@@ -193,10 +193,12 @@ private static int CountSpans(string path, string spanName, string label) => Fil
         return $"{span.GetProperty("kind").GetString()}:{span.GetProperty("to").GetString()}";
     }
 
-    private static async Task Switch(WorkspaceShellViewModel workspace, Avalonia.Controls.Window window, string name,
+    internal static async Task Switch(WorkspaceShellViewModel workspace, Avalonia.Controls.Window window, string name,
         WorkspacePage page, TextsTab tab)
     {
         var texts = workspace.PageModel<TextsPageModel>();
+        var before = new HashSet<Avalonia.Visual>(Avalonia.VisualTree.VisualExtensions.GetVisualDescendants(window),
+            ReferenceEqualityComparer.Instance as IEqualityComparer<Avalonia.Visual>);
         using var wall = MotifTrace.Begin("harness.click-to-frame");
         wall?.SetTag("view", name);
         if (page == WorkspacePage.Texts && workspace.CurrentPage == WorkspacePage.Texts) texts.Tab = tab;
@@ -206,9 +208,75 @@ private static async Task Switch(WorkspaceShellViewModel workspace, Avalonia.Con
             workspace.SelectedPage = workspace.PageOf(page);
         }
 
-        await WaitForFirstFrame(window, name);
+        var clock = Stopwatch.StartNew();
+        var tick = new Stopwatch();
+        var jobs = new Stopwatch();
+        var iterations = 0;
+        var layoutUpdates = 0;
+        var manager = Avalonia.VisualTree.VisualExtensions.GetLayoutManager(window);
+        EventHandler onLayout = (_, _) => layoutUpdates++;
+        manager.LayoutUpdated += onLayout;
+        while (MotifTrace.CurrentSwitch is not null && clock.Elapsed < TimeSpan.FromSeconds(10))
+        {
+            iterations++;
+            tick.Start();
+            Avalonia.Headless.AvaloniaHeadlessPlatform.ForceRenderTimerTick();
+            tick.Stop();
+            jobs.Start();
+            // Input priority and above, as the real dispatcher runs them; Background work waits for the settle below.
+            Dispatcher.UIThread.RunJobs(DispatcherPriority.Input);
+            jobs.Stop();
+        }
+        manager.LayoutUpdated -= onLayout;
+        using (var split = MotifTrace.Begin("attrib.frame-split"))
+        {
+            split?.SetTag("view", name);
+            split?.SetTag("tick-ms", Math.Round(tick.Elapsed.TotalMilliseconds, 2));
+            split?.SetTag("jobs-ms", Math.Round(jobs.Elapsed.TotalMilliseconds, 2));
+            split?.SetTag("loop-ms", Math.Round(clock.Elapsed.TotalMilliseconds, 2));
+            split?.SetTag("iterations", iterations);
+            split?.SetTag("layout-updated", layoutUpdates);
+        }
+        Assert.True(MotifTrace.CurrentSwitch is null, $"The switch to '{name}' never reached a first frame.");
         wall?.Dispose();
+        using (var tree = MotifTrace.Begin("attrib.tree"))
+        {
+            var all = Avalonia.VisualTree.VisualExtensions.GetVisualDescendants(window).ToList();
+            var visible = all.Where(v => v.IsEffectivelyVisible).ToList();
+            var afterSet = new HashSet<Avalonia.Visual>(all, ReferenceEqualityComparer.Instance as IEqualityComparer<Avalonia.Visual>);
+            var created = all.Where(v => !before.Contains(v)).ToList();
+            tree?.SetTag("view", name);
+            tree?.SetTag("created", created.Count);
+            tree?.SetTag("created-visible", created.Count(v => v.IsEffectivelyVisible));
+            tree?.SetTag("removed", before.Count(v => !afterSet.Contains(v)));
+            tree?.SetTag("created-owner", string.Join(", ", created.GroupBy(Owner)
+                .OrderByDescending(g => g.Count()).Take(12).Select(g => $"{g.Key}={g.Count()}")));
+            tree?.SetTag("created-top", string.Join(", ", created.GroupBy(v => v.GetType().Name)
+                .OrderByDescending(g => g.Count()).Take(30).Select(g => $"{g.Key}={g.Count()}")));
