Harden against set -e/pipefail crashes and sed marker edge cases

Fixes from a two-agent bug review, all verified:
- active_uplink/tether_ip never fail (bare assignments were killing the
  TUI when offline or on mid-check unplug; netns-tested)
- all TUI menu actions guarded with || true; risky steps inside
  cmd_install/tui_switch/revive_usbmuxd individually guarded since
  || true disables errexit inside the callee
- pause on tui_connect error paths so warnings survive the redraw
- tui_switch: require non-empty uplink before claiming success
- strip_windowrules refuses to range-delete without the end marker;
  newline guard before append (both fixture-tested)
- probes drain output instead of grep -q (pipefail SIGPIPE)
- removed dead pair_wait; quoted .desktop Exec path; priority rejects
  unknown args; unpair reports failure; help no longer prints set line

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

omatether.sh

@@ -40,21 +40,26 @@ tether_iface() {
   return 1
 }
 
-phone_on_usb()  { lsusb 2>/dev/null | grep -qi 'apple.*iphone'; }
+# Probes drain output fully ([[ -n $(...) ]]) rather than grep -q, which can
-phone_visible() { idevice_id -l 2>/dev/null | grep -q .; }
+# SIGPIPE the producer and misreport under pipefail.
+phone_on_usb()  { [[ -n $(lsusb 2>/dev/null | grep -i 'apple.*iphone' || true) ]]; }
+phone_visible() { [[ -n $(idevice_id -l 2>/dev/null || true) ]]; }
 phone_paired()  { idevicepair validate >/dev/null 2>&1; }
 
 phone_name() { ideviceinfo -k DeviceName 2>/dev/null || echo "iPhone"; }
 
+# Both must never fail: bare `x=$(...)` assignments under set -e abort the
+# whole script (and close the TUI window) if the pipeline fails — which
+# happens when the interface vanishes mid-check or no default route exists.
 tether_ip() {
   local iface=$1
-  ip -4 -br addr show "$iface" 2>/dev/null | awk '{print $3}'
+  ip -4 -br addr show "$iface" 2>/dev/null | awk '{print $3}' || true
 }
 
-# Interface currently carrying the default route.
+# Interface currently carrying the default route (empty if offline).
 active_uplink() {
   ip route get 1.1.1.1 2>/dev/null \
-    | awk '{for(i=1;i<NF;i++) if($i=="dev"){print $(i+1); exit}}'
+    | awk '{for(i=1;i<NF;i++) if($i=="dev"){print $(i+1); exit}}' || true
 }
 
 current_metric() {
@@ -69,7 +74,7 @@ net_test() {
 # usbmuxd drops devices that were plugged in before it started
 # ("device unconfigured") — a restart rescans the bus.
 revive_usbmuxd() {
-  as_root systemctl restart usbmuxd
+  as_root systemctl restart usbmuxd || { warn "Could not restart usbmuxd (sudo declined?)"; return 1; }
   sleep 2
 }
 
