Simplify desktop app single-flight readers and trim redundant tests

CLAUDE.md

@@ -143,6 +143,7 @@ dotnet build src/Capacitor.Cli/Capacitor.Cli.csproj
 - Spawning the real `kcap` binary goes through Helpers' `KcapProcess`, which requires a `DaemonStore` and pins it for the child. The assembly-wide `KCAP_DAEMONS_DIR` pin is a path that cannot be created, so a hand-rolled spawn dies with a bare ENOTDIR `IOException` instead of quietly resolving the developer's own daemons directory.
 - Capture console output with `ConsoleOutput.StartCapture()` / `StartErrorCapture()`, never a hand-rolled `Console.SetOut`/`SetError` save-restore — TUnit0055 is an error. Console is process-global, so every caller needs bare `[NotInParallel]`; a group key is not enough.
 - Never assert that an environment variable is *absent* from a built `ProcessStartInfo`: its environment is seeded from the current process, and the repo's own `.envrc` exports several. Assert what the code under test contributed, by comparing against the inherited value.
+- Do not write tests for test-only fakes/mocks, dedicated test files for one-line wrappers/constants already exercised by their callers, or headless XAML smoke tests that only assert `x:Name` lookups, static typography/margin values, or Avalonia layout math. Keep `*SmokeTests` to real view interactions (focus, keyboard/pointer routing, flyouts, accessibility peers) and keep data-projection permutations in ViewModel unit tests.
 
 **Parallelism:** bare `[NotInParallel]` is exclusive against the whole assembly and its tests run last, one at a time; keyed `[NotInParallel("k")]` excludes only tests carrying `k`.
 
@@ -248,6 +249,7 @@ Description: **before writing it, open [.github/PULL_REQUEST_TEMPLATE.md](.githu
   `kcapField` inputs. Fluent `MenuItem` chrome, default `Button` / `ToggleButton` presenters, and
   Fluent accent on a menu or toolbar are out — Fluent paints `PART_ContentPresenter` unless the
   Kcap class restyles it.
+- Reactive and UI-thread discipline: filter `SourceCache.Connect()` streams *before* `.ObserveOn(RxSchedulers.MainThreadScheduler)` so irrelevant cache revisions do not schedule UI-thread work across every open workspace; use `SingleFlightReader<TState, TResult>` for session-keyed single-flight server reads rather than hand-rolling another `ReadLease` state machine; cache template parts (`ScrollViewer`, `TextPresenter`) on `TemplateApplied` instead of walking `GetVisualDescendants()` on keystrokes or layout ticks; and do not run uncached git/disk/hash I/O inside recompute loops or on the UI thread.
 
 ## Dos and donts
 

src/Capacitor.App/Services/AgentDirectory.cs

@@ -159,9 +159,16 @@ public bool Equals(IReadOnlyDictionary<string, string>? x, IReadOnlyDictionary<s
         public int GetHashCode(IReadOnlyDictionary<string, string> obj) => obj.Count;
     }
 
-    RepoIdentity RepoFor(string? repoPath) => repoPath is { Length: > 0 } path
-        ? _repoIdentity.ForLocalRoot(PlatformPaths.Normalize(_resolveLocalRepoRoot(path)))
-        : new RepoIdentity("path:", "No repository");
+    static readonly RepoIdentity NoRepositoryIdentity = new("path:", "No repository");
+    readonly Dictionary<string, RepoIdentity> _repoByPath = new(StringComparer.Ordinal);
+
+    RepoIdentity RepoFor(string? repoPath) {
+        if (repoPath is not { Length: > 0 } path) return NoRepositoryIdentity;
+        if (_repoByPath.TryGetValue(path, out var cached)) return cached;
+        var resolved = _repoIdentity.ForLocalRoot(PlatformPaths.Normalize(_resolveLocalRepoRoot(path)));
+        _repoByPath[path] = resolved;
+        return resolved;
+    }
 
