diff --git a/.github/workflows/e2e.yml b/.github/workflows/e2e.yml
index de39277..089ab5c 100644
--- a/.github/workflows/e2e.yml
+++ b/.github/workflows/e2e.yml
@@ -3,9 +3,10 @@
 #
 #   artifacts  this commit's release assets, built by deploy/build-release-artifacts.sh the
 #              way release.yml builds a tag's (amd64 only, the runners' architecture)
-#   install    a full install from those assets, the way a release installs, then the same
-#              assets again (a rerun must converge without restarting what did not change,
-#              importing or uploading an image again, or touching Docker)
+#   install    a full install from those assets, the way a release installs, on a host with
+#              ufw enabled, then the same assets again (a rerun must converge without
+#              restarting what did not change, importing or uploading an image again, or
+#              touching Docker)
 #   readme     the README's one-line install as a new host runs it today: this commit's
 #              installer on its default channel, which installs the newest published
 #              release's binary, images and plugin from that release's assets; skipped until
@@ -98,12 +99,21 @@ jobs:
       # whether bootstrap reached for it. From FELIS_ARTIFACT_DIR every image and the plugin
       # come out of the assets, so it must not have. (`! grep` is spelled `if grep ... exit 1`
       # below because bash -e ignores a failing `!` command.)
+      # ufw, enabled on many Ubuntu hosts, drops every inbound packet no rule admits, the
+      # pods' traffic to the API server among them; the runner ships it disabled. The
+      # runner's own traffic is outbound, which ufw lets through.
+      - name: Enable ufw
+        run: sudo ufw --force enable
+
       - name: Install
         run: sudo FELIS_ARTIFACT_DIR="$GITHUB_WORKSPACE/dist" FELIS_INSTALL_MODE=full bash deploy/bootstrap.sh 2>&1 | tee install.log
 
       - name: Check the install
         run: |
           sudo bash deploy/e2e_check.sh install
+          for tag in felis-k3s-pods felis-k3s-services felis-panel felis-proxy; do
+            sudo ufw status | grep -qE "# ${tag} *$"
+          done
           if grep -E 'docker already installed|installing docker|docker running' install.log; then exit 1; fi
           for role in felis limbo lobby paper; do
             grep -q "felis/${role}:[^ ]* is the release's" install.log
diff --git a/deploy/bootstrap.sh b/deploy/bootstrap.sh
index 2175f29..0347fde 100644
--- a/deploy/bootstrap.sh
+++ b/deploy/bootstrap.sh
@@ -1786,10 +1786,31 @@ stop_docker() {
 # 4. k3s — single node, trimmed for RAM. NetworkPolicy stays ENABLED on purpose:
 #    Felis's minecraft fence (default-deny + allow-rcon/allow-game) is a core
 #    security claim, so we must NOT pass --disable-network-policy.
-#    On SUSE-family hosts firewalld ships active by default; open the required
-#    rules rather than disabling the firewall.
+#    On SUSE-family hosts firewalld ships active by default, and Ubuntu and Debian
+#    hosts often enable ufw; open the required rules rather than disabling either.
 # ---------------------------------------------------------------------------
+
+# ufw_active reports whether ufw is enabled. Enabled, it drops every inbound packet no rule
+# admits, the pods' traffic to the API server among them, so an install that left it alone
+# waited out its first rollout and died with "did not complete". ufw translates its status
+# line, hence the C locale.
+ufw_active() {
+  command -v ufw >/dev/null 2>&1 || return 1
+  [ "$(LC_ALL=C ufw status 2>/dev/null | head -n 1)" = "Status: active" ]
+}
+
+# configure_k3s_firewall opens what k3s needs. For ufw that is what k3s's documentation asks:
+# the pod and service ranges, plus the panel's NodePort as firewalld gets it. The API
+# server's 6443 stays closed to the network, since pods reach it from POD_CIDR. Each ufw rule
+# carries a felis- comment, which is how deploy/uninstall.sh finds it again; `ufw allow`
+# skips a rule it already has, so a rerun adds nothing.
