test(build): Zuse's minted pair as a stick -- the acceptance boots and the sessions use it

mkdiskimage.sh --starship-from IDENT ART lays a minted pair out as a StarshipOS stick: an identity
partition holding IDENT's bytes and an Artemis partition holding ART's, each exactly its file's
size (Artemis's signature and fence are placed from the volume's size). kernel/Makefile: a
zusestick target, made fresh for every boot, is ZUSEDISK's default (ZUSE_PAIR names the pair);
STICK_PAIR puts the pair in the PC stick. qemu_session.py's Zuse drive is the pair as a stick.
check_images.sh checks both forms byte for byte against the pair (60 PASS).

On today's kernel all 23 sessions pass on the Zuse stick, and acceptance: amd64, aarch64,
riscv64 to [zuse@Hera] ok>, POST 538/538, dict_hash 0xfec8c47cfc6f437f; v4 suite and test-32
0 failures. The plan gains Task 5, screen=boot (ruled 2026-10-28).

Plan: docs/v4.0.0/plans/2026-10-27-stick-4-one-disk.md, Task 1 (R1 as recommended).

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

.claude/CLAUDE.md

@@ -344,8 +344,11 @@ second, less-structured log location.
 **The disks (Captain Bob, 2026-10-26, the identity gate):** with no identity thumbdrive the system
 is headless -- no prompt -- so every boot needs Zuse. `kernel/Makefile`'s `ARTDISK` and `ZUSEDISK`
 default to the minted Zuse pair, `disk/zuse-scratch/artemis.img` and `zuse-thumb-ident.img` (a
-pair: her genesis marker is on that Artemis disk; `disk/README.md`). Put both back as committed
-(`git checkout -- disk/zuse-scratch`) before each architecture. The prompt is `[zuse@Hera] ok> `.
+pair: her genesis marker is on that Artemis disk; `disk/README.md`). Since 2026-10-28 `ZUSEDISK`
+is that pair laid out as a stick (`make ... zusestick`, `build/<arch>/kernel/zusestick.img`, made
+fresh for every boot: identity and Artemis partitions on one USB disk, STICK.md §4); `ARTDISK`
+stays the pair's Artemis file. Put both back as committed (`git checkout -- disk/zuse-scratch`)
+before each architecture. The prompt is `[zuse@Hera] ok> `.
 
 Do not claim a change is accepted until all three architectures have booted, and their logs are
 present in `logs/`:

disk/README.md

@@ -160,6 +160,16 @@ carrying timestamp noise in git history.
   `thumbdrives/zuse-thumb-ident.img`, which stay blank (that call is Captain
   Bob's).
 
+  **As a stick (2026-10-28, `docs/v4.0.0/plans/2026-10-27-stick-4-one-disk.md`,
+  R1):** the QEMU boots no longer attach `zuse-thumb-ident.img` raw. `make -f
+  kernel/Makefile ARCH=<arch> zusestick` lays the pair out as a StarshipOS
+  stick (`build/<arch>/kernel/zusestick.img`: an identity partition holding
+  this identity image's bytes, an Artemis partition holding this Artemis
+  image's bytes, each exactly its file's size), fresh before every boot, and
+  that is `ZUSEDISK`'s default; `make boot_image TARGET=PC
+  STICK_PAIR=disk/zuse-scratch` puts the pair in the PC stick the same way.
+  The files here are unchanged. Increment 5 retires the pair.
+
 - **The StarshipOS stick and data stick are not here** (2026-10-27,
   `docs/v4.0.0/STICK.md` §4, §9): they are build output, made fresh by
   `make boot_image TARGET=PC` (`build/boards/pc/lithos-pc.img`: ESP, StarshipOS

