feat(boot): the loader tells the kernel its boot disk; system=v3 is refused on a stick

uefi.h: the UEFI device path and Block I/O protocols, a typed LocateDevicePath, and BootDisk
{gpt, is_stick, disk_guid[16]} appended to BootInfo after args (boot_info_offsets.h unchanged).
The loader, before ExitBootServices, cuts its image's device path at the partition's HardDrive
node, locates the whole disk's Block I/O (whole path consumed, not a logical partition, 512-byte
blocks), reads it as 1 KiB blocks through a loader-side blkio adapter, and runs the kernel's own
gpt_read: is it a StarshipOS stick (identity and Artemis partitions), and its DiskGUID
(gpt_disk_guid, new). No HardDrive node (an ISO/CD boot), no GPT, or any failure: not a stick.
Monolithic builds only (the non-monolithic loader does not link gpt.c, and does not build today:
kernel/src/vm/vm_core.c -- reported, not fixed).

The kernel prints 'Boot disk: a StarshipOS stick' or '... not a StarshipOS stick', and on a stick
system=v3 gives 'System: v3 is not on this stick -- StarForth v4' and boots v4.

Tests: stick_v3 (new), stick_boot and zuse x3 failed on the new lines before, pass after; v3_keys
still boots v3 off a stick. Acceptance: amd64, aarch64, riscv64 to [zuse@Hera] ok>, POST 538/538,
dict_hash 0xfec8c47cfc6f437f; v4 suite and test-32 0 failures.

Plan: docs/v4.0.0/plans/2026-10-27-stick-4-one-disk.md, Task 3.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

scripts/qemu_session.py

@@ -49,6 +49,8 @@ the stick's, plan 2026-10-26-stick-1-screen-and-keyboard.md):
                blank identity partition attached (500 MiB, not the 2 GiB disk); headless
   datastick    --make "DATASTICK=1 ...": the data stick over USB beside Zuse's drive; Zuse
                still logs in; the data stick's identity partition attached
+  stick_v3     --target qemu-stick, system=v3 in the stick's starforth.cfg: "Boot disk: a StarshipOS
+               stick", the refusal, then v4's POST; no v3 (plan 2026-10-27-stick-4-one-disk.md, Task 3)
   entropy      after "System: StarForth v4", the entropy backend -- rdrand on amd64 (qemu and
                --target qemu-stick), virtio-rng on aarch64 and riscv64 -- then "entropy: ready";
                on the qemu target, [zuse@Hera] ok> (plan 2026-10-27-stick-4-one-disk.md, Task 2)
@@ -74,7 +76,7 @@ NO_ZUSE_MODES = {"gpt_zuse", "gpt_hotplug", "gpt_foreign", "gpt_bad_crc", "gpt_b
                  "gpt_read_error", "headless", "hotplug", "midpull", "waitpull", "typeahead", "emergency",
                  "alttab_after_logout", "alttab_before_pull", "emergency_pull",
                  "screen_dark_until_login", "screen_console_after_login", "screen_dark_after_logout",
-                 "kbd_typeahead", "stick_boot"}
+                 "kbd_typeahead", "stick_boot", "stick_v3"}
 label = a.label or f"{a.mode}-{a.arch}"
 work = os.path.join(ROOT, "build", "qemu-session", label)
 shutil.rmtree(work, ignore_errors=True)
@@ -96,7 +98,7 @@ attach_zuse = not (a.no_zuse or a.mode in NO_ZUSE_MODES)
 zdrive = ident if a.mode == "v3_keys" else zimg
 make_args = ["make", "-f", "kernel/Makefile", f"ARCH={a.arch}", "clean", a.target, f"ARTDISK={art}",
              f"ZUSEDISK={zdrive if attach_zuse else ''}"] + shlex.split(a.make)
-if a.mode == "v3_keys":
+if a.mode in ("v3_keys", "stick_v3"):
     make_args.append("KERNEL_ARGS=system=v3")
 start = time.time()
 make_log = open(os.path.join(work, "make.txt"), "w")
@@ -297,6 +299,8 @@ if m == "headless":
     check("no ok> for 60 s after POST", not wait_for(ANYPROMPT, 60))
 
 elif m == "zuse":
+    check("Boot disk: not a StarshipOS stick (an ISO or ESP boot)",
+          re.search(r"Boot disk: not a StarshipOS stick", text()) is not None)
     check("Zuse: identity confirmed", wait_for(r"Zuse: identity confirmed from attached thumbdrive", 120))
     check("[zuse@Hera] ok>", wait_for(PROMPT, 60))
     n = count(PROMPT)
@@ -312,6 +316,7 @@ elif m in ("stick_boot", "datastick"):
         users = [int(u) for u in re.findall(r"blk: disk .*?\((\d+) use", text())]
         return any(300000 < u < 512000 for u in users), users
     if m == "stick_boot":
+        check("Boot disk: a StarshipOS stick", re.search(r"Boot disk: a StarshipOS stick", text()) is not None)
         check("System: StarForth v4", re.search(r"System: StarForth v4", text()) is not None)
         time.sleep(20)
         found, users = ident_attached()
@@ -329,6 +334,15 @@ elif m in ("stick_boot", "datastick"):
         check(f"the data stick's identity partition attached (user blocks {users})", found)
     check("no fault", count(r"EXCEPTION|PANIC|panic") == 0)
 
+elif m == "stick_v3":
+    t = text()
+    check("Boot disk: a StarshipOS stick", re.search(r"Boot disk: a StarshipOS stick", t) is not None)
+    check("System: v3 is not on this stick -- StarForth v4",
+          re.search(r"System: v3 is not on this stick -- StarForth v4", t) is not None)
+    check("v4's POST (PARITY:V4_POST)", re.search(r"PARITY:V4_POST tests=\d+ pass=\d+ fail=0", t) is not None)
+    check("no System: StarForth v3", re.search(r"System: StarForth v3", t) is None)
+    check("no fault", count(r"EXCEPTION|PANIC|panic") == 0)
+
 elif m == "entropy":
     want = "rdrand" if a.arch == "amd64" else "virtio-rng"
     wait_for(r"entropy: (ready|not available)|Zuse:|ok> ", 120)     # the block chain runs after POST