fix: mode-line tooltip always shows "Updated just now"

The tooltip was a static string computed at fetch time. Since every
successful fetch sets the cache timestamp to now and immediately
renders the tooltip, it was always "just now".

Extract wttrin--mode-line-tooltip as a named function that computes
age from the cache at call time. Set help-echo to this function so
Emacs invokes it on hover, producing an accurate age like
"Updated 12 minutes ago".

1 files changed, 4 insertions, 2 deletions

diff --git a/tests/test-wttrin--mode-line-update-display.el b/tests/test-wttrin--mode-line-update-display.el
index e23780b..81fbded 100644
--- a/tests/test-wttrin--mode-line-update-display.el
+++ b/tests/test-wttrin--mode-line-update-display.el
@@ -146,7 +146,8 @@
       (cl-letf (((symbol-function 'float-time) (lambda () 1300.0)))
         (setq wttrin--mode-line-cache (cons 1000.0 "Paris: ☀️ +61°F Clear"))
         (wttrin--mode-line-update-display)
-        (let ((tooltip (get-text-property 0 'help-echo wttrin-mode-line-string)))
+        (let* ((help-echo-fn (get-text-property 0 'help-echo wttrin-mode-line-string))
+               (tooltip (funcall help-echo-fn nil nil nil)))
           (should (string-match-p "Paris" tooltip))
           (should (string-match-p "Updated 5 minutes ago" tooltip))))
     (test-wttrin--mode-line-update-display-teardown)))
@@ -162,7 +163,8 @@
           ;; Data is 2000 seconds old, threshold is 2*900=1800 -> stale
           (setq wttrin--mode-line-cache (cons 1000.0 "Paris: ☀️ +61°F Clear"))
           (wttrin--mode-line-update-display)
-          (let ((tooltip (get-text-property 0 'help-echo wttrin-mode-line-string)))
+          (let* ((help-echo-fn (get-text-property 0 'help-echo wttrin-mode-line-string))
+                 (tooltip (funcall help-echo-fn nil nil nil)))
             (should (string-match-p "Stale" tooltip))
             (should (string-match-p "fetch failed" tooltip)))))
     (test-wttrin--mode-line-update-display-teardown)))