feat(init): spawn service over IPC with per-client allowance refunded on child death; up to 4 death watchers; spawntest on test image

scripts/make-disk-image.sh

@@ -33,6 +33,8 @@ copy session-server "session.elf"
 # Only the test image: its presence makes init run the SMP self-test.
 if [ -n "${SMPTEST:-}" ]; then
     copy smptest    "smptest.elf"
+    copy spawntest  "spawntst.elf"
+    copy hello      "hello.elf"
 fi
 
 echo ""

scripts/test-qemu.sh

@@ -1,6 +1,7 @@
 #!/bin/bash
-# Boots IMAGE headless and waits for init's SMP self-test to report; the
-# machine halts itself when done. Exit 0 only on "SMPTEST PASS".
+# Boots IMAGE headless and waits for the self-test (init's SMP checks, then
+# spawntest) to report; the machine halts itself when done. Exit 0 only on
+# "SMPTEST PASS".
 set -uo pipefail
 
 IMAGE="${1:?usage: test-qemu.sh IMAGE}"
@@ -15,7 +16,7 @@ timeout ${QT:-120} qemu-system-riscv64 -machine virt -smp "${SMP}" -bios default
     -display none -serial "file:${LOG}" -monitor none
 status=$?
 
-grep -a "smptest:\|SMPTEST" "${LOG}"
+grep -a "smptest:\|spawntest:\|Hello\|SMPTEST" "${LOG}"
 if grep -aq "SMPTEST PASS" "${LOG}"; then
     echo "test-qemu: pass (${SMP} harts)"
     rm -f "${LOG}"