[One (M9) Android Development] ZippyDan:
Thanks for that suggestion. I guess that was my problem but I have had a pretty ****ty experience trying to update the firmware...

I tried using fastboot and htc_fastboot and I kept getting one of these errors

fastboot flash zip 4.49.605.11_NoBoot_NoRecovery_firmware.zip
target reported max download size of 800000000 bytes
sending 'zip' (49430 KB)...
OKAY [ 3.700s]
writing 'zip'...
(bootloader) HOSD CL#669662
(bootloader) ERR [SD_UPDATE_ERR] Read zipped android_info fail!
(bootloader) ERR [SD_UPDATE_ERR] sddownload failed: 12
(bootloader) ERR Update zip file failed.
(bootloader) ERR ZIP ERROR, exit read zip loop
(bootloader) Update zip file OK
(bootloader) ERR ZIP ERROR CODE, 12
(bootloader) end@Done
FAILED (remote: 12 RU_ZIP_ERROR )
finished. total time: 4.823s

or

fastboot flash zip 4.49.605.11_NoBoot_NoRecovery_firmware.zip
target reported max download size of 800000000 bytes
sending 'zip' (49430 KB)...
OKAY [ 3.815s]
writing 'zip'...
(bootloader) HOSD CL#669662
(bootloader) Perform pre-update
(bootloader) start@12
(bootloader) ERR inflate fail, zerr=-3, total_out=183837
(bootloader) ERR zerr=-3, Z_STREAM_END=1, total_out=183837
(bootloader) aboot_signed.img@FAIL
(bootloader) adsp.img@BYPASS
(bootloader) bootlocker.img@BYPASS
(bootloader) ERR inflate fail, zerr=-3, total_out=185651
(bootloader) ERR zerr=-3, Z_STREAM_END=1, total_out=185651
(bootloader) hosd_signed.img@FAIL
(bootloader) hyp-8994-1.img@100%
(bootloader) ERR inflate fail, zerr=-5, total_out=32205
(bootloader) ERR zerr=-5, Z_STREAM_END=1, total_out=32205
(bootloader) hyp-8994-1.img@FAIL
(bootloader) pg2fs_ship_signkey.img@BYPASS
(bootloader) ERR inflate fail, zerr=-3, total_out=7480
(bootloader) ERR zerr=-3, Z_STREAM_END=1, total_out=7480
(bootloader) pmic-8994-1.img@FAIL
(bootloader) rfg_1.img@BYPASS
(bootloader) ERR inflate fail, zerr=-3, total_out=92547
(bootloader) ERR zerr=-3, Z_STREAM_END=1, total_out=92547
(bootloader) rpm-8994-1.img@FAIL
(bootloader) ERR inflate fail, zerr=-3, total_out=350201
(bootloader) ERR zerr=-3, Z_STREAM_END=1, total_out=350201
(bootloader) sbl1-8994-1.img@FAIL
(bootloader) ERR inflate fail, zerr=-3, total_out=11533
(bootloader) ERR zerr=-3, Z_STREAM_END=1, total_out=11533
(bootloader) tz-8994-1.img@FAIL
(bootloader) radio.img@BYPASS
(bootloader) ERR [SD_UPDATE_ERR] int do_update_zip_buf(int): unzip_and_f
(bootloader) lash_images fail, err 21
(bootloader) ERR [SD_UPDATE_ERR] sddownload failed: 21
(bootloader) ERR Update zip file failed.
(bootloader) Update zip file OK
(bootloader) ERR ZIP ERROR CODE, 21
(bootloader) end@Done
FAILED (remote: 21 RU_UNZIP_FAIL )
finished. total time: 5.084s

or

HTC_fastboot flash zip 4.49.605.11_NoBoot_NoRecovery_firmware.zip
sending 'zip'... (49430 KB) OKAY
sending time = 3.435 secs
writing 'zip'... (bootloader) HOSD CL#669662
(bootloader) Perform pre-update
(bootloader) start@12
(bootloader) ERR inflate fail, zerr=-3, total_out=333334
(bootloader) ERR zerr=-3, Z_STREAM_END=1, total_out=333334
(bootloader) aboot_signed.img@FAIL
(bootloader) adsp.img@BYPASS
(bootloader) bootlocker.img@BYPASS
(bootloader) ERR inflate fail, zerr=-3, total_out=84148
(bootloader) ERR zerr=-3, Z_STREAM_END=1, total_out=84148
(bootloader) hosd_signed.img@FAIL
(bootloader) hyp-8994-1.img@100%
(bootloader) pg2fs_ship_signkey.img@BYPASS
(bootloader) pmic-8994-1.img@100%
(bootloader) rfg_1.img@BYPASS
(bootloader) ERR inflate fail, zerr=-3, total_out=93280
(bootloader) ERR zerr=-3, Z_STREAM_END=1, total_out=93280
(bootloader) rpm-8994-1.img@FAIL
(bootloader) ERR inflate fail, zerr=-3, total_out=61293
(bootloader) ERR zerr=-3, Z_STREAM_END=1, total_out=61293
(bootloader) sbl1-8994-1.img@FAIL
(bootloader) ERR inflate fail, zerr=-3, total_out=58583
(bootloader) ERR zerr=-3, Z_STREAM_END=1, total_out=58583
(bootloader) tz-8994-1.img@FAIL
(bootloader) radio.img@BYPASS
(bootloader) ERR [SD_UPDATE_ERR] int do_update_zip_buf(int): unzip_and_f
(bootloader) lash_images fail, err 21
(bootloader) ERR [SD_UPDATE_ERR] sddownload failed: 21
(bootloader) ERR Update zip file failed.
(bootloader) Update zip file OK
(bootloader) ERR ZIP ERROR CODE, 21
(bootloader) end@Done
FAIL21 RU_UNZIP_FAIL
FAILED (remote: 21 RU_UNZIP_FAIL )
Execution time is 6(s)

So, anyway at the end I sent this command

fastboot reboot bootloader

It seems I misremembered the command because it should be

fastboot reboot-bootloader

But I thought maybe my version still worked (alternate syntax?) because I got this response:

fastboot reboot bootloader
rebooting into bootloader...
OKAY [ 0.004s]
finished. total time: 0.006s

Well I guess that must have been the wrong command because now the phone just completely turned off and now won't respond to anything. Is it bricked?

Did it actually write part of the firmware unsuccessfully and leave the phone in a nonbootable state? Weird if so, because I actually had already gone through this cycle before (of firmware update failure and rebooting) and had been able to reboot with no problems. I thought maybe my downloaded zip file was corrupt, so I tried downloading it again, but I still kept getting the same errors.