@@ -111,14 +116,31 @@ reload_networkd() {
   fi
 }
 
+# Delete our marker-delimited block. Only range-delete when BOTH markers are
+# present — with the end marker missing, sed's range would eat everything
+# from the begin marker to EOF, including unrelated user config.
+strip_windowrules() {
+  grep -q '>>> omatether windowrules begin' "$WINDOWS_CONF" || return 0
+  if ! grep -q '<<< omatether windowrules end' "$WINDOWS_CONF"; then
+    warn "windows.conf has our begin marker but no end marker — leaving it untouched."
+    return 1
+  fi
+  sed -i '/>>> omatether windowrules begin/,/<<< omatether windowrules end/d' "$WINDOWS_CONF"
+}
+
 # Small centered floating window for the TUI (user-level Hyprland rule;
 # remove-then-append so re-installs stay idempotent).
 install_windowrules() {
   [[ -f $WINDOWS_CONF ]] || return 0   # not a Hyprland/Omarchy box — skip
   if ! grep -q 'omatether windowrules begin' "$WINDOWS_CONF"; then
-    cp "$WINDOWS_CONF" "$WINDOWS_CONF.bak.$(date +%s)"
+    cp "$WINDOWS_CONF" "$WINDOWS_CONF.bak.$(date +%s)" || return 1
+  fi
+  strip_windowrules || return 1
+  # Ensure the file ends with a newline, or our begin marker glues onto the
+  # last existing line and the next strip would delete that line too.
+  if [[ -s $WINDOWS_CONF && $(tail -c1 "$WINDOWS_CONF") != "" ]]; then
+    printf '\n' >> "$WINDOWS_CONF"
   fi
-  sed -i '/>>> omatether windowrules begin/,/<<< omatether windowrules end/d' "$WINDOWS_CONF"
   cat >> "$WINDOWS_CONF" <<'EOF'
 # >>> omatether windowrules begin
 # omatether — small floating window, centered.
@@ -132,19 +154,23 @@ EOF
 
 remove_windowrules() {
   [[ -f $WINDOWS_CONF ]] || return 0
-  sed -i '/>>> omatether windowrules begin/,/<<< omatether windowrules end/d' "$WINDOWS_CONF"
+  strip_windowrules || return 1
   hyprctl reload >/dev/null 2>&1 || true
 }
 
 # --------------------------------------------------------- CLI commands ----
 
+# NOTE: every risky step is explicitly guarded — the TUI calls this with
+# `|| true`, which disables errexit inside the function, so an unguarded
+# failure would otherwise plow on into the next step.
 cmd_install() {
   say "Installing iPhone USB tethering support…"
-  as_root pacman -S --needed --noconfirm usbmuxd libimobiledevice gum
+  as_root pacman -S --needed --noconfirm usbmuxd libimobiledevice gum \
+    || { warn "Package install failed — no internet, or sudo declined."; return 1; }
   ok "usbmuxd + libimobiledevice installed (usbmuxd starts on demand via udev)"
 
-  write_netfile "$METRIC_FALLBACK"
+  write_netfile "$METRIC_FALLBACK" || { warn "Could not write $NETFILE."; return 1; }
-  reload_networkd
+  reload_networkd || { warn "networkd reload failed."; return 1; }
   ok "networkd profile written: $NETFILE (fallback priority, metric $METRIC_FALLBACK)"
 
   # Floating TUI launcher for Walker. Uses a dedicated app-id (rather than
@@ -156,21 +182,21 @@ cmd_install() {
 [Desktop Entry]
 Name=iPhone Tether
 Comment=Use an iPhone's internet over USB
-Exec=xdg-terminal-exec --app-id=omatether -e $self
+Exec=xdg-terminal-exec --app-id=omatether -e "$self"
 Icon=phone
 Terminal=false
 Type=Application
 Categories=Network;
 EOF
   systemctl --user restart elephant.service 2>/dev/null || true
-  install_windowrules
+  install_windowrules || warn "Windowrule install skipped — see above."
   ok "Walker launcher installed: 'iPhone Tether' (small floating window)"
 
   # If the phone was plugged in before usbmuxd existed it won't be seen yet;
   # restart usbmuxd to rescan. (Do NOT `udevadm trigger` — re-firing add
   # events on a connected iPhone wedges it: "device unconfigured".)
   if phone_on_usb && ! phone_visible; then
-    revive_usbmuxd
+    revive_usbmuxd || true
   fi
 
   say ""
@@ -193,20 +219,10 @@ do_pair_once() {
   return 1
 }
 
-# Retry pairing until it succeeds or times out (arg: seconds, default 120).
-pair_wait() {
-  local deadline=$(( SECONDS + ${1:-120} ))
-  while (( SECONDS < deadline )); do
-    idevicepair pair >/dev/null 2>&1 && return 0
-    sleep 5
-  done
-  return 1
-}
-
 cmd_pair() {
   command -v idevicepair >/dev/null || die "libimobiledevice not installed — run: $0 install"
   if ! phone_visible; then
-    phone_on_usb && revive_usbmuxd
+    if phone_on_usb; then revive_usbmuxd || true; fi
     phone_visible || die "No iPhone detected over USB. Plug it in and try again."
   fi
 