+            tree?.SetTag("visual-all", all.Count);
+            tree?.SetTag("visual-visible", visible.Count);
+            tree?.SetTag("top-visible", string.Join(", ", visible.GroupBy(v => v.GetType().Name)
+                .OrderByDescending(g => g.Count()).Take(14).Select(g => $"{g.Key}={g.Count()}")));
+        }
+        var settle = Stopwatch.StartNew();
         await Quiet(window);
+        using (var after = MotifTrace.Begin("attrib.settle"))
+        {
+            after?.SetTag("view", name);
+            after?.SetTag("quiet-ms", Math.Round(settle.Elapsed.TotalMilliseconds, 1));
+        }
+    }
+
+    private static string Owner(Avalonia.Visual visual)
+    {
+        for (var parent = Avalonia.VisualTree.VisualExtensions.GetVisualParent(visual); parent is not null;
+             parent = Avalonia.VisualTree.VisualExtensions.GetVisualParent(parent))
+        {
+            var type = parent.GetType();
+            if (type.Namespace is { } ns && ns.StartsWith("SIL.Motif.App.Views", StringComparison.Ordinal)
+                && type.Name is not ("MainWindow" or "WorkspaceLayoutHost")) return type.Name;
+        }
+        return "?";
     }
 
     private static Task WaitForFirstFrame(Avalonia.Controls.Window window, string name)
 
@@ -0,0 +1,92 @@
+using SIL.Motif.App;
+using SIL.Motif.App.Services;
+using SIL.Motif.App.ViewModels;
+using SIL.Motif.Commands;
+using SIL.Motif.Commands.Baselines;
+using SIL.Motif.Contract.Ids;
+using SIL.Motif.Contract.Requests;
+using SIL.Motif.Contract.Responses;
+using SIL.Motif.Host;
+using SIL.Motif.Tests.Parser;
+using SIL.Motif.Tests.TestFixtures;
+using Xunit;
+
+namespace SIL.Motif.Tests.App.Walkthrough;
+
+/// <summary>Switches every page and Texts tab over the 3000-word large fixture with the trace on (opt-in, MOTIF_PERF=1).</summary>
+[Collection(LcmCacheTestCollection.Name)]
+[Trait("MotifTestLevel", "System")]
+[Trait("Category", "Perf")]
+public sealed class LargeProjectViewSwitchPerfTests
+{
+    [PerfFact]
+    public void EveryPageAndViewSwitchesOverTheLargeProject()
+    {
+        var path = Environment.GetEnvironmentVariable("MOTIF_PERF_TRACE")
+            ?? Path.Combine(Path.GetTempPath(), "motif-perf-large-trace.jsonl");
+        File.Delete(path);
+        var warmPasses = int.TryParse(Environment.GetEnvironmentVariable("MOTIF_PERF_N"), out var n) && n > 0 ? n : 3;
+        AvaloniaHeadlessFixture.RunUntilComplete(async () =>
+        {
+            using var project = new LargeProjectFixture();
+            var parser = FakeParser.CopyRecordingInvocations(project.ManagedRoot);
+            FakeParser.BehaveBesideExecutable(parser, new
+            {
+                words = project.Words.Select((word, index) => new
+                {
+                    word = word.Form,
+                    outcome = index % 5 == 0 ? "capped" : index % 5 == 1 ? "no-analysis" : "complete",
+                    elapsedMs = 1 + index % 20,
+                    analyses = index % 5 < 2 ? Array.Empty<object>() : new object[]
+                    {
+                        new { morphs = new[] { new
+                        {
+                            form = word.AllomorphId.ToString("D"), msa = word.MsaId.ToString("D"),
+                            inflType = (string?)null, guessedString = (string?)null,
+                        } } },
+                    },
+                }),
+            });
+            var client = RealCommandClient.Create(project.ManagedRoot, parser);
+            Assert.True((await client.CaptureBaselineAsync(new BaselineCaptureRequest(project.FwDataPath), CancellationToken.None)).Succeeded);
+            Assert.True((await client.SetDefaultSelectionAsync(new SetDefaultSelectionRequest(
+                project.FwDataPath, "Large Selection", project.TextIds, []), CancellationToken.None)).Succeeded);
