Clarify: home-blocks thumbdrives are not bound to any particular size

Captain Bob's correction. 64MB (disk/zuse.img, usb-thumbdrive-test.img)
was always just an arbitrary QEMU-test convenience size, never a
real-world constraint -- but the docs and script didn't say so
explicitly, and an earlier memory's "16GB reference size" phrasing
(already hedged as tentative) risked reading as a decided target.

Audited the actual format for hardcoded size assumptions: none found.
homeblocks_sig_t already carries its own metadata_devblocks field,
recording whatever size a real drive's partition actually is.

Changes: scripts/bleach_zuse_img.sh gains a --size-mb override (tested
both the override and the unchanged default); disk/README.md's
zuse.img entry and FABRIC-3.md both now state the point explicitly;
the memory file and its MEMORY.md index line corrected to match (the
GPT layout's design point is the *proportions* -- small metadata
partition, everything else block storage -- not any absolute size).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CXjAPTEKrgY2Mrk25KoLDn

FABRIC-3.md

@@ -301,6 +301,18 @@ decisions get added here, not to `FABRIC-2.md`. Follow the same discipline `FABR
   kernel code touched this step (host-side test tooling only), so no 3-arch acceptance boot
   needed — single live amd64 QMP-hotplug confirmation is the right verification tier.
 
+  **Correction (Captain Bob, 2026-08-26): drives are not bound to any particular size.**
+  64MB was only ever this fixture's arbitrary test-convenience size, matching
+  `usb-thumbdrive-test.img`'s existing BOT-driver-testing precedent — never a real-world
+  constraint. Audited for anywhere this might have implied otherwise: the actual format
+  (`homeblocks_sig_t`) already carries its own `metadata_devblocks` field and hardcodes no
+  size anywhere, confirmed clean. `scripts/bleach_zuse_img.sh` gained a `--size-mb` override
+  so this was never a hidden assumption baked into the tooling either. The earlier
+  `project_usb_thumbdrive_gpt_layout.md` memory's "16GB reference size" phrasing (already
+  hedged as tentative, but risked reading as a target) corrected to state the point
+  explicitly — the GPT layout's design point is the *proportions* (small metadata partition,
+  everything else block storage), not any absolute size.
+
   **Still open, not attempted:** the mint-then-pin boot-sequence fix itself, the `MINT` word,
   and the Zuse recovery path.
 

disk/README.md

@@ -85,18 +85,26 @@ carrying timestamp noise in git history.
 
 - `zuse.img` — 64MB raw image simulating the physical Zuse superuser
   thumbdrive for QEMU testing (FABRIC-3.md, Phase 8: `zuse.img` "bleach"
-  mechanism, added 2026-08-26). Blank (all zero) at creation — reads back
+  mechanism, added 2026-08-26). **64MB is only this fixture's size, not a
-  as `HOMEBLOCKS_SIG_BLANK` via `homeblocks_sig_check()`, confirmed live
+  constraint on real home-blocks thumbdrives** (Captain Bob, 2026-08-26) —
-  (`xhci: USB drive not recognized (blank or foreign media)`), simulating
+  the design is not bound to any particular drive size; `homeblocks_sig_t`'s
-  a genuine first boot for exercising the still-to-be-built one-time
+  own `metadata_devblocks` field records whatever size is actually observed
-  mint-Zuse flow. **"Bleach" it back to this pristine/unminted state with
+  on a real drive, nothing in the format hardcodes one. 64MB here is purely
-  `scripts/bleach_zuse_img.sh`** before each first-boot test run, rather
+  an arbitrary QEMU-test convenience (matching `usb-thumbdrive-test.img`'s
-  than hand-regenerating the file — same all-zero content either way, the
+  existing precedent for BOT driver testing scale); use
-  script just makes the reset a single documented, repeatable command.
+  `scripts/bleach_zuse_img.sh --size-mb N` for a different test size. Blank
-  Deliberately a flat/raw image, not GPT-partitioned, matching
+  (all zero) at creation — reads back as `HOMEBLOCKS_SIG_BLANK` via
-  `homeblocks_sig_check()`'s current call site (`repl.c`,
+  `homeblocks_sig_check()`, confirmed live (`xhci: USB drive not recognized
-  `sig_start_fblock=0`) — both will move to a real GPT-partition-relative
+  (blank or foreign media)`), simulating a genuine first boot for exercising
-  offset together once a GPT parser exists, not attempted ahead of that.
+  the still-to-be-built one-time mint-Zuse flow. **"Bleach" it back to this
+  pristine/unminted state with `scripts/bleach_zuse_img.sh`** before each
+  first-boot test run, rather than hand-regenerating the file — same
+  all-zero content either way, the script just makes the reset a single
+  documented, repeatable command. Deliberately a flat/raw image, not
+  GPT-partitioned, matching `homeblocks_sig_check()`'s current call site
+  (`repl.c`, `sig_start_fblock=0`) — both will move to a real
+  GPT-partition-relative offset together once a GPT parser exists, not
+  attempted ahead of that.
 
 **Convention, standing as of 2026-08-22: every virtual disk/thumb-drive image
 used for testing — Artemis persistence disks above, and USB Mass Storage

scripts/bleach_zuse_img.sh

@@ -1,5 +1,6 @@
 #!/bin/bash
-# bleach_zuse_img.sh - Reset disk/zuse.img back to pristine/unminted state.
+# bleach_zuse_img.sh - Reset disk/zuse.img (or any home-blocks test image)
+# back to pristine/unminted state.
 #
 # disk/zuse.img simulates the physical Zuse superuser thumbdrive for QEMU
 # testing (FABRIC-3.md, Phase 8 kickoff). "Bleaching" it means restoring the
@@ -8,21 +9,43 @@
 # be exercised repeatedly during development without hand-regenerating the
 # whole image each time.
 #
+# 64MB is only this script's default -- an arbitrary QEMU-test convenience
+# size (matching the existing usb-thumbdrive-test.img precedent for BOT
+# driver testing scale), not a constraint on real home-blocks thumbdrives.
+# The design is not bound to any particular drive size: homeblocks_sig_t's
+# own metadata_devblocks field records whatever size is actually observed,
+# nothing in the format or this repo hardcodes one. Override with --size-mb
+# for a different test size.
+#
 # Deliberately a flat/raw image, not GPT-partitioned, matching the same
 # simplifying assumption homeblocks_sig_check()'s current call site in
 # repl.c uses (sig_start_fblock=0) -- both will need to move to a real
 # GPT-partition-relative offset together, once a GPT parser exists. Not
 # invented ahead of that work here.
 #
-# Usage: scripts/bleach_zuse_img.sh [path]
+# Usage: scripts/bleach_zuse_img.sh [path] [--size-mb N]
-#   path  Optional override; defaults to disk/zuse.img relative to repo root.
+#   path        Optional override; defaults to disk/zuse.img relative to repo root.
+#   --size-mb N Optional override; defaults to 64 (arbitrary test convenience, see above).
 
 set -euo pipefail
 
 REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
-IMG="${1:-$REPO_ROOT/disk/zuse.img}"
+IMG="$REPO_ROOT/disk/zuse.img"
 SIZE_MB=64
 
+while [ $# -gt 0 ]; do
+    case "$1" in
+        --size-mb)
+            SIZE_MB="$2"
+            shift 2
+            ;;
+        *)
+            IMG="$1"
+            shift
+            ;;
+    esac
+done
+
 if [ -e "$IMG" ] && [ ! -f "$IMG" ]; then
     echo "bleach_zuse_img: refusing to overwrite non-regular-file '$IMG'" >&2
     exit 1