 configure_k3s_firewall() {
+  if ufw_active; then
+    log "configuring ufw for k3s"
+    ufw allow from "$POD_CIDR" comment felis-k3s-pods >/dev/null
+    ufw allow from "$SERVICE_CIDR" comment felis-k3s-services >/dev/null
+    ufw allow "${FELIS_PANEL_NODEPORT}/tcp" comment felis-panel >/dev/null
+  fi
   command -v firewall-cmd >/dev/null 2>&1 || return 0
   systemctl is-active --quiet firewalld || return 0
 
@@ -3773,6 +3794,10 @@ velocity_fingerprint() {
 }
 
 configure_velocity_firewall() {
+  if ufw_active; then
+    log "opening ufw port ${FELIS_GAME_PORT}/tcp for the Minecraft proxy"
+    ufw allow "${FELIS_GAME_PORT}/tcp" comment felis-proxy >/dev/null
+  fi
   command -v firewall-cmd >/dev/null 2>&1 || return 0
   systemctl is-active --quiet firewalld || return 0
   log "opening firewalld port ${FELIS_GAME_PORT}/tcp for the Minecraft proxy"
@@ -5483,9 +5508,17 @@ configure_nano_firewall() {
     ok "nano listens on ${FELIS_NANO_LISTEN} (loopback); no firewall port opened"
     return 0
   fi
+  local port="${FELIS_NANO_LISTEN##*:}" family=ipv4
+  if ufw_active; then
+    if [ -n "$FELIS_NANO_PROXY_CIDR" ]; then
+      log "opening ufw port ${port}/tcp to ${FELIS_NANO_PROXY_CIDR} only"
+      ufw allow proto tcp from "$FELIS_NANO_PROXY_CIDR" to any port "$port" comment felis-nano >/dev/null
+    else
+      warn "no FELIS_NANO_PROXY_CIDR, so ufw keeps ${port}/tcp closed; the summary shows how to admit your proxy"
+    fi
+  fi
   command -v firewall-cmd >/dev/null 2>&1 || return 0
   systemctl is-active --quiet firewalld || return 0
-  local port="${FELIS_NANO_LISTEN##*:}" family=ipv4
   # hasJoined takes no token, so the port is opened to the proxy alone. Earlier installers
   # opened it to every source, and a re-run must not leave that behind. A rule for a previous
   # FELIS_NANO_PROXY_CIDR is not tracked; it stays until removed by hand.
@@ -5560,16 +5593,17 @@ summary_nano() {
     log "Proxy on another machine? Re-run with the address on the sudo line (sudo drops"
     log "exported variables):"
     log "    curl -fsSL <raw-url>/deploy/bootstrap.sh | sudo FELIS_NANO_LISTEN=<private-ip>:${port} FELIS_NANO_PROXY_CIDR=<proxy-ip>/32 bash"
-    log "firewalld then admits ${port}/tcp ONLY from that proxy — hasJoined takes no auth token,"
+    log "firewalld or ufw then admits ${port}/tcp ONLY from that proxy — hasJoined takes no auth token,"
     log "so an internet-facing one is a free auth relay burning your Mojang egress IP."
   elif [ -n "$FELIS_NANO_PROXY_CIDR" ]; then
-    log "Bound to ${FELIS_NANO_LISTEN}. firewalld, where it runs, admits ${port}/tcp only from"
+    log "Bound to ${FELIS_NANO_LISTEN}. firewalld or ufw, where it runs, admits ${port}/tcp only from"
     log "${FELIS_NANO_PROXY_CIDR}; any other firewall in front of this host must do the same."
   else
     log "WARNING: bound to ${FELIS_NANO_LISTEN} with no FELIS_NANO_PROXY_CIDR. hasJoined takes no auth"
     log "token, so admit ${port}/tcp from your proxy alone, or anyone can relay their logins"
-    log "through you. firewalld, where it runs, keeps the port closed until you add:"
+    log "through you. firewalld or ufw, where it runs, keeps the port closed until you add one of:"
     log "    firewall-cmd --permanent --add-rich-rule='rule family=\"ipv4\" source address=\"<proxy-ip>/32\" port port=\"${port}\" protocol=\"tcp\" accept' && firewall-cmd --reload"
+    log "    ufw allow proto tcp from <proxy-ip>/32 to any port ${port} comment felis-nano"
   fi
   log "Then edit ${STATE_DIR}/felis.toml to add your [[auth_source]] roots and run:"
   log "    sudo systemctl restart felis-nano"
diff --git a/deploy/bootstrap_test.sh b/deploy/bootstrap_test.sh
index e7684a0..97fe94e 100644
--- a/deploy/bootstrap_test.sh
+++ b/deploy/bootstrap_test.sh
@@ -585,8 +585,24 @@ fblock="$(awk '/^configure_nano_firewall\(\) \{/,/^}/' "$BS")"
 [ "$(printf '%s\n' "$fblock" | wc -l)" -lt 40 ] \
   || { echo "FAIL: the extracted block is not the function -- did its closing brace move?"; exit 1; }
 
-run_fw() { # listen proxy-cidr port-already-open(0|1)
-  FELIS_NANO_LISTEN="$1" FELIS_NANO_PROXY_CIDR="$2" OPEN="$3" bash -c '
+# ufw_stub is ufw for a run: UFW=active or inactive, its status line translated outside the
+# C locale as ufw translates it; every other call is printed to stderr, which the installer
+# leaves alone when it silences ufw's "Rule added".
