From 3ed48163aaf77003659cf6e53c2594be51acddd7 Mon Sep 17 00:00:00 2001
From: vicrodh <103399283+vicrodh@users.noreply.github.com>
Date: Sun, 23 Aug 2026 16:58:16 -0600
Subject: [PATCH] fix(library): correct Tracks viewport restoration

Restore the semantic anchor in viewport coordinates and suppress lazy-page requests while the ListView is being repositioned. This avoids treating content coordinates as screen offsets and prevents recursive page loads during restoration.

cx
---
 crates/qbz-qt/qml/views/local/LocalTracksTab.qml | 16 +++++++++++++---
 crates/qbz-qt/src/local_state.rs                 |  7 ++++++-
 2 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/crates/qbz-qt/qml/views/local/LocalTracksTab.qml b/crates/qbz-qt/qml/views/local/LocalTracksTab.qml
index b45cc2734..497045c05 100644
--- a/crates/qbz-qt/qml/views/local/LocalTracksTab.qml
+++ b/crates/qbz-qt/qml/views/local/LocalTracksTab.qml
@@ -33,6 +33,9 @@ Item {
     // contentY change before that property turns true. All of those changes
     // describe the same page miss and must collapse into one bridge call.
     property bool pageRequestPending: false
+    // Programmatic viewport restoration emits the same Flickable signals as
+    // user input. Keep those signals from recursively requesting another page.
+    property bool restoringPageAnchor: false
     // Invalidates a deferred viewport restore when another document/model
     // replacement wins before Qt's next event-loop turn.
     property int entriesEpoch: 0
@@ -40,6 +43,7 @@ Item {
     function requestNextPage(force) {
         if (root.nativeModelActive
             || root.pageRequestPending
+            || root.restoringPageAnchor
             || !QbzLocal.localTracksHasMore
             || QbzLocal.localTracksLoadingMore
             || QbzLocal.localTracksLoading)
@@ -88,8 +92,12 @@ Item {
         return {
             "id": String(root.entries[i].row.id),
             // Position inside the viewport, including a partially clipped
-            // first row or a group header immediately above it.
-            "screenY": cell ? cell.mapToItem(list, 0, 0).y : 0
+            // first row or a group header immediately above it. A ListView
+            // delegate's y is in contentItem coordinates, so subtracting the
+            // viewport's contentY is the visual coordinate. mapToItem(list)
+            // preserves the content coordinate here and would add thousands
+            // of rows back into the restore calculation.
+            "screenY": cell ? cell.y - list.contentY : 0
         }
     }
 
@@ -115,15 +123,17 @@ Item {
         Qt.callLater(function () {
             if (epoch !== root.entriesEpoch || root.nativeModelActive)
                 return
+            root.restoringPageAnchor = true
             list.forceLayout()
             list.positionViewAtIndex(target, ListView.Beginning)
             list.forceLayout()
             var cell = list.itemAtIndex(target)
-            var currentScreenY = cell ? cell.mapToItem(list, 0, 0).y : 0
+            var currentScreenY = cell ? cell.y - list.contentY : 0
             var wanted = list.contentY + currentScreenY - anchor.screenY
             var minY = list.originY
             var maxY = minY + Math.max(0, list.contentHeight - list.height)
             list.contentY = Math.max(minY, Math.min(wanted, maxY))
+            root.restoringPageAnchor = false
             root.reportSoon()
         })
     }
diff --git a/crates/qbz-qt/src/local_state.rs b/crates/qbz-qt/src/local_state.rs
index 6a86c15a5..f4f2eeb26 100644
--- a/crates/qbz-qt/src/local_state.rs
+++ b/crates/qbz-qt/src/local_state.rs
@@ -528,7 +528,12 @@ mod phase_a_tests {
         let qml = include_str!("../qml/views/local/LocalTracksTab.qml");
         assert!(qml.contains("function capturePageAnchor()"));
         assert!(qml.contains("String(root.entries[i].row.id)"));
-        assert!(qml.contains("cell.mapToItem(list, 0, 0).y"));
+        assert!(qml.contains("cell.y - list.contentY"));
+        assert!(!qml.contains("cell.mapToItem(list"));
+        assert!(qml.contains("|| root.restoringPageAnchor"));
+        assert!(qml.contains(
+            "var wanted = list.contentY + currentScreenY - anchor.screenY"
+        ));
         assert!(qml.contains("function restorePageAnchor(anchor, nextEntries, epoch)"));
         assert!(qml.contains("Qt.callLater(function ()"));
         assert!(qml.contains("list.positionViewAtIndex(target, ListView.Beginning)"));