     AgentRow ProjectLocal(AgentStatusDto dto) => AgentRow.FromLocal(dto, RepoFor(dto.RepoPath));
 

src/Capacitor.App/ViewModels/ArtefactsTabViewModel.cs

@@ -2,7 +2,6 @@
 using System.Reactive.Concurrency;
 using System.Security.Cryptography;
 using Avalonia.Collections;
-using Avalonia.Threading;
 using Capacitor.App.Services;
 using Capacitor.Cli.Core;
 using Capacitor.Cli.Core.Plans;
@@ -15,26 +14,15 @@ namespace Capacitor.App.ViewModels;
 /// id, its root, its cancellation and its pending read, a result applies only for the current lease,
 /// and every lease transition happens on the UI thread.
 public sealed class ArtefactsTabViewModel : ReactiveObject {
-    sealed class ReadLease(string sessionId, string? root) {
-        public string SessionId { get; } = sessionId;
-        public string? Root { get; } = root;
-        public CancellationTokenSource Cts { get; } = new();
-        public Task? Pending;
-        public bool RefreshPending;
-        public bool Settled;
-        public bool IsReading => Pending is { IsCompleted: false };
-    }
-
     readonly IPlanArtifactSource? _source;
+    readonly SingleFlightReader<(string SessionId, string? Root), PlanArtifactsRead> _reads;
     readonly PlanActivity _activity;
     readonly TimeProvider _time;
     const long MaxHashedBytes = 4 * 1024 * 1024;
 
     readonly Func<string, Stream?> _openWorkingCopy;
     readonly AvaloniaList<DocumentRow> _documents = [];
-    readonly List<ReadLease> _outstanding = [];
     readonly ITimer _settle;
-    ReadLease? _current;
     bool _tornDown;
     string? _pendingPath;
 
@@ -43,7 +31,7 @@ sealed class ReadLease(string sessionId, string? root) {
     internal bool LastReadFailed { get; private set; }
     public bool HasAny => _documents.Count > 0;
     /// True while a session lease is open and has not yet applied a result — distinct from a settled empty list.
-    public bool IsLoading => _current is { Settled: false };
+    public bool IsLoading => _reads.IsLoading;
     public string SummaryText => _documents.Count == 1 ? "1 document" : $"{_documents.Count} documents";
     /// Right-pane prompt when nothing is open: loading, settled empty, or pick a row.
     public string EmptyReaderNote => IsLoading ? "Loading documents…"
@@ -66,11 +54,20 @@ sealed class ReadLease(string sessionId, string? root) {
     public event Action? OpenRequested;
 
     /// Test-only seam: the current lease's read, or the last one started.
-    internal Task? PendingReadForTesting => _current?.Pending ?? _outstanding.LastOrDefault()?.Pending;
+    internal Task? PendingReadForTesting => _reads.PendingReadForTesting;
 
     public ArtefactsTabViewModel(IPlanArtifactSource? source, PlanActivity activity, TimeProvider time, Func<string, Stream?>? openWorkingCopy = null,
             IUrlOpener? opener = null) {
         _source = source;
+        _reads = new SingleFlightReader<(string SessionId, string? Root), PlanArtifactsRead>(
+            (state, ct) => _source!.ReadAsync(state.SessionId, ct),
+            ex => {
+                Console.Error.WriteLine($"kcap: artefacts tab: {ex.Message}");
+                return PlanArtifactsRead.Of(SessionPlansReadKind.Unreachable);
+            },
+            Apply,
+            "artefacts tab",
+            onSettled: RaiseLoading);
         _activity = activity;
         _time = time;
         _openWorkingCopy = openWorkingCopy ?? OpenFile;
@@ -82,23 +79,24 @@ public ArtefactsTabViewModel(IPlanArtifactSource? source, PlanActivity activity,
 
     public void SwitchSession(string? sessionId, string? root) {
         if (_tornDown || _source is null) return;
-        var old = _current;
-        _current = string.IsNullOrEmpty(sessionId) ? null : new ReadLease(sessionId, root);
-        old?.Cts.Cancel();
         _pendingPath = null;
         LastReadFailed = false;
-        // Raise IsLoading before Clear so observers that combine HasAny || IsLoading see loading
-        // true while HasAny falls — otherwise a stale IsLoading=false hides a sticky tab.
-        RaiseLoading();
-        Clear();
-        if (_current is not null) StartRead(_current);
+        if (string.IsNullOrEmpty(sessionId)) {
+            _reads.ClearCurrent(() => {
+                RaiseLoading();
+                Clear();
+            });
+        } else {
+            _reads.Switch((sessionId, root), () => {
+                RaiseLoading();
+                Clear();
+            });
+        }
     }
 