+ufw_stub='
+    ufw() {
+      case "$*" in
+        status)
+          if [ "${UFW:-inactive}" != active ]; then echo "Status: inactive"
+          elif [ "${LC_ALL:-}" = C ]; then echo "Status: active"
+          else echo "状态：激活"; fi ;;
+        *) printf "UFW: %s\n" "$*" >&2 ;;
+      esac
+    }'
+ublock="$(awk '/^ufw_active\(\) \{/,/^}/' "$BS")"
+[ -n "$ublock" ] || { echo "FAIL: no ufw_active found in $BS"; exit 1; }
+
+run_fw() { # listen proxy-cidr port-already-open(0|1) [ufw-state]
+  FELIS_NANO_LISTEN="$1" FELIS_NANO_PROXY_CIDR="$2" OPEN="$3" UFW="${4:-inactive}" bash -c '
     ok() { printf "OK: %s\n" "$*"; }
     log() { printf "LOG: %s\n" "$*"; }
     warn() { printf "WARN: %s\n" "$*"; }
@@ -595,6 +611,8 @@ run_fw() { # listen proxy-cidr port-already-open(0|1)
       case "$*" in *--query-port=*) [ "$OPEN" = 1 ]; return ;; esac
       printf "FW: %s\n" "$*"
     }
+    '"$ufw_stub"'
+    '"$ublock"'
     '"$kblock"'
     '"$fblock"'
     configure_nano_firewall' 2>&1
@@ -627,6 +645,61 @@ case "$(run_fw 127.0.0.1:8081 10.0.0.7/32 1)" in
   *) echo "PASS a loopback bind leaves firewalld alone" ;;
 esac
 
+# ufw, enabled on many Ubuntu and Debian hosts, drops what no rule admits.
+out="$(run_fw 0.0.0.0:8081 10.0.0.7/32 0 active)"
+expect "ufw admits the nano port from the proxy CIDR alone" \
+  "UFW: allow proto tcp from 10.0.0.7/32 to any port 8081 comment felis-nano" "$out"
+out="$(run_fw 0.0.0.0:8081 '' 0 active)"
+expect "no proxy CIDR says ufw keeps the port closed" "WARN: no FELIS_NANO_PROXY_CIDR, so ufw keeps 8081/tcp closed" "$out"
+case "$out" in
+  *"UFW: allow"*) echo "FAIL no proxy CIDR must add no ufw rule:"; echo "$out"; fails=$((fails + 1)) ;;
+  *) echo "PASS no proxy CIDR adds no ufw rule" ;;
+esac
+for args in "127.0.0.1:8081 10.0.0.7/32 0 active" "0.0.0.0:8081 10.0.0.7/32 0 inactive"; do
+  # shellcheck disable=SC2086 # the words are the arguments
+  case "$(run_fw $args)" in
+    *UFW:*) echo "FAIL run_fw $args must leave ufw alone"; fails=$((fails + 1)) ;;
+    *) echo "PASS run_fw $args leaves ufw alone" ;;
+  esac
+done
+
+k3fblock="$(awk '/^configure_k3s_firewall\(\) \{/,/^}/' "$BS")"
+[ -n "$k3fblock" ] || { echo "FAIL: no configure_k3s_firewall found in $BS"; exit 1; }
+vfblock="$(awk '/^configure_velocity_firewall\(\) \{/,/^}/' "$BS")"
+[ -n "$vfblock" ] || { echo "FAIL: no configure_velocity_firewall found in $BS"; exit 1; }
+run_host_fw() { # ufw-state firewalld(0|1)
+  UFW="$1" FIREWALLD="$2" POD_CIDR=10.42.0.0/16 SERVICE_CIDR=10.43.0.0/16 FELIS_PANEL_NODEPORT=30443 \
+  FELIS_GAME_PORT=25565 bash -c '
+    log() { printf "LOG: %s\n" "$*"; }
+    systemctl() { [ "$FIREWALLD" = 1 ]; }
+    firewall-cmd() { printf "FW: %s\n" "$*"; }