+            Assert.True((await client.SkipSetupAsync(new SkipSetupRequest(project.FwDataPath), CancellationToken.None)).Succeeded);
+            Assert.True((await client.AssessAsync(new AssessRequest(project.FwDataPath),
+                new Progress<AssessmentProgress>(), CancellationToken.None)).Succeeded);
+            var pending = await client.LoadPendingChangesAsync(
+                new PendingChangesRequest(project.FwDataPath, MotifProductVersion.CurrentText), CancellationToken.None);
+            var revision = pending.Value!.Revision;
+            foreach (var word in project.Words.Take(200))
+            {
+                var put = await client.PutPendingChangeAsync(new PutPendingChangeRequest(
+                    project.FwDataPath, MotifProductVersion.CurrentText, revision,
+                    new ChangeIntent(CanonicalId.Mint().Value, "incorrect-spelling",
+                        CanonicalId.FromGuid(word.WordformId).Value, word.Form)), CancellationToken.None);
+                revision = put.Value!.Revision;
+            }
+            using var window = new WalkthroughWindow(project.ManagedRoot, project.FwDataPath, parserPath: parser);
+            window.Show();
+            window.OpenRecentProjectByClick(project.FwDataPath);
+            await window.Workspace.Context.EvidencePublication;
+            window.WaitUntilProjectIsQuiet(TimeSpan.FromSeconds(60), "large project did not finish opening");
+            window.ShowPage(WorkspacePage.Overview);
+            PageScreenshots.Settle(window.Window);
+            // Prime the Texts reader, as a user who has opened Texts once would have.
+            window.ShowPage(WorkspacePage.Texts);
+            window.WaitUntil(() => window.Workspace.PageModel<TextsPageModel>().ResultsInText.Texts.Count == LargeProjectFixture.TextCount,
+                TimeSpan.FromSeconds(60), "the large Texts were not loaded");
+            window.ShowPage(WorkspacePage.Overview);
+            PageScreenshots.Settle(window.Window);
+
+            using var sink = MotifTrace.StartListening(path);
+            for (var pass = 0; pass <= warmPasses; pass++)
+            {
+                MotifTrace.RunLabel = $"{(pass == 0 ? "cold" : "warm")} large";
+                foreach (var (name, page, tab) in PageScreenshots.Views())
+                    await ViewSwitchPerfTests.Switch(window.Workspace, window.Window, name, page, tab);
+            }
+            MotifTrace.RunLabel = null;
+        }, TimeSpan.FromMinutes(20));
+    }
+}
@@ -0,0 +1,30 @@
+# View-switch perf harness and attribution tools
+
+Opt-in measurement of page and Texts-tab switches. Nothing here runs in the normal gate: the facts use
+`PerfFact`, which skips unless `MOTIF_PERF=1`, and they assert no wall-clock figures.
+
+Tests (project `SIL.Motif.Tests.App`):
+
+- `ViewSwitchPerfTests`: sample project, cold then warm, two window sizes.
+- `LargeProjectViewSwitchPerfTests`: the 3000-word large fixture with 200 pending changes and the Texts reader primed.
+
+Run (Linux, from the repo root):
+
+    MOTIF_PERF=1 MOTIF_PERF_N=3 MOTIF_PERF_TRACE=/tmp/large.jsonl \
+      pwsh ./test.ps1 -Project SIL.Motif.Tests.App -Filter LargeProjectViewSwitchPerfTests
+
+`MOTIF_PERF_N` is the warm pass count; `MOTIF_PERF_TRACE` is the JSON-lines trace. Close other test runs first and record
+`uptime` with the numbers, because wall-clock figures move with machine load.
+
+Each switch writes extra spans: `attrib.frame-split` (render ticks versus Input-priority jobs, in ms), `attrib.tree`
+(visuals created and removed, by owning view and by type) and `attrib.settle` (the Background work after the first
+frame). The harness pumps only Input priority and above to the first frame, so work deferred to Background is not
+counted as frame wait.
