taffybar: avoid Wayland backend with stale systemd env

When taffybar is started via systemd --user, the manager environment can keep WAYLAND_DISPLAY/HYPRLAND_INSTANCE_SIGNATURE from an older Wayland session even when we're currently running an X11 xmonad session.

This causes taffybar's backend detection to select the Wayland backend, which prevents X11 struts from being applied and leads to incorrect placement.

Add a small wrapper backend detector that checks for an actual wayland socket and, if missing, sanitizes the env so taffybar's internal context uses the X11 backend.

dotfiles/config/taffybar/taffybar.hs

@@ -110,6 +110,45 @@ enableLogger logger level = do
   logger <- getLogger logger
   saveGlobalLogger $ setLevel level logger
 
+-- Systemd --user's manager environment can be stale across logins (e.g. still
+-- containing WAYLAND_DISPLAY from an older session). `detectBackend` will pick
+-- Wayland if WAYLAND_DISPLAY is set, even when no compositor is running.
+--
+-- Prefer a backend that's actually usable, and sanitize the process environment
+-- so taffybar's internal context backend detection makes the same decision.
+detectBackendRobust :: IO Backend
+detectBackendRobust = do
+  mRuntime <- lookupEnv "XDG_RUNTIME_DIR"
+  mWaylandDisplay <- lookupEnv "WAYLAND_DISPLAY"
+  mDisplay <- lookupEnv "DISPLAY"
+  mSessionType <- lookupEnv "XDG_SESSION_TYPE"
+  mHyprSig <- lookupEnv "HYPRLAND_INSTANCE_SIGNATURE"
+
+  let mWaylandPath = do
+        runtime <- mRuntime
+        wl <- mWaylandDisplay
+        guard (not (null runtime) && not (null wl))
+        pure (runtime </> wl)
+
+  waylandOk <- case mWaylandPath of
+    Nothing -> pure False
+    Just wlPath -> do
+      ok <- doesPathExist wlPath
+      when (not ok) $
+        logM "Main" DEBUG $
+          "WAYLAND_DISPLAY is set but no socket at " ++ wlPath ++ "; preferring X11 when available"
+      pure ok
+
+  when (not waylandOk && maybe False (not . null) mDisplay) $ do
+    when (isJust mWaylandDisplay) $ unsetEnv "WAYLAND_DISPLAY"
+    when (isJust mHyprSig) $ unsetEnv "HYPRLAND_INSTANCE_SIGNATURE"
+    when (mSessionType == Just "wayland") $ setEnv "XDG_SESSION_TYPE" "x11"
+
+  case () of
+    _ | waylandOk -> pure BackendWayland
+      | maybe False (not . null) mDisplay -> pure BackendX11
+      | otherwise -> detectBackend
+
 logDebug = do
   global <- getLogger ""
   saveGlobalLogger $ setLevel DEBUG global
@@ -242,7 +281,7 @@ main = do
   enableLogger "Graphics.UI.GIGtkStrut" DEBUG
 
   hostName <- getHostName
-  backend <- detectBackend
+  backend <- detectBackendRobust
   let relativeFiles = fromMaybe ["palette.css", "taffybar.css"] $ lookup hostName cssFilesByHostname
   cssFiles <- mapM (getUserConfigFile "taffybar") relativeFiles