703s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash boot_b boot.img
target reported max download size of 536870912 bytes
sending 'boot_b' (40960 KB)...
OKAY [  0.156s]
writing 'boot_b'...
OKAY [  0.750s]
finished. total time: 0.906s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash vendor_a vendor.img
target reported max download size of 536870912 bytes
erasing 'vendor_a'...
OKAY [  0.030s]
sending 'vendor_a' (360328 KB)...
OKAY [  1.339s]
writing 'vendor_a'...
OKAY [  1.563s]
finished. total time: 2.931s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash vendor_b vendor.img
target reported max download size of 536870912 bytes
erasing 'vendor_b'...
OKAY [  0.031s]
sending 'vendor_b' (360328 KB)...
OKAY [  1.354s]
writing 'vendor_b'...
OKAY [  1.542s]
finished. total time: 2.943s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash system_a system.img
target reported max download size of 536870912 bytes
erasing 'system_a'...
OKAY [  0.078s]
sending sparse 'system_a' 1/5 (524284 KB)...
OKAY [  2.610s]
writing 'system_a' 1/5...
OKAY [  2.235s]
sending sparse 'system_a' 2/5 (524284 KB)...
OKAY [  2.625s]
writing 'system_a' 2/5...
OKAY [  2.266s]
sending sparse 'system_a' 3/5 (524284 KB)...
OKAY [  2.469s]
writing 'system_a' 3/5...
OKAY [  2.266s]
sending sparse 'system_a' 4/5 (521176 KB)...
OKAY [  2.454s]
writing 'system_a' 4/5...
OKAY [  2.261s]
sending sparse 'system_a' 5/5 (167104 KB)...
OKAY [  0.797s]
writing 'system_a' 5/5...
OKAY [  0.734s]
finished. total time: 20.794s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash system_b system.img
target reported max download size of 536870912 bytes
erasing 'system_b'...
OKAY [  0.062s]
sending sparse 'system_b' 1/5 (524284 KB)...
OKAY [  2.469s]
writing 'system_b' 1/5...
OKAY [  2.294s]
sending sparse 'system_b' 2/5 (524284 KB)...
OKAY [  2.453s]
writing 'system_b' 2/5...
OKAY [  2.250s]
sending sparse 'system_b' 3/5 (524284 KB)...
OKAY [  2.453s]
writing 'system_b' 3/5...
OKAY [  2.250s]
sending sparse 'system_b' 4/5 (521176 KB)...
OKAY [  2.449s]
writing 'system_b' 4/5...
OKAY [  2.276s]
sending sparse 'system_b' 5/5 (167104 KB)...
OKAY [  0.781s]
writing 'system_b' 5/5...
OKAY [  0.734s]
finished. total time: 20.474s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash modem_a modem.img
target reported max download size of 536870912 bytes
sending 'modem_a' (60380 KB)...
OKAY [  0.231s]
writing 'modem_a'...
OKAY [  1.312s]
finished. total time: 1.543s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash modem_b modem.img
target reported max download size of 536870912 bytes
sending 'modem_b' (60380 KB)...
OKAY [  0.250s]
writing 'modem_b'...
OKAY [  1.328s]
finished. total time: 1.578s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash abl_a abl.img
target reported max download size of 536870912 bytes
sending 'abl_a' (540 KB)...
OKAY [ -0.000s]
writing 'abl_a'...
OKAY [  0.031s]
finished. total time: 0.031s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash --slot all abl.img
unknown partition 'abl.img'
error: cannot determine image filename for 'abl.img'

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe --slot all flash abl.img
unknown partition 'abl.img'
error: cannot determine image filename for 'abl.img'

