packaging/windows: fix BTRFS+QEMU boot-loop, document what's confirmed

Real issue hit on a real run: dockur/windows warns about BTRFS storage
but it's not idle -- on this host it boot-looped Windows Setup for
hours (same log lines repeating forever, disk barely growing), a known
bad combination for QEMU disk images on a copy-on-write filesystem.
build_windows.sh now disables COW on storage/ itself (chattr +C,
harmless no-op on non-btrfs or an already-populated dir from a prior
run). README updated to reflect both real fixes now confirmed needed
on this host (this one, plus the earlier SELinux :Z mount fix) instead
of the original "written but never run" status.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

packaging/windows/README.md

@@ -6,12 +6,28 @@ machine and no GitHub, by booting a real Windows VM inside a container
 hood, no license key needed for the eval install it fetches automatically)
 and driving the whole build over a shared folder.
 
-**Status: written, not yet run against a real boot.** Everything here
-follows dockur/windows's and WiX's documented mechanics, but there's no
-KVM/Windows available in the environment this was authored in to actually
-exercise it end to end. Treat the first run as a debugging session, not a
-push-button success — watch it happen at http://localhost:8006 (dockur's
-noVNC viewer) so you can see where it's stuck if it stalls.
+**Status: has actually been run.** Two real environment issues hit and
+fixed so far (both already applied in this directory, see "Confirmed
+issues hit" below); Windows install itself was still in progress as of
+last check. `oem/install.bat` onward (MSYS2/GTK4/WiX provisioning, the
+actual .msi packaging) has NOT been reached/exercised yet — treat that
+part as still a debugging session, not a push-button success. Watch it
+happen at http://localhost:8006 (dockur's noVNC viewer) if it stalls.
+
+## Confirmed issues hit (on Fedora + BTRFS)
+
+- **SELinux blocks the bind mounts** ("Storage folder (/storage) is not
+  writeable!") — fixed with `:Z` on every volume in `docker-compose.yml`.
+  Harmless no-op on a host without SELinux.
+- **BTRFS + QEMU disk images boot-loop Windows Setup for hours** with no
+  error, just the same boot-manager log lines repeating forever and the
+  disk barely growing — dockur/windows warns about this itself
+  ("you are using the BTRFS filesystem for /storage, this might
+  introduce issues with Windows Setup!"), and on this host it wasn't
+  idle chatter. Fixed by disabling copy-on-write on `storage/` before
+  the VM ever writes to it (`chattr +C`, only affects files created
+  after it's set, so it needs an empty directory) — `build_windows.sh`
+  now does this itself on every run. No-op on a non-btrfs filesystem.
 
 ## How it fits together
 

packaging/windows/build_windows.sh

@@ -30,6 +30,17 @@ fi
 command -v docker >/dev/null 2>&1 || { echo "docker not found." >&2; exit 1; }
 
 mkdir -p storage oem shared/src shared/dist "$OUT_DIR"
+# dockur/windows itself warns about this ("you are using the BTRFS
+# filesystem for /storage, this might introduce issues with Windows
+# Setup!") and it's not idle: confirmed on this host as a genuine
+# multi-hour Windows Setup boot-loop (repeating the same boot-manager
+# log lines forever, disk barely growing) -- QEMU disk images on a
+# copy-on-write filesystem are a known bad combination. +C only takes
+# effect for files created AFTER it's set on an empty directory, so
+# this only helps on a fresh/emptied storage/; it's a no-op (harmless,
+# chattr just errors quietly) on a non-btrfs filesystem or an
+# already-populated storage/ from a previous run.
+chattr +C storage 2>/dev/null || true
 
 echo "==> starting the Windows build VM (docker compose up -d)"
 docker compose up -d