docs/v4.0.0/plans/2026-10-27-stick-4-one-disk.md

@@ -310,3 +310,38 @@ drives), §5 items 1, 2 and 5, §9 (entropy, parity), §11 increment 4.
   - the seven GPT modes.
 - [ ] **Step 5:** Suite; full acceptance; commit `feat(kernel): Artemis and Zuse from one disk --
   the stick; virtio Artemis leaves v4` with the logs.
+
+### Task 5: `screen=boot` -- the console on the screen until login (added 2026-10-28)
+
+Captain Bob, 2026-10-28: "yes, add screen=boot at the end of increment 4" -- for the SER5 smoke
+test after Task 4, which has no serial port: today the v4 boot turns the screen's console mirror off
+after POST (`sk_v4_block_chain`, `console_fb_mirror(0)`), so a failure after POST shows a black
+screen.
+
+**Files:**
+- Modify: `kernel/include/starkernel/kernel_args.h` (`int screen_boot;` in `KernelArgs`, before
+  `raw`; check `boot_info_offsets.h` -- `args` is the last field it may name, `BootDisk` comes after)
+- Modify: `kernel/src/boot/cmdline.c` (`screen=boot`, with or without `--`, as `system=` is parsed;
+  the last one wins; any other `screen=` value is ignored)
+- Modify: `kernel/src/kernel_main.c` (`sk_v4_block_chain`: with `screen_boot`, the mirror stays on
+  and the line `Screen: the console stays on until login (screen=boot)`; without it, as today)
+- Modify: `scripts/qemu_session.py` (mode `screen_boot`)
+- Modify: `boards/BRINGUP.md` (the PC section: the smoke test's `starforth.cfg` is
+  `system=v4 screen=boot`, Secure Boot off)
+
+**Behaviour:**
+- Before the first login only. Login draws the console as today; a logout darkens the screen as
+  today (`screen=boot` is for watching a boot, not a way round the identity gate: the screen shows
+  what serial shows, and nothing can be typed without Zuse).
+- Default (no argument): unchanged -- `screen_dark_until_login` still passes.
+- v3 (`system=v3`): unchanged.
+
+- [ ] **Step 1: Failing test.** Mode `screen_boot` (amd64, `KERNEL_ARGS=screen=boot`, no drive):
+  the `Screen:` line; 30 s after POST the screen is not black (at least 500 lit pixels, as
+  `screen_console_after_login` counts); no `ok> `. Today: FAIL.
+- [ ] **Step 2:** Run: FAIL.
+- [ ] **Step 3:** Implement.
+- [ ] **Step 4:** `screen_boot` passes on amd64 and aarch64 (riscv64's ramfb too, if the mode's
+  screendump works there); `screen_dark_until_login`, `screen_dark_after_logout`, `zuse` pass.
+- [ ] **Step 5:** Suite; full acceptance; commit `feat(kernel): screen=boot keeps the console on the
+  screen until login -- for watching a PC boot` with the logs.

kernel/Makefile

@@ -162,7 +162,13 @@ XHCI_ARGS_SLOT4    := $(if $(strip $(XHCI_QEMU_ARGS)),$(XHCI_QEMU_ARGS),$(XHCI_D
 # xhci_poll_events() alone is purely hotplug-event-driven and would never
 # see a device present before controller reset. Override to "" (empty) to
 # boot without Zuse attached, e.g. `make -f kernel/Makefile qemu ZUSEDISK=`.
-ZUSEDISK           ?= disk/zuse-scratch/zuse-thumb-ident.img
+# Since 2026-10-27 (docs/v4.0.0/plans/2026-10-27-stick-4-one-disk.md, R1) the default is the
+# Zuse stick: the minted pair in ZUSE_PAIR laid out as a StarshipOS stick (`zusestick`, made
+# fresh for every boot), identity and Artemis partitions on one disk, as STICK.md 4 has them.
+ZUSE_PAIR          ?= disk/zuse-scratch
+ZUSESTICK_IMG       = $(BUILD_DIR)/zusestick.img
+ZUSEDISK           ?= $(ZUSESTICK_IMG)
+ZUSESTICK_DEP       = $(if $(filter $(ZUSESTICK_IMG),$(ZUSEDISK)),zusestick)
 # Precomputed (not inlined as $(if ...,...)) because the drive/device specs
 # below are comma-heavy and GNU make's $(if) function splits its own
 # arguments on every top-level comma -- inlining it silently truncated the
@@ -242,6 +248,9 @@ STICK_ESP_MIB      := 64
 STICK_IDENT_MIB    := 500
 DATASTICK_MIB      := 1536
 DATASTICK_IMG       = $(BUILD_DIR)/datastick.img
+# STICK_PAIR -- a minted pair (e.g. disk/zuse-scratch) whose identity and Artemis images become
+# the PC stick's partitions, byte for byte, instead of a blank identity and a fresh Artemis.
+STICK_PAIR         ?=
 