+    '"$ufw_stub"'
+    '"$ublock"'
+    '"$k3fblock"'
+    '"$vfblock"'
+    configure_k3s_firewall
+    configure_velocity_firewall' 2>&1
+}
+out="$(run_host_fw active 0)"
+expect "ufw admits the pods" "UFW: allow from 10.42.0.0/16 comment felis-k3s-pods" "$out"
+expect "ufw admits the services" "UFW: allow from 10.43.0.0/16 comment felis-k3s-services" "$out"
+expect "ufw opens the panel NodePort" "UFW: allow 30443/tcp comment felis-panel" "$out"
+expect "ufw opens the game port" "UFW: allow 25565/tcp comment felis-proxy" "$out"
+case "$out" in
+  *"UFW: allow 6443"*) echo "FAIL ufw must not open the API server to the network:"; echo "$out"; fails=$((fails + 1)) ;;
+  *) echo "PASS ufw keeps the API server closed to the network" ;;
+esac
+case "$out" in
+  *FW:*--add*) echo "FAIL an inactive firewalld must be left alone:"; echo "$out"; fails=$((fails + 1)) ;;
+  *) echo "PASS ufw alone leaves firewalld alone" ;;
+esac
+out="$(run_host_fw inactive 1)"
+case "$out" in
+  *UFW:*) echo "FAIL an inactive ufw must be left alone:"; echo "$out"; fails=$((fails + 1)) ;;
+  *) echo "PASS an inactive ufw is left alone" ;;
+esac
+expect "  while firewalld still gets the pods" "FW: --permanent --zone=trusted --add-source=10.42.0.0/16" "$out"
+
 expect "a routable bind with no proxy CIDR is warned about" "WARNING: bound to 10.0.0.5:8081 with no FELIS_NANO_PROXY_CIDR" \
   "$(run_summary 10.0.0.5:8081)"
 expect "a routable bind with a proxy CIDR names it" "admits 8081/tcp only from" \
diff --git a/deploy/uninstall.sh b/deploy/uninstall.sh
index 523c0b5..810147a 100644
--- a/deploy/uninstall.sh
+++ b/deploy/uninstall.sh
@@ -133,7 +133,7 @@ confirm() {
 print_plan() {
   log "this will remove from $(uname -n):"
   log "  the felis-* systemd units, cloudflared-felis.service, the ${VELOCITY_USER} user,"
-  log "  ${OPT_DIR}, ${HOST_BIN}, the felis_postgres and felis_edge nftables tables and the firewalld openings"
+  log "  ${OPT_DIR}, ${HOST_BIN}, the felis_postgres and felis_edge nftables tables and the firewalld and ufw openings"
   case "$K3S_MODE" in
     remove) log "  k3s, with everything in it (${K3S_BIN_DIR}/k3s-uninstall.sh)" ;;
     keep) log "  Felis's namespaces (${FELIS_NAMESPACES[*]}) and the ${FELIS_CRD} CRD; k3s stays" ;;
@@ -244,6 +244,35 @@ remove_firewalld_rules() { # game-port nano-port
   fi
 }
 
+# remove_ufw_rules takes back the ufw rules the installer added, found by their felis-
+# comments (configure_k3s_firewall and its neighbours in bootstrap.sh). The k3s ranges stay
+# when k3s does, and go with it or when it is already gone. ufw lists a rule's IPv6 twin
+# under its own number, and each delete renumbers the rules after it, so they go from the
+# highest number down.
