DF-5641 — decisive runtime observations (audit guest, single run, unedited values)

[1] hinted boot installed (loader.conf.local):
hint.acpi.0.disabled="1"
hint.atkbdc.0.at="isa"
hint.atkbdc.0.port="0x60"
hint.atkbdc.0.irq="1"
hint.psm.0.at="atkbdc0"
hint.psm.0.irq="12"

[2] after reboot — device tree (devinfo.hinted.txt, full):
nexus0
  ram0
  legacy0
    pcib0
      pci0
        hostb0
        isab0
          isa0
            atkbdc0          <- atkbdc on the ISA bus (isa child, valid ivars)
              atkbd0
              psm0           <- ISA GRANDCHILD: ivars are atkbdc_device_t, NOT isa_device
            vga0
            sio0
            orm0
        ...
(no acpi0 — hint.acpi.0.disabled honored, sys/dev/acpica/acpi.c:420)

[3] dmesg (dmesg.hinted.txt):
atkbdc0: <Keyboard controller (i8042)> at port 0x60,0x64 irq 1 on isa0
atkbd0: <AT Keyboard> irq 1 on atkbdc0
psm0: <PS/2 Mouse> irq 12 on atkbdc0
interrupt uses mplock: psm0
psm0: model IntelliMouse Explorer, device ID 4

[4] interrupt registration (env.txt) — proves the alloc chain through
    isa_alloc_resource(passthrough=1, type-confused rl) COMPLETED:
$ vmstat -i | grep -E "psm0|atkbd0"
psm0        0   0
atkbd0      0   0

[5] chain executed at psm.c:2014 -> subr_bus.c:3302-3308 BUS_ALLOC_RESOURCE
    -> atkbdc_isa.c:83 bus_generic_alloc_resource -> isa.c:76 isa_alloc_resource
    (isa.c:87 DEVTOISA(psm0) casts atkbdc_device_t* -> struct isa_device*)
    -> isa.c:122 resource_list_alloc -> subr_bus.c:2683 early forward (rl NEVER
    dereferenced) -> isab/pci/nexus -> IRQ 12 allocated -> handler registered.
    Guest alive, no panic, ssh responsive throughout.

[6] restoration:
$ truncate -s0 /boot/loader.conf.local; shutdown -r now
$ devinfo | grep -c acpi0
1
atkbdc0: <Keyboard controller (i8042)> port 0x64,0x60 irq 1 on acpi0   <- baseline restored