@@ -220,7 +236,11 @@ cmd_pair() {
 }
 
 cmd_unpair() {
-  idevicepair unpair && ok "Unpaired."
+  if idevicepair unpair; then
+    ok "Unpaired."
+  else
+    die "Unpair failed — is a phone connected and paired?"
+  fi
 }
 
 cmd_status() {
@@ -246,7 +266,7 @@ cmd_status() {
     addr=$(tether_ip "$iface")
     if [[ -n $addr ]]; then
       ok "IPv4: $addr"
-      ip route show default dev "$iface" | sed 's/^/  /'
+      ip route show default dev "$iface" 2>/dev/null | sed 's/^/  /' || true
       if net_test "$iface"; then
         ok "Internet via $iface works"
       else
@@ -264,26 +284,29 @@ cmd_priority() {
   [[ -f $NETFILE ]] || die "Not installed — run: $0 install"
   case ${1:-} in
     high)
-      write_netfile "$METRIC_PREFERRED"
+      write_netfile "$METRIC_PREFERRED" || die "Could not write $NETFILE."
-      reload_networkd
+      reload_networkd || die "networkd reload failed."
       ok "Tether now PREFERRED (metric $METRIC_PREFERRED) — traffic routes via the phone when plugged in"
       ;;
     low)
-      write_netfile "$METRIC_FALLBACK"
+      write_netfile "$METRIC_FALLBACK" || die "Could not write $NETFILE."
-      reload_networkd
+      reload_networkd || die "networkd reload failed."
       ok "Tether now FALLBACK (metric $METRIC_FALLBACK) — ethernet/wifi win when available"
       ;;
-    *)
+    "")
       say "Current metric: $(current_metric)  (ethernet=100, wifi=600)"
       say "Usage: $0 priority <high|low>"
       ;;
+    *)
+      die "Unknown priority '$1' — use high or low."
+      ;;
   esac
 }
 
 cmd_uninstall() {
   as_root rm -f "$NETFILE"
   rm -f "$DESKTOP_FILE"
-  remove_windowrules
+  remove_windowrules || warn "Windowrule removal skipped — see above."
   as_root networkctl reload
   systemctl --user restart elephant.service 2>/dev/null || true
   ok "Removed $NETFILE, the Walker launcher and windowrules (usbmuxd/libimobiledevice left installed)"
@@ -330,16 +353,19 @@ tui_header() {
   echo
 }
 
+# Wait for Enter so warnings aren't wiped by the next dashboard redraw.
+pause() { gum input --placeholder "Press Enter to continue…" >/dev/null || true; }
+
 tui_connect() {
   say ""
   if ! phone_visible; then
-    phone_on_usb && revive_usbmuxd
+    if phone_on_usb; then revive_usbmuxd || true; fi
   fi
   if ! phone_visible; then
     # shellcheck disable=SC2016  # expansion happens in the child shell
     gum spin --title "Plug the iPhone in via USB…" -- bash -c \
       'for i in $(seq 1 24); do idevice_id -l 2>/dev/null | grep -q . && exit 0; sleep 5; done; exit 1' \
-      || { warn "No iPhone appeared. Check the cable and try again."; return 1; }
+      || { warn "No iPhone appeared. Check the cable and try again."; pause; return 1; }
   fi
 
   if ! phone_paired; then
@@ -348,7 +374,7 @@ tui_connect() {
     # shellcheck disable=SC2016  # expansion happens in the child shell
     gum spin --title "Waiting for Trust… (unlock the phone)" -- bash -c \
       'for i in $(seq 1 24); do idevicepair pair >/dev/null 2>&1 && exit 0; sleep 5; done; exit 1' \
-      || { warn "Pairing timed out. Unlock the phone and pick Connect again."; return 1; }
+      || { warn "Pairing timed out. Unlock the phone and pick Connect again."; pause; return 1; }
     ok "Paired with $(phone_name)"
   fi
 