+remove_ufw_rules() {
+  command -v ufw >/dev/null 2>&1 || return 0
+  local status nums n keep_k3s=1
+  status="$(LC_ALL=C ufw status numbered 2>/dev/null)" || return 0
+  [ "$(printf '%s\n' "$status" | head -n 1)" = "Status: active" ] || return 0
+  [ "$K3S_MODE" = keep ] || keep_k3s=""
+  nums="$(printf '%s\n' "$status" | awk -v keep_k3s="$keep_k3s" '
+    match($0, /# felis-[a-z0-9-]+ *$/) {
+      tag = substr($0, RSTART + 2)
+      sub(/ +$/, "", tag)
+      if (keep_k3s != "" && tag ~ /^felis-k3s-/) next
+      if (match($0, /^\[ *[0-9]+\]/)) {
+        n = substr($0, RSTART + 1, RLENGTH - 2)
+        gsub(/ /, "", n)
+        print n
+      }
+    }' | sort -rn)"
+  [ -n "$nums" ] || return 0
+  for n in $nums; do
+    ufw --force delete "$n" >/dev/null
+  done
+  ok "ufw rules removed"
+}
+
 # retain_volumes_in_cluster keeps every volume Felis's claims are bound to when the
 # namespaces go: local-path deletes a Delete-policy volume's directory with its claim.
 retain_volumes_in_cluster() {
@@ -496,6 +525,7 @@ main() {
   esac
   remove_nft_tables
   remove_firewalld_rules "$game" "$nano"
+  remove_ufw_rules
   remove_host_files
   purge_database
   purge_images
diff --git a/deploy/uninstall_test.sh b/deploy/uninstall_test.sh
index e2ae492..b155565 100644
--- a/deploy/uninstall_test.sh
+++ b/deploy/uninstall_test.sh
@@ -114,6 +114,14 @@ run_uninstall() {
           esac ;;
       esac
     }
+    # UFW_STATUS: what `ufw status numbered` answers; ufw translates it outside the C locale.
+    ufw() {
+      case "$*" in
+        "status numbered")
+          if [ "${LC_ALL:-}" = C ]; then printf "%s\n" "${UFW_STATUS:-Status: inactive}"; else echo "状态：激活"; fi ;;
+        *) echo "UFW $*" >> "$calls" ;;
+      esac
+    }
     docker() { echo "DOCKER $*" >> "$calls"; }
     userdel() { echo "USERDEL $*" >> "$calls"; }
     uname() { echo testhost; }
@@ -313,6 +321,57 @@ for u in $(sed -n 's|^[A-Z_]*="/etc/systemd/system/\([^"]*\)"$|\1|p' "$(dirname
   expect "the uninstaller removes $u" " $u" " $(printf '%s' "$units" | tr '\n' ' ')"
 done
 
+# --- ufw: the rules bootstrap added, by the comments bootstrap gives them ------------------
+# The listing is what `ufw status numbered` prints once bootstrap has run: a rule of the
+# operator's own first (commented, as an operator may), then each felis- rule bootstrap.sh can
+# add and its IPv6 twin.
+tags="$(grep -o 'comment felis-[a-z0-9-]*' "$(dirname "$US")/bootstrap.sh" | awk '{ print $2 }' | sort -u)"
+case " $(printf '%s ' $tags)" in
+  *" felis-k3s-pods "*" felis-proxy "*) echo "PASS bootstrap tags its ufw rules" ;;
+  *) echo "FAIL bootstrap.sh adds no felis-k3s-pods and felis-proxy ufw rules: <$tags>"; fails=$((fails + 1)) ;;
+esac
+listing="Status: active
+
+     To                         Action      From
+     --                         ------      ----
+[ 1] 22/tcp                     ALLOW IN    Anywhere                    # ssh"
+n=1
+for twin in "" " (v6)"; do
+  for t in $tags; do
+    n=$((n + 1))
+    listing="${listing}
+$(printf '[%2d] Rule%-22s ALLOW IN    Anywhere%-19s # %s' "$n" "$twin" "$twin" "$t")"
+  done
+done
+listing="${listing}
+$(printf '[%2d] 22/tcp (v6)                ALLOW IN    Anywhere (v6)' "$((n + 1))")"
+# numbers <listing> <regex>: the rule numbers whose line matches, highest first.