+
+Summaries (Python 3 standard library only):
+
+    python3 tools/perf-attrib/split.py TRACE "warm large"   # frame split per view, medians
+    python3 tools/perf-attrib/large.py TRACE "warm large"   # loop, created controls, owners, settle per view
+    python3 tools/perf-attrib/agg3.py SPEEDSCOPE.json FILTER N [incl|self]   # needs a speedscope trace of a harness run
+
+`tools/Summarize-MotifTrace.ps1` makes the table for the sample-project run.
@@ -0,0 +1,31 @@
+import json,sys,collections
+d=json.load(open(sys.argv[1])); filt=sys.argv[2]; N=int(sys.argv[3]); mode=sys.argv[4] if len(sys.argv)>4 else 'incl'
+fr=[f['name'] for f in d['shared']['frames']]
+isSw=[('<Switch>d__2.MoveNext' in n) for n in fr]
+isRJ=[('Dispatcher.RunJobs(value class System.Nullable`1<value class Avalonia.Threading.DispatcherPriority>)' in n) for n in fr]
+isQ=[('<Quiet>' in n) for n in fr]
+p=max(d['profiles'],key=lambda p:len(p['events']))
+incl=collections.Counter(); stack=[]; last=None; total=0
+for e in p['events']:
+    t=e['at']
+    if stack and last is not None:
+        li=-1
+        for k in range(len(stack)-1,-1,-1):
+            if isSw[stack[k]]: li=k;break
+        if li>=0:
+            sub=stack[li:]
+            if any(isRJ[i] for i in sub) and not any(isQ[i] for i in sub):
+                dt=t-last; total+=dt
+                if mode=='incl':
+                    for i in set(sub):
+                        if filt in fr[i]: incl[i]+=dt
+                else:
+                    # self: deepest non-CPU frame
+                    j=len(sub)-1
+                    while j>0 and fr[sub[j]] in('CPU_TIME','UNMANAGED_CODE_TIME','?!?'): j-=1
+                    incl[sub[j]]+=dt
+    last=t
+    if e['type']=='O': stack.append(e['frame'])
+    elif stack: stack.pop()
+print('total',round(total))
+for i,v in incl.most_common(N): print(f'{v:8.0f} {fr[i][:165]}')
@@ -0,0 +1,15 @@
+import json,sys,statistics as st,collections
+f=sys.argv[1]; lab=sys.argv[2]
+rows=[json.loads(l) for l in open(f)]
+fs={};tr={};sw=collections.defaultdict(list);q=collections.defaultdict(list)
+fsl=collections.defaultdict(list)
+for r in rows:
+    if r.get('label')!=lab: continue
+    if r['name']=='attrib.frame-split': fsl[r['view']].append(r)
+    if r['name']=='attrib.tree': tr[r['view']]=r
+    if r['name']=='attrib.settle': q[r['view']].append(r['quiet-ms'])
+    if r['name']=='view.switch': sw[r['to']].append(r['ms'])
+print(f"{'view':22}{'switch':>8}{'loop':>8}{'created':>8}{'vis-all':>8}{'quiet':>7}  owner")
+for v,l in fsl.items():
+    t=tr[v]
+    print(f"{v:22}{st.median(x['loop-ms'] for x in l):8.0f}{max(x['loop-ms'] for x in l):8.0f}{t['created']:8}{t['visual-visible']:8}{st.median(q[v]):7.0f}  {t['created-owner'][:110]}")
@@ -0,0 +1,11 @@
+import json,sys,statistics as st,collections
+f=sys.argv[1]; lab=sys.argv[2] if len(sys.argv)>2 else 'warm 1280x800@100'
+rows=[json.loads(l) for l in open(f)]
+d=collections.defaultdict(list)
+for r in rows:
+    if r['name']=='attrib.frame-split' and r.get('label','').startswith(lab.split()[0]) and lab.split()[1] in r.get('label',''):
+        d[r['view']].append(r)
+print(f"{'view':22}{'loop':>8}{'tick':>8}{'jobs':>8}{'iter':>5}{'lu':>5}")
+for v,l in d.items():
+    m=lambda k: st.median(x[k] for x in l)
+    print(f"{v:22}{m('loop-ms'):8.0f}{m('tick-ms'):8.0f}{m('jobs-ms'):8.0f}{m('iterations'):5.0f}{m('layout-updated'):5.0f}")