fix(v4): the kernel's fatal stops halt, interrupts off, instead of spinning (#177)

sk_v4_run's three stops -- "not started", "did not let go of POST's
blocks", "stopped on a fault" -- ended in for (;;) { }: a core spinning at
100%, the thing #151 removed from the prompt. Each now calls sk_v4_stop()
(kernel/src/v4/sk_v4_stop.c): interrupts off, then arch_halt() for ever. Each
still says why first. sk_v4_stop.c added to the loader's and the kernel's v4
sources.

kernel/tests/test_sk_v4_stop.c, with arch_halt and arch_disable_interrupts
faked (the halt jumps back out after three calls; an alarm fails a spin):
against the stop as it was -- "spun for 2 s without halting"; now -- 2
checks, 0 failures: halts in a loop, interrupts off before the first halt.
Built for amd64, aarch64 and riscv64. #177's "seen on the three
architectures": no boot reaches these stops, so it is shown on the host only.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017RzZgrf7V7Zk2iczBXDRbm

kernel/src/v4/sk_v4.c

@@ -26,6 +26,7 @@
 #include "starkernel/v4/sk_v4_mint.h"
 #include "starkernel/v4/sk_v4.h"
 #include "starkernel/v4/sk_v4_identity.h"
+#include "starkernel/v4/sk_v4_stop.h"
 #include "starkernel/kbd_input.h"
 #include "starkernel/console.h"
 #include "starkernel/arch.h"
@@ -159,7 +160,7 @@ void sk_v4_run(void (*chain)(void), const BootDisk *boot_disk)
     blk_subsys_init(sk_v4_post_blk_ram, sizeof(sk_v4_post_blk_ram));
     if (!v4_boot_run(&boot)) {
         console_println("StarForth v4: not started");
-        for (;;) { }
+        sk_v4_stop();                    /* #177: halts, not a 100% spin */
     }
     if (chain) {
         /* the blocks are other blocks now: what the node has in its two
@@ -167,7 +168,7 @@ void sk_v4_run(void (*chain)(void), const BootDisk *boot_disk)
         chain();
         if (v4_boot_line(&boot, "EMPTY-BUFFERS", 13) != V4_TEXT_COMPLETED) {
             console_println("StarForth v4: the node did not let go of POST's blocks");
-            for (;;) { }
+            sk_v4_stop();                    /* #177: halts, not a 100% spin */
         }
     }
     sk_v4_identity_boot(boot_disk);
@@ -230,7 +231,7 @@ void sk_v4_run(void (*chain)(void), const BootDisk *boot_disk)
         else if (how == V4_BOOT_LINE_REFUSED) console_puts("Message refused\n ERROR\n");      /* the node's wire is full: error 19's words */
         else if (how == V4_BOOT_LINE_STOPPED) {
             console_println("StarForth v4: the node stopped on a fault");
-            for (;;) { }
+            sk_v4_stop();                    /* #177: halts, not a 100% spin */
         }
     }
 }