+numbers() { printf '%s\n' "$1" | grep -E "$2" | sed 's/^\[ *\([0-9]*\)\].*/\1/' | sort -rn | paste -sd ' ' -; }
+deletes() { grep '^UFW --force delete' "$root/calls" | awk '{ print $4 }' | paste -sd ' ' -; }
+
+fresh_host
+out="$(UFW_STATUS="$listing" run_uninstall "default felis minecraft" --yes)"
+want="$(numbers "$listing" '# felis-')"
+[ -n "$want" ] && [ "$(deletes)" = "$want" ] \
+  && echo "PASS a Felis-only cluster's uninstall deletes every felis- ufw rule, highest first" \
+  || { echo "FAIL a Felis-only cluster: deleted <$(deletes)>, want <$want>"; fails=$((fails + 1)); }
+case " $(deletes) " in
+  *" 1 "* | *" $((n + 1)) "*) echo "FAIL the operator's own ufw rules were deleted: $(deletes)"; fails=$((fails + 1)) ;;
+  *) echo "PASS the operator's own ufw rules stay" ;;
+esac
+expect "  and says so" "ufw rules removed" "$out"
+
+fresh_host
+UFW_STATUS="$listing" run_uninstall "default kube-system felis minecraft felis-build shop" --yes >/dev/null
+[ "$(deletes)" = "$(numbers "$listing" '# felis-' | tr ' ' '\n' | grep -vxE "$(numbers "$listing" '# felis-k3s-' | tr ' ' '|')" | paste -sd ' ' -)" ] \
+  && echo "PASS a k3s that stays keeps its pod and service ranges in ufw" \
+  || { echo "FAIL a kept k3s: deleted <$(deletes)>, listing:"; echo "$listing"; fails=$((fails + 1)); }
+
+fresh_host
+UFW_STATUS="Status: inactive" run_uninstall "default felis minecraft" --yes >/dev/null
+[ -z "$(deletes)" ] && echo "PASS an inactive ufw is left alone" \
+  || { echo "FAIL an inactive ufw: deleted <$(deletes)>"; fails=$((fails + 1)); }
+
 # The database's cluster and the move's marker are where bootstrap put them, or keep-data
 # and purge act on a directory that is not there.
 paths="$(FELIS_UNINSTALL_SOURCED=1 bash -c '. "$0"; printf "%s %s\n" "$PG_DATA_DIR" "$PG_MOVED_MARKER"' "$US")"
diff --git a/docs/operations.md b/docs/operations.md
index f390713..b93b33a 100644
--- a/docs/operations.md
+++ b/docs/operations.md
@@ -68,6 +68,17 @@ once, then stops with nothing touched **[SH-TESTED]**:
 `FELIS_PREFLIGHT=warn` reports the same problems as warnings and installs anyway, for a
 host the checks misjudge.
 
+A host firewall is opened, never turned off **[SH-TESTED]**. With firewalld active the
+installer adds the panel NodePort, the game port and 6443, and puts k3s's pod and service
+ranges in the trusted zone. With ufw enabled (common on Ubuntu and Debian, and enabled in
+the CI install **[CI]**) it admits `10.42.0.0/16` and `10.43.0.0/16`, the panel NodePort and
+the game port, each rule commented `felis-…`; 6443 stays closed to the network, since pods
+reach the API server from their own range. Felis-nano opens its port to
+`FELIS_NANO_PROXY_CIDR` alone in either. `uninstall.sh` removes these again, the k3s ranges
+only when k3s goes too. Any other firewall in front of the host must admit the same:
+dropped pod traffic shows up as the first rollout timing out ("control-plane rollout did
+not complete").
+
 Two things the host must keep for as long as the install lives:
 
 - **Its address.** The install is bound to the IPv4 address it was made on (the k3s
@@ -266,8 +277,8 @@ Both modes remove the `felis-*` systemd units and `cloudflared-felis.service`, t
 Velocity user, `/opt/felis`, `/usr/local/bin/felis`, the release assets an interrupted
 install left in `/var/lib/felis/artifacts`, the installer's cloudflared binary (unless
 another unit runs it), the `felis_edge` nftables table (and `felis_postgres`, which
-releases before the database moved into k3s loaded) and the firewalld ports the installer
-opened. k3s goes with k3s's own `k3s-uninstall.sh` when the cluster holds nothing but
+releases before the database moved into k3s loaded), the firewalld ports the installer
+opened and its `felis-`-commented ufw rules. k3s goes with k3s's own `k3s-uninstall.sh` when the cluster holds nothing but
 Felis's namespaces; when it runs anything else only `felis`, `minecraft`, `felis-build`
 and the MinecraftServer CRD are deleted.
 `--keep-k3s` and `--remove-k3s` override that choice.