fix: center the loading placeholder on an a switch

wttrin-query inserted the "Loading weather for ..." placeholder but never centered it, leaving that to window-configuration-change-hook. On an `a` switch the *wttr.in* buffer is already displayed, so the hook doesn't fire. The placeholder kept the previous weather block's window margin and rendered off-center until the new weather arrived.

I moved the placeholder rendering into wttrin--render-loading-placeholder, which centers it explicitly via wttrin--update-layout. It no longer depends on the hook, so the placeholder is centered on the first open and through every switch.

2 files changed, 84 insertions, 8 deletions

diff --git a/tests/test-wttrin--render-loading-placeholder.el b/tests/test-wttrin--render-loading-placeholder.el
new file mode 100644
index 0000000..5c27557
--- /dev/null
+++ b/tests/test-wttrin--render-loading-placeholder.el
@@ -0,0 +1,64 @@
+;;; test-wttrin--render-loading-placeholder.el --- Loading placeholder centering -*- lexical-binding: t; -*-
+
+;; Copyright (C) 2026 Craig Jennings
+
+;;; Commentary:
+;; The loading placeholder must be centered every time it is shown, including on
+;; an `a' switch where the *wttr.in* buffer is already displayed.  In that case
+;; `window-configuration-change-hook' does not fire, so `wttrin-query' relied on
+;; a stale window margin from the previous weather and the placeholder rendered
+;; off-center.  `wttrin--render-loading-placeholder' centers it explicitly.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+(require 'wttrin)
+
+(ert-deftest test-wttrin--render-loading-placeholder-normal-shows-display-name ()
+  "Normal: the placeholder text names the display string, not the raw query."
+  (with-temp-buffer
+    (cl-letf (((symbol-function 'wttrin--update-layout) #'ignore))
+      (wttrin--render-loading-placeholder "1500 Sugar Bowl Dr" "Superdome")
+      (should (string-match-p "Loading weather for Superdome\\.\\.\\."
+                              (buffer-string)))
+      (should-not wttrin--weather-rendered))))
+
+(ert-deftest test-wttrin--render-loading-placeholder-boundary-nil-display-uses-query ()
+  "Boundary: with no display name, the placeholder falls back to the query."
+  (with-temp-buffer
+    (cl-letf (((symbol-function 'wttrin--update-layout) #'ignore))
+      (wttrin--render-loading-placeholder "Reykjavik" nil)
+      (should (string-match-p "Loading weather for Reykjavik" (buffer-string))))))
+
+(ert-deftest test-wttrin--render-loading-placeholder-normal-centers-via-layout ()
+  "Normal: rendering the placeholder runs the layout pass, so it is centered by
+the same path weather uses rather than left to the hook (which does not fire on
+a reused, already-displayed buffer)."
+  (with-temp-buffer
+    (let ((layout-calls 0))
+      (cl-letf (((symbol-function 'wttrin--update-layout)
+                 (lambda (&rest _) (setq layout-calls (1+ layout-calls)))))
+        (wttrin--render-loading-placeholder "Reykjavik" "Reykjavik")
+        (should (= 1 layout-calls))))))
+
+(ert-deftest test-wttrin--render-loading-placeholder-regression-replaces-stale-margin ()
+  "Regression: a stale window margin left by the previous weather block is
+recomputed for the placeholder, so it no longer renders at the old margin after
+an `a' switch."
+  (let ((buf (get-buffer-create "*wttrin-ph-test*")))
+    (unwind-protect
+        (save-window-excursion
+          (set-window-buffer (selected-window) buf)
+          ;; A wide margin as if left over from a previous (wide) weather block.
+          (set-window-margins (selected-window) 40)
+          (with-current-buffer buf
+            (let ((wttrin-auto-fit-font nil))
+              (wttrin--render-loading-placeholder "Reykjavik" "Reykjavik")
+              ;; The placeholder path must have recomputed the margin, not left
+              ;; the stale 40 in place.
+              (should-not (equal 40 (car (window-margins (selected-window))))))))
+      (kill-buffer buf))))
+
+(provide 'test-wttrin--render-loading-placeholder)
+;;; test-wttrin--render-loading-placeholder.el ends here
diff --git a/wttrin.el b/wttrin.el
index 8bfa74e..dd821b6 100644
--- a/wttrin.el
+++ b/wttrin.el
@@ -1310,6 +1310,25 @@ coordinates but can name the place)."
 (defvar-local wttrin--current-request-id nil
   "Request id of the most recent query for this weather buffer.")
 
+(defun wttrin--render-loading-placeholder (query display)
+  "Show the loading placeholder for QUERY in the current buffer.
+DISPLAY is the name to show (a saved-location name); when nil it falls back to
+QUERY.  Erases the buffer, inserts the one-line placeholder, resets the font to
+the base height (dropping any auto-fit remap from the previous weather), and
+centers it via `wttrin--update-layout'.  The explicit centering matters on an
+`a' switch: the *wttr.in* buffer is already displayed, so
+`window-configuration-change-hook' does not fire and the placeholder would
+otherwise keep the previous weather block's window margin."
+  (let ((inhibit-read-only t))
+    (erase-buffer)
+    (insert "Loading weather for " (or display query) "..."))
+  (setq buffer-read-only t)
+  ;; The placeholder is one line; keep auto-fit off it (weather not yet rendered)
+  ;; and show it at the base font rather than the previous weather's size.
+  (setq-local wttrin--weather-rendered nil)
+  (wttrin--reset-font-height)
+  (wttrin--update-layout))
+
 (defun wttrin-query (query &optional display address)
   "Asynchronously query weather for QUERY, display the result when ready.
 QUERY is what weather is fetched by (and the cache key).  Optional DISPLAY is
@@ -1319,15 +1338,8 @@ coordinates from a geolocation command."
   (let ((buffer (get-buffer-create (format "*wttr.in*")))
         (request-id (setq wttrin--request-counter (1+ wttrin--request-counter))))
     (switch-to-buffer buffer)
-    (setq buffer-read-only nil)
-    (erase-buffer)
-    (insert "Loading weather for " (or display query) "...")
-    (setq buffer-read-only t)
     (setq-local wttrin--current-request-id request-id)
-    ;; The placeholder is one line; keep auto-fit off it and show it at the base
-    ;; font rather than the previous weather's auto-fitted (possibly capped) size.
-    (setq-local wttrin--weather-rendered nil)
-    (wttrin--reset-font-height)
+    (wttrin--render-loading-placeholder query display)
     (wttrin--get-cached-or-fetch
      query
      (lambda (raw-string &optional error-msg)