@@ -361,31 +387,28 @@ tui_connect() {
     warn "Paired, but no connection yet. On the phone enable:"
     say  "  Settings → Personal Hotspot → Allow Others to Join: ON"
   fi
-  gum input --placeholder "Press Enter to continue…" >/dev/null || true
+  pause
 }
 
 tui_switch() {
-  local target=$1 iface
+  local target=$1 iface metric=$METRIC_FALLBACK
   say ""
-  if [[ $target == phone ]]; then
+  [[ $target == phone ]] && metric=$METRIC_PREFERRED
-    write_netfile "$METRIC_PREFERRED"
+  write_netfile "$metric" || { warn "Could not update $NETFILE (sudo declined?)"; pause; return 1; }
-  else
+  reload_networkd || { warn "networkd reload failed."; pause; return 1; }
-    write_netfile "$METRIC_FALLBACK"
-  fi
-  reload_networkd
   gum spin --title "Applying routes…" -- sleep 3 || true
 
   local uplink
   uplink=$(active_uplink)
   iface=$(tether_iface || true)
-  if [[ $target == phone && $uplink == "$iface" ]]; then
+  if [[ -n $uplink && $target == phone && $uplink == "$iface" ]]; then
     ok "All traffic now routes via the iPhone ($iface)"
-  elif [[ $target == normal && $uplink != "$iface" ]]; then
+  elif [[ -n $uplink && $target == normal && $uplink != "$iface" ]]; then
-    ok "Back to normal — traffic routes via ${uplink:-your usual connection}"
+    ok "Back to normal — traffic routes via $uplink"
   else
     warn "Route didn't settle as expected (uplink: ${uplink:-none}). Check Status."
   fi
-  gum input --placeholder "Press Enter to continue…" >/dev/null || true
+  pause
 }
 
 cmd_tui() {
@@ -466,12 +489,14 @@ cmd_tui() {
     local choice
     choice=$(gum choose --header "$(printf '%*s%s' "$((mpad + 2))" '' 'What do you want to do?')" "${pmenu[@]}") || break
     choice=${choice#"${choice%%[![:space:]]*}"}   # trim the centering pad
+    # Every action is guarded with || true: a non-zero return from a bare
+    # call here would trip set -e and close the TUI window without a trace.
     case $choice in
-      "Install tethering support")      cmd_install; gum input --placeholder "Press Enter…" >/dev/null || true ;;
+      "Install tethering support")      cmd_install || true; pause ;;
-      "Connect phone")                  tui_connect ;;
+      "Connect phone")                  tui_connect || true ;;
-      "Switch internet → iPhone")       tui_switch phone ;;
+      "Switch internet → iPhone")       tui_switch phone || true ;;
-      "Switch back → ethernet/wifi")    tui_switch normal ;;
+      "Switch back → ethernet/wifi")    tui_switch normal || true ;;
-      "Status (full check)")            say ""; cmd_status || true; gum input --placeholder "Press Enter…" >/dev/null || true ;;
+      "Status (full check)")            say ""; cmd_status || true; pause ;;
       "Refresh")                        ;;
       "Quit"|"")                        break ;;
     esac
@@ -489,7 +514,7 @@ case ${1:-tui} in
   priority)  shift; cmd_priority "${1:-}" ;;
   uninstall) cmd_uninstall ;;
   help|-h|--help)
-    sed -n '2,11p' "$0" | sed 's/^# \{0,1\}//'
+    sed -n '2,10p' "$0" | sed 's/^# \{0,1\}//'
     ;;
   *) die "Unknown command: $1 (try: $0 help)" ;;
 esac