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash abl_b abl.img
target reported max download size of 536870912 bytes
sending 'abl_b' (540 KB)...
OKAY [  0.016s]
writing 'abl_b'...
OKAY [  0.016s]
finished. total time: 0.031s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash aes_a aes.img
target reported max download size of 536870912 bytes
sending 'aes_a' (48 KB)...
OKAY [ -0.000s]
writing 'aes_a'...
OKAY [  0.016s]
finished. total time: 0.016s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash aes_b aes.img
target reported max download size of 536870912 bytes
sending 'aes_b' (48 KB)...
OKAY [  0.000s]
writing 'aes_b'...
OKAY [  0.016s]
finished. total time: 0.016s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash cmnlib_a cmnlib.img
target reported max download size of 536870912 bytes
sending 'cmnlib_a' (220 KB)...
OKAY [ -0.000s]
writing 'cmnlib_a'...
OKAY [  0.016s]
finished. total time: 0.016s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash cmnlib_b cmnlib.img
target reported max download size of 536870912 bytes
sending 'cmnlib_b' (220 KB)...
OKAY [ -0.000s]
writing 'cmnlib_b'...
OKAY [  0.016s]
finished. total time: 0.016s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash cmnlib64_a cmnlib64.img
target reported max download size of 536870912 bytes
sending 'cmnlib64_a' (288 KB)...
OKAY [  0.016s]
writing 'cmnlib64_a'...
OKAY [  0.016s]
finished. total time: 0.031s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash cmnlib64_b cmnlib64.img
target reported max download size of 536870912 bytes
sending 'cmnlib64_b' (288 KB)...
OKAY [ -0.000s]
writing 'cmnlib64_b'...
OKAY [  0.017s]
finished. total time: 0.017s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash devcfg_a devcfg.img
target reported max download size of 536870912 bytes
sending 'devcfg_a' (60 KB)...
OKAY [ -0.000s]
writing 'devcfg_a'...
OKAY [  0.016s]
finished. total time: 0.016s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash devcfg_b devcfg.img
target reported max download size of 536870912 bytes
sending 'devcfg_b' (60 KB)...
OKAY [  0.016s]
writing 'devcfg_b'...
OKAY [  0.013s]
finished. total time: 0.029s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash dtbo_a dtbo.img
target reported max download size of 536870912 bytes
sending 'dtbo_a' (8192 KB)...
OKAY [  0.037s]
writing 'dtbo_a'...
OKAY [  0.109s]
finished. total time: 0.146s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash dtbo_b dtbo.img
target reported max download size of 536870912 bytes
sending 'dtbo_b' (8192 KB)...
OKAY [  0.031s]
writing 'dtbo_b'...
OKAY [  0.141s]
finished. total time: 0.172s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash hyp_a hyp.img
target reported max download size of 536870912 bytes
sending 'hyp_a' (264 KB)...
OKAY [  0.000s]
writing 'hyp_a'...
OKAY [  0.020s]
finished. total time: 0.020s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash hyp_b hyp.img
target reported max download size of 536870912 bytes
sending 'hyp_b' (264 KB)...
OKAY [  0.014s]
writing 'hyp_b'...
OKAY [  0.000s]
finished. total time: 0.015s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash keymaster_a keymaster.img
target reported max download size of 536870912 bytes
sending 'keymaster_a' (308 KB)...
OKAY [  0.000s]
writing 'keymaster_a'...
OKAY [  0.026s]
finished. total time: 0.026s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash keymaster_b keymaster.img
target reported max download size of 536870912 bytes
sending 'keymaster_b' (308 KB)...
OKAY [  0.012s]
writing 'keymaster_b'...
OKAY [ -0.000s]
finished. total time: 0.012s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash laf_a laf.img
target reported max download size of 536870912 bytes
sending 'laf_a' (29800 KB)...
OKAY [  0.125s]
writing 'laf_a'...
OKAY [  0.406s]
finished. total time: 0.547s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash laf_b laf.img
target reported max download size of 536870912 bytes
sending 'laf_b' (29800 KB)...
OKAY [  0.110s]
writing 'laf_b'...
OKAY [  0.125s]
finished. total time: 0.250s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash pmic_a pmic.img
target reported max download size of 536870912 bytes
sending 'pmic_a' (52 KB)...
OKAY [ -0.000s]
writing 'pmic_a'...
OKAY [  0.016s]
finished. total time: 0.016s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash pmic_b pmic.img
target reported max download size of 536870912 bytes
sending 'pmic_b' (52 KB)...
OKAY [ -0.000s]
writing 'pmic_b'...
OKAY [  0.016s]
finished. total time: 0.016s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash rpm_a rpm.img
target reported max download size of 536870912 bytes
sending 'rpm_a' (232 KB)...
OKAY [  0.016s]
writing 'rpm_a'...
OKAY [  0.009s]
finished. total time: 0.024s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash rpm_b rpm.img
target reported max download size of 536870912 bytes
sending 'rpm_b' (232 KB)...
OKAY [ -0.000s]
writing 'rpm_b'...
OKAY [  0.000s]
finished. total time: 0.017s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash tz_a tz.img
target reported max download size of 536870912 bytes
sending 'tz_a' (1868 KB)...
OKAY [  0.016s]
writing 'tz_a'...
OKAY [  0.026s]
finished. total time: 0.045s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash tz_b tz.img
target reported max download size of 536870912 bytes
sending 'tz_b' (1868 KB)...
OKAY [  0.016s]
writing 'tz_b'...
OKAY [  0.016s]
finished. total time: 0.045s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash vbmeta_a vbmeta.img
target reported max download size of 536870912 bytes
sending 'vbmeta_a' (4 KB)...
OKAY [ -0.000s]
writing 'vbmeta_a'...
OKAY [  0.016s]
finished. total time: 0.016s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash vbmeta_b vbmeta.img
target reported max download size of 536870912 bytes
sending 'vbmeta_b' (4 KB)...
OKAY [  0.000s]
writing 'vbmeta_b'...
OKAY [  0.017s]
finished. total time: 0.020s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash xbl_a xbl.img
target reported max download size of 536870912 bytes
sending 'xbl_a' (2620 KB)...
OKAY [  0.016s]
writing 'xbl_a'...
OKAY [  0.016s]
finished. total time: 0.031s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flash xbl_b xbl.img
target reported max download size of 536870912 bytes
sending 'xbl_b' (2620 KB)...
OKAY [  0.016s]
writing 'xbl_b'...
OKAY [  0.016s]
finished. total time: 0.031s

C:\Program Files (x86)\Minimal ADB and Fastboot&gt;fastboot.exe flashing lock