Add scroll restoration on browser refresh for SPA pages

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

app/RSpade/Core/Js/Rsx.js

@@ -742,6 +742,13 @@ class Rsx {
      */
     static _SCROLL_STORAGE_KEY = 'rsx_scroll_pos';
 
+    /**
+     * Pending scroll restoration state
+     * Set when a refresh is detected, cleared when restoration succeeds
+     * @private
+     */
+    static _pending_scroll = null;
+
     /**
      * Save scroll position to sessionStorage on scroll (debounced)
      * Called from scroll event listener set up in _restore_scroll_on_refresh
@@ -765,8 +772,8 @@ class Rsx {
     }
 
     /**
-     * Restore scroll position if this is a page refresh
+     * Initialize scroll restoration on page refresh
-     * Uses Performance API to detect reload navigation type
+     * Sets up scroll saving and queues restoration if this is a refresh
      * @private
      */
     static _restore_scroll_on_refresh() {
@@ -784,7 +791,7 @@ class Rsx {
             return;
         }
 
-        // This is a refresh - try to restore scroll position
+        // This is a refresh - load stored scroll position
         const stored = sessionStorage.getItem(Rsx._SCROLL_STORAGE_KEY);
         if (!stored) {
             return;
@@ -796,24 +803,78 @@ class Rsx {
 
             // Only restore if URL matches
             if (scroll_data.url !== current_url) {
+                sessionStorage.removeItem(Rsx._SCROLL_STORAGE_KEY);
                 return;
             }
 
-            // Restore scroll position instantly
+            // Queue the scroll restoration
-            window.scrollTo({
+            Rsx._pending_scroll = { x: scroll_data.x, y: scroll_data.y };
-                left: scroll_data.x,
-                top: scroll_data.y,
-                behavior: 'instant'
-            });
 
-            // Clear stored position after successful restore
+            // Clear stored position (we've loaded it into memory)
             sessionStorage.removeItem(Rsx._SCROLL_STORAGE_KEY);
+
+            // Try first restoration attempt
+            Rsx.try_restore_scroll();
         } catch (e) {
             // Invalid JSON or other error - ignore
             sessionStorage.removeItem(Rsx._SCROLL_STORAGE_KEY);
         }
     }
 
+    /**
+     * Attempt to restore scroll position if pending
+     *
+     * Can be called multiple times during page load. Checks if the page is tall
+     * enough to scroll to the target position. Once successful, subsequent calls
+     * are no-ops until the next page refresh.
+     *
+     * Call this after content that may increase page height has loaded
+     * (e.g., after SPA action on_ready completes).
+     *
+     * @returns {boolean} True if scroll was restored, false if pending/skipped
+     */
+    static try_restore_scroll() {
+        // No pending restoration
+        if (!Rsx._pending_scroll) {
+            return false;
+        }
+
+        const target = Rsx._pending_scroll;
+
+        // Check if page is tall enough to scroll to target position
+        // Page needs to be at least (target.y + viewport height) tall
+        const page_height = document.documentElement.scrollHeight;
+        const viewport_height = window.innerHeight;
+        const min_height_needed = target.y + viewport_height;
+
+        if (page_height < min_height_needed) {
+            // Page not tall enough yet - keep pending for retry
+            console_debug('Spa', `Scroll restore waiting: page ${page_height}px < needed ${min_height_needed}px`);
+            return false;
+        }
+
+        // Page is tall enough - restore scroll position
+        window.scrollTo({
+            left: target.x,
+            top: target.y,
+            behavior: 'instant'
+        });
+
+        // Mark as complete - clear pending state
+        Rsx._pending_scroll = null;
+
+        console_debug('Spa', `Scroll restored to (${target.x}, ${target.y})`);
+        return true;
+    }
+
+    /**
+     * Reset pending scroll state
+     * Called by SPA dispatch to clear any pending restoration from previous navigation
+     */
+    static reset_pending_scroll() {
+        Rsx._pending_scroll = null;
+    }
+
     /* Calling this stops the boot process. */
     static async _rsx_core_boot_stop(reason) {
         console.error(reason);

app/RSpade/Core/SPA/Spa.js

@@ -573,6 +573,10 @@ class Spa {
         // Errors from previous page's pending requests should be ignored for 10 seconds
         Spa._navigation_timestamp = Date.now();
 
+        // Reset any pending scroll restoration from previous navigation
+        // (Browser refresh scroll is handled separately by Rsx._restore_scroll_on_refresh)
+        Rsx.reset_pending_scroll();
+
         try {
             const opts = {
                 history: options.history || 'auto',
@@ -938,6 +942,12 @@ class Spa {
             if (is_last) {
                 // This is the action - set reference but don't wait
                 Spa._action = component;
+
+                // After action is fully ready (on_load + on_ready complete), retry scroll restoration
+                // This handles cases where on_load fetches data that increases page height
+                component.ready().then(() => {
+                    Rsx.try_restore_scroll();
+                });
             } else {
                 // This is a layout
                 // Wait for render to complete (not full ready - we don't need child data to load)