From 862568dafd2e6224e92cda2d1841870982514614 Mon Sep 17 00:00:00 2001
From: Robert Nederhorst <throb@throb.net>
Date: Tue, 17 Mar 2026 08:18:30 -0700
Subject: [PATCH] fix(session): timeline panel not populated on session restore
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Two issues prevented the timeline panel from displaying after loading
a saved session:

1. Race condition in SessionModel: updateViewportCurrentMediaContainer-
   IndexFromBackend() was called before the model tree was fully built.
   The async requestData(childrenRole) populates playlists and their
   children (timelines) progressively, but the container lookup ran
   before the timeline nodes existed. Added a re-trigger of both
   container index lookups at the end of processChildren() when the
   parent type is Session, Container List, or Playlist.

2. QML timeline panel only handled typeRole=="Timeline" in
   viewedMediaSetChanged(). When the restored viewed container is a
   Playlist (which is common — the session stores the Playlist UUID),
   the timeline panel did nothing. Added a Playlist handler that finds
   the first Timeline child in the Playlist's Container List and
   switches the viewed container to it, with async retry if the
   children haven't loaded yet.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
---
 src/ui/qml/session/src/session_model_ui.cpp  | 11 +++++++++
 ui/qml/xstudio/views/timeline/XsTimeline.qml | 24 ++++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/src/ui/qml/session/src/session_model_ui.cpp b/src/ui/qml/session/src/session_model_ui.cpp
index bc4dc8362..f7fa9a371 100644
--- a/src/ui/qml/session/src/session_model_ui.cpp
+++ b/src/ui/qml/session/src/session_model_ui.cpp
@@ -627,6 +627,17 @@ void SessionModel::processChildren(const nlohmann::json &rj, const QModelIndex &
         emit dataChanged(parent_index, parent_index, roles);
     }
 
+    // After populating session/playlist children, re-trigger the viewport and
+    // current container lookup.  On session restore the initial lookup fires
+    // before the model tree is fully built (the children arrive asynchronously),
+    // so timelines inside playlists are not yet findable.  Re-checking here
+    // ensures the timeline panel picks up the active container once its node
+    // actually exists in the tree.
+    if (type == "Session" || type == "Container List" || type == "Playlist") {
+        updateCurrentMediaContainerIndexFromBackend();
+        updateViewportCurrentMediaContainerIndexFromBackend();
+    }
+
     emit jsonChanged();
 
     CHECK_SLOW_WATCHER_FAST()
diff --git a/ui/qml/xstudio/views/timeline/XsTimeline.qml b/ui/qml/xstudio/views/timeline/XsTimeline.qml
index 6a5789b80..5302bc30f 100644
--- a/ui/qml/xstudio/views/timeline/XsTimeline.qml
+++ b/ui/qml/xstudio/views/timeline/XsTimeline.qml
@@ -306,6 +306,30 @@ Rectangle {
                     initTimeline()
                     }}(), 50);
 
+        } else if (viewedMediaSetProperties.index.valid && viewedMediaSetProperties.values.typeRole == "Playlist") {
+            // When restoring a session, the viewed container may be a Playlist
+            // rather than a Timeline.  Find the first Timeline child inside the
+            // Playlist's Container List (row 2) and initialise from it.
+            let containerListIndex = theSessionData.index(2, 0, viewedMediaSetProperties.index)
+            let childCount = theSessionData.rowCount(containerListIndex)
+            for (let i = 0; i < childCount; i++) {
+                let childIndex = theSessionData.index(i, 0, containerListIndex)
+                if (theSessionData.get(childIndex, "typeRole") == "Timeline") {
+                    // Switch the viewed container to this Timeline so the
+                    // playhead and viewport are correctly attached.
+                    theSessionData.viewportCurrentMediaContainerIndex = childIndex
+                    return
+                }
+            }
+            // No timeline children found (or not yet loaded).  If the container
+            // list is empty the data may still be arriving asynchronously, so
+            // retry after a short delay.
+            if (childCount == 0 && !timeline_items.rootIndex.valid) {
+                callbackTimer.setTimeout(function() { return function() {
+                        viewedMediaSetChanged()
+                        }}(), 250);
+            }
+
         } else if (!timeline_items.rootIndex.valid) {
             // if the user has selected something that is not a timeline (playlist,
             // subset etc.), we do  not update our index here (unless the timeline