chore(deploy): drop fuse-overlayfs apt dep + one-shot migrate upper/work

Drop fuse-overlayfs / fuse3 from the apt/dnf install line — the new
mount path is kernel overlayfs via the left4me-overlay helper, no
fuse userspace needed.

Add a one-shot migration block gated by /var/lib/left4me/.kernel-overlay-migrated
that runs before daemon-reload: stop gameservers + web service, force-
unmount any leftover fuse or overlay mounts under runtime/, then wipe
and recreate empty upper/ and work/ for every instance. fuse-overlayfs
running as a non-root user used user.fuseoverlayfs.* xattrs that kernel
overlayfs ignores, so a pre-existing upper/ from the fuse era would
resurrect "deleted" files.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

deploy/deploy-test-server.sh

@@ -79,9 +79,9 @@ fi
 
 if command -v apt-get >/dev/null 2>&1; then
     $sudo_cmd apt-get update
-    $sudo_cmd apt-get install -y python3 python3-venv python3-pip curl ca-certificates tar gzip fuse-overlayfs fuse3 sudo
+    $sudo_cmd apt-get install -y python3 python3-venv python3-pip curl ca-certificates tar gzip util-linux sudo
 elif command -v dnf >/dev/null 2>&1; then
-    $sudo_cmd dnf install -y python3 python3-pip curl ca-certificates tar gzip fuse-overlayfs fuse3 sudo
+    $sudo_cmd dnf install -y python3 python3-pip curl ca-certificates tar gzip util-linux sudo
 else
     printf 'Unsupported package manager: expected apt-get or dnf\n' >&2
     exit 1
@@ -178,6 +178,22 @@ if [ -f "$remote_tmp/admin_username" ] && [ -f "$remote_tmp/admin_password" ]; t
     fi
 fi
 
+# One-shot migration: fuse-overlayfs running as the left4me user used
+# user.fuseoverlayfs.* xattrs for whiteouts and opaque-dir markers; kernel
+# overlayfs ignores those entirely, so a pre-existing upper/ from the fuse
+# era would resurrect "deleted" files. Wipe upper/ and work/ for every
+# instance once, gated by a sentinel file so reruns are no-ops.
+overlay_sentinel=/var/lib/left4me/.kernel-overlay-migrated
+if [ ! -e "$overlay_sentinel" ]; then
+    $sudo_cmd sh -c "systemctl stop 'left4me-server@*.service' 2>/dev/null || true"
+    $sudo_cmd systemctl stop left4me-web.service 2>/dev/null || true
+    $sudo_cmd sh -c "findmnt -t fuse.fuse-overlayfs -o TARGET --noheadings 2>/dev/null | xargs -r -n1 umount -l 2>/dev/null || true"
+    $sudo_cmd sh -c "findmnt -t overlay -o TARGET --noheadings 2>/dev/null | grep '/var/lib/left4me/runtime/' | xargs -r -n1 umount -l 2>/dev/null || true"
+    $sudo_cmd sh -c 'for d in /var/lib/left4me/runtime/*/; do [ -d "$d" ] || continue; rm -rf "$d/upper" "$d/work"; mkdir -p "$d/upper" "$d/work"; chown left4me:left4me "$d/upper" "$d/work"; done'
+    $sudo_cmd touch "$overlay_sentinel"
+    $sudo_cmd chown left4me:left4me "$overlay_sentinel"
+fi
+
 $sudo_cmd systemctl daemon-reload
 $sudo_cmd systemctl enable --now left4me-web.service
 $sudo_cmd systemctl restart left4me-web.service

deploy/tests/test_deploy_artifacts.py

@@ -179,6 +179,30 @@ def test_deploy_script_installs_overlay_helper_with_executable_mode():
     assert "chmod 0755" in script and "left4me-overlay" in script
 
 
+def test_deploy_script_does_not_install_fuse_overlayfs_apt_dep():
+    # fuse-overlayfs / fuse3 were the previous mount engine; kernel overlayfs
+    # replaces them. Comments in the migration block may legitimately mention
+    # the names, so scope this to the actual apt-get / dnf install lines.
+    install_lines = [
+        line for line in DEPLOY_SCRIPT.read_text().splitlines()
+        if ("apt-get install" in line or "dnf install" in line)
+    ]
+    assert install_lines, "expected at least one apt/dnf install line"
+    for line in install_lines:
+        assert "fuse-overlayfs" not in line, line
+        assert "fuse3" not in line, line
+
+
+def test_deploy_script_runs_one_shot_kernel_overlay_migration():
+    script = DEPLOY_SCRIPT.read_text()
+    assert "/var/lib/left4me/.kernel-overlay-migrated" in script
+    # Migration should stop services + force-unmount stale mounts + wipe upper/work
+    assert "systemctl stop 'left4me-server@" in script
+    assert "systemctl stop left4me-web.service" in script
+    assert "findmnt -t overlay" in script
+    assert "/runtime/" in script and "rm -rf" in script and 'upper"' in script and 'work"' in script
+
+
 def test_env_templates_contain_required_defaults():
     host_env = HOST_ENV.read_text()
     assert "Deployment units use fixed /var/lib/left4me paths" in host_env