[Treble-Enabled Device Development A/AB ROMS] jbbandos:
Thanks, the 3.2.1-GAGUGA works - despite being unable to decrypt /data, but that isn't an issue.

Now I need to find a working parted compiled for arm64, and make sense of the 66 (!!!) partitions. I'm guessing I'll need to enlarge system_a to 3.5GB (it's 2.7GB currently), move the preas, preavs, patch_a and reserved5 up, and reduce userdata.

fdisk -l /dev/block/mmcblk0
Found valid GPT with protective MBR; using GPT

Disk /dev/block/mmcblk0: 61071360 sectors, 1148M
Logical sector size: 512
Disk identifier (GUID): f9f21fff-a8d4-5f0e-9746-594869aec34e
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 61071359

Number Start (sector) End (sector) Size Code Name
1 1024 2047 512K 0700 frp
2 2048 6143 2048K 0700 persist
3 6144 16383 5120K 0700 reserved1
4 16384 17407 512K 0700 reserved6
5 17408 18431 512K 0700 vrl
6 18432 19455 512K 0700 vrl_backup
7 19456 36863 8704K 0700 modem_secure
8 36864 49151 6144K 0700 nvme
9 49152 180223 64.0M 0700 oeminfo
10 180224 245759 32.0M 0700 secure_storage
11 245760 311295 32.0M 0700 modem_om
12 311296 319487 4096K 0700 modemnvm_factory
13 319488 327679 4096K 0700 modemnvm_backup
14 327680 352255 12.0M 0700 modemnvm_img
15 352256 360447 4096K 0700 modemnvm_system
16 360448 524287 80.0M 0700 splash2
17 524288 786431 128M 0700 cache
18 786432 1048575 128M 0700 odm_a
19 1048576 1052671 2048K 0700 bootfail_info
20 1052672 1056767 2048K 0700 misc
21 1056768 1122303 32.0M 0700 reserved2
22 1122304 1130495 4096K 0700 hhee_a
23 1130496 1146879 8192K 0700 hisee_fs_a
24 1146880 1179647 16.0M 0700 dfx
25 1179648 1212415 16.0M 0700 rrecord
26 1212416 1212927 256K 0700 fw_lpm3_a
27 1212928 1220607 3840K 0700 reserved3_a
28 1220608 1228799 4096K 0700 hisee_img_a
29 1228800 1253375 12.0M 0700 fastboot_a
30 1253376 1261567 4096K 0700 vector_a
31 1261568 1265663 2048K 0700 isp_boot_a
32 1265664 1294335 14.0M 0700 isp_firmware_a
33 1294336 1318911 12.0M 0700 fw_hifi_a
34 1318912 1335295 8192K 0700 teeos_a
35 1335296 1384447 24.0M 0700 erecovery_kernel_a
36 1384448 1449983 32.0M 0700 erecovery_ramdisk_a
37 1449984 1482751 16.0M 0700 erecovery_vendor_a
38 1482752 1515519 16.0M 0700 sensorhub_a
39 1515520 1564671 24.0M 0700 kernel_a
40 1564672 1589247 12.0M 0700 eng_system_a
41 1589248 1654783 32.0M 0700 recovery_ramdisk_a
42 1654784 1687551 16.0M 0700 recovery_vendor_a
43 1687552 1716223 14.0M 0700 dts_a
44 1716224 1720319 2048K 0700 dto_a
45 1720320 1724415 2048K 0700 trustfirmware_a
46 1724416 1839103 56.0M 0700 modem_fw_a
47 1839104 1863679 12.0M 0700 eng_vendor_a
48 1863680 1916927 26.0M 0700 reserved4_a
49 1916928 1933311 8192K 0700 preload_a
50 1933312 1937407 2048K 0700 recovery_vbmeta_a
51 1937408 1941503 2048K 0700 erecovery_vbmeta_a
52 1941504 1949695 4096K 0700 vbmeta_a
53 1949696 2113535 80.0M 0700 modemnvm_update_a
54 2113536 2179071 32.0M 0700 reserved7
55 2179072 2244607 32.0M 0700 version_a
56 2244608 3850239 784M 0700 vendor_a
57 3850240 5341183 728M 0700 product_a
58 5341184 5390335 24.0M 0700 prets
59 5390336 5406719 8192K 0700 pretvs
60 5406720 5799935 192M 0700 cust_a
61 5799936 11452415 2760M 0700 system_a
62 11452416 13762559 1128M 0700 preas
63 13762560 13828095 32.0M 0700 preavs
64 13828096 14237695 200M 0700 patch_a
65 14237696 14499839 128M 0700 reserved5
66 14499840 61071359 22.2G 0700 userdata