sidecar sequencer last seen in liveness heist

Sidecar/C 0XV2:913-0000006:010:BRM23230002 was just installed in the switch 0 position of the new dublin environment in Emeryville. This is my best recollection of the sequence of steps that lead to the issue:

• brought all four Gimlets and both Sidecars to A2 using pilot sp off
• brought both Scrimlets to A0 to get new host OS bits
• once rebooted into new host bits, I was watching some logs on the Scrimlets
• took both Sidecars to A0 using pilot sp on
• one Sidecar came up fine, but BRM23230002 did not!
• the fans on BRM23230002 have been running full tilt since the problem started

The Scrimlet for the busted Sidecar is Gimlet/C BRM42220026.

The SP for the Sidecar appears to be broadcasting and visible, but will not accept control plane agent commands. I was able to take a dump. I took another dump 17 minutes later and it seems like everything has come to rest waiting on the sequencer task:

 $ diff -u <(humility -d hubris.core.8 tasks ) <(humility -d hubris.core.9 tasks)
humility: attached to dump
humility: attached to dump
--- /dev/fd/63  Fri Oct 18 23:26:35 2024
+++ /dev/fd/62  Fri Oct 18 23:26:35 2024
@@ -1,28 +1,28 @@
-system time = 82544321
+system time = 83571110
 ID TASK                       GEN PRI STATE
- 0 jefe                         0   0 recv, notif: fault timer(T+79)
+ 0 jefe                         0   0 recv, notif: fault timer(T+90)
  1 sys                          0   1 recv, notif: exti-wildcard-irq(irq6/irq7/irq8/irq9/irq10/irq23/irq40)
  2 rng_driver                   0   6 recv
  3 update_server                0   3 recv
  4 auxflash                     0   3 recv
- 5 net                          0   5 recv, notif: eth-irq(irq61) wake-timer(T+48)
+ 5 net                          0   5 recv, notif: eth-irq(irq61) wake-timer(T+259)
  6 control_plane_agent          0   7 wait: send to sequencer/gen0
  7 sprot                        0   4 notif: rot-irq timer(T+992)
  8 udpecho                      0   6 notif: socket
- 9 udpbroadcast                 0   6 notif: bit31(T+100)
+ 9 udpbroadcast                 0   6 notif: bit31(T+152)
 10 monorail                     0   6 wait: send to sequencer/gen0
 11 i2c_driver                   0   2 recv
-12 hiffy                        0   5 notif: bit31(T+124)
+12 hiffy                        0   5 notif: bit31(T+176)
 13 sensor                       0   4 recv
 14 ecp5_mainboard               0   3 recv
 15 ecp5_front_io                0   3 recv
-16 transceivers                 0   6 recv, notif: socket timer(T+93)
+16 transceivers                 0   6 recv, notif: socket timer(T+4)
 17 packrat                      0   3 recv
-18 sequencer                    0   4 notif: bit31(T+1)
+18 sequencer                    0   4 notif: bit31(T+2)
 19 thermal                      0   5 wait: send to sequencer/gen0
 20 power                        0   6 wait: send to sequencer/gen0
 21 validate                     0   5 recv
-22 ignition                     0   5 recv, notif: timer(T+275)
+22 ignition                     0   5 recv, notif: timer(T+486)
 23 vpd                          0   3 recv
 24 dump_agent                   0   6 wait: reply from sprot/gen0
 25 idle                         0   8 RUNNING

Start with the two humility task dumps and compare the sequencer, control_plane_agent, monorail, thermal, and power tasks. Trace why the sequencer remains on its notification while other tasks wait for it; done means identifying the cause and validating that control-plane commands can proceed on the affected Sidecar.