 # ==============================================================================
 # TOOLCHAIN
@@ -781,6 +790,12 @@ datastick: $(MKARTEMIS_BIN)
 	@bash scripts/mkdiskimage.sh --out $(DATASTICK_IMG) --table gpt --size-mib $(DATASTICK_MIB) \
 	    --label DATASTICK --starship $(STICK_IDENT_MIB) --mkartemis $(MKARTEMIS_BIN) --esp-mib 0
 
+# zusestick -- Zuse's minted pair as a stick, fresh every time it is made (the ZUSEDISK default).
+.PHONY: zusestick
+zusestick:
+	@bash scripts/mkdiskimage.sh --out $(ZUSESTICK_IMG) --table gpt --label ZUSESTICK --esp-mib 0 \
+	    --starship-from $(ZUSE_PAIR)/zuse-thumb-ident.img $(ZUSE_PAIR)/artemis.img
+
 # Generate capsule_generated.c from capsules/
 CAPSULE_SRCS := $(shell find $(CAPSULES_DIR) -type f ! -name '.*' 2>/dev/null)
 $(CAPSULE_GENERATED): $(MKCAPSULE_BIN) $(CAPSULE_SRCS)
@@ -1005,7 +1020,7 @@ QEMU_DISPLAY ?= gtk
 # above) to give real ports to Zuse plus every identity drive attached this way.
 QEMU_EXTRA ?=
 
-qemu: all $(DATASTICK_DEP)
+qemu: all $(DATASTICK_DEP) $(ZUSESTICK_DEP)
 ifeq ($(ARCH),amd64)
 	@echo "=== Building ISO (amd64) ==="
 	@mkdir -p $(BUILD_DIR)/iso
@@ -1370,7 +1385,7 @@ $(RPI5_NATIVE_IMG): $(RPI5_NATIVE_ELF)
 # everything else is the Pi 5 image. One QEMU, foreground, serial to
 # logs/<TS>/aarch64-rpi5/ (2026-10-14, FABRIC-3.md SXXXIX).
 .PHONY: rpi5-rehearsal
-rpi5-rehearsal:
+rpi5-rehearsal: $(ZUSESTICK_DEP)
 	@if [ "$(ARCH)" != "aarch64" ] || [ "$(RPI5_NATIVE_BASE)" != "0x40080000" ]; then \
 		echo "rpi5-rehearsal: ARCH=aarch64 RPI5_NATIVE_BASE=0x40080000"; exit 1; fi
 	@rm -f $(RPI5_NATIVE_ELF) $(RPI5_NATIVE_IMG)
@@ -1421,8 +1436,10 @@ boot_image: all $(if $(BOARD_STICK),$(MKARTEMIS_BIN))
 	@# stick (A6); KERNEL_ARGS after it, and a later system= wins.
 	@printf '%s\n' 'system=v4 $(KERNEL_ARGS)' > $(BOARD_OUT)/starforth.cfg
 	@bash scripts/mkdiskimage.sh --out $(BOARD_OUT)/$(BOARD_IMAGE) --table gpt \
-	    $(if $(BOARD_STICK),--size-mib $(STICK_IMAGE_MIB) --starship $(STICK_IDENT_MIB) \
-	        --mkartemis $(MKARTEMIS_BIN) --esp-mib $(STICK_ESP_MIB),--size-mib $(BOOT_IMAGE_SIZE_MIB)) \
+	    $(if $(BOARD_STICK),$(if $(STICK_PAIR),--esp-mib $(STICK_ESP_MIB) --starship-from \
+	        $(STICK_PAIR)/zuse-thumb-ident.img $(STICK_PAIR)/artemis.img,--size-mib $(STICK_IMAGE_MIB) \
+	        --starship $(STICK_IDENT_MIB) --mkartemis $(MKARTEMIS_BIN) --esp-mib $(STICK_ESP_MIB)), \
+	        --size-mib $(BOOT_IMAGE_SIZE_MIB)) \
 	    --label LITHOS \
 	    $(LOADER_EFI):/EFI/BOOT/$(EFI_BOOTNAME) \
 	    $(BOARD_OUT)/startup.nsh:/startup.nsh \