     /// Reads now, or queues one follow-up behind the read in flight.
     public void Refresh() {
-        if (_tornDown || _current is not { } lease) return;
-        if (lease.IsReading) lease.RefreshPending = true;
-        else StartRead(lease);
+        if (!_tornDown) _reads.Refresh();
     }
 
     public void RequestOpen() => OpenRequested?.Invoke();
@@ -108,7 +106,7 @@ public void Refresh() {
     public bool OpenDocument(string path) {
         var row = Find(path);
         if (row is null) {
-            if (_current is { Settled: false }) _pendingPath = path;
+            if (_reads.HasCurrent && !_reads.IsCurrentSettled) _pendingPath = path;
             else return false;
             if (!HasAny) return false;
             RequestOpen();
@@ -129,7 +127,7 @@ void Select(DocumentRow row) {
     }
 
     DriftState Drift(DocumentRow row) {
-        if (_current?.Root is not { Length: > 0 } root || row.Source != "declared") return DriftState.Unknown;
+        if (_reads.CurrentState.Root is not { Length: > 0 } root || row.Source != "declared") return DriftState.Unknown;
         var relative = row.Path.Replace('\\', '/');
         if (relative.Length == 0 || relative.StartsWith('/') || System.IO.Path.IsPathRooted(relative)
             || (relative.Length >= 2 && char.IsAsciiLetter(relative[0]) && relative[1] == ':')
@@ -151,59 +149,21 @@ void OnPlanWritten() {
         _settle.Change(PlanSectionViewModel.SettleDelay, Timeout.InfiniteTimeSpan);
     }
 
-    void StartRead(ReadLease lease) {
-        lease.RefreshPending = false;
-        lease.Pending = RunReadAsync(lease);
-        _outstanding.Add(lease);
-    }
-
-    async Task RunReadAsync(ReadLease lease) {
-        PlanArtifactsRead? read = null;
-        try {
-            read = await _source!.ReadAsync(lease.SessionId, lease.Cts.Token).ConfigureAwait(false);
-        } catch (OperationCanceledException) {
-        } catch (Exception ex) {
-            Console.Error.WriteLine($"kcap: artefacts tab: {ex.Message}");
-            read = PlanArtifactsRead.Of(SessionPlansReadKind.Unreachable);
-        }
-        try {
-            await Dispatcher.UIThread.InvokeAsync(() => Settle(lease, read));
-        } catch (Exception ex) {
-            Console.Error.WriteLine($"kcap: artefacts tab: {ex.Message}");
-        }
-    }
-
-    void Settle(ReadLease lease, PlanArtifactsRead? read) {
-        _outstanding.Remove(lease);
-        var current = ReferenceEquals(lease, _current) && !_tornDown;
-        if (!current) { lease.Cts.Dispose(); return; }
-        try {
-            if (read is not null) Apply(read);
-        } catch (Exception ex) {
-            Console.Error.WriteLine($"kcap: artefacts tab: {ex.Message}");
-        }
-        if (lease.RefreshPending) StartRead(lease);
-    }
-
     /// Only an unreachable read is worth a retry on the poll: a signed-out or unavailable answer is
     /// what sign-in and the next plan write repair, and polling it would cost a body-carrying request
     /// per workspace per tick for nothing.
     void Apply(PlanArtifactsRead read) {
         LastReadFailed = read.Kind == SessionPlansReadKind.Unreachable;
-        if (_current is { } lease) lease.Settled = true;
-        // Populate (or clear) before RaiseLoading so HasAny || IsLoading never dips to false
-        // between settlement and content — that flicker hides the tab and forces Chat.
         switch (read.Kind) {
             case SessionPlansReadKind.Ready:
                 Show(read.Body?.Artifacts ?? []);
-                break;
+                return;
             case SessionPlansReadKind.Unreachable:
-                break;
+                return;
             default:
                 Clear();
-                break;
+                return;
         }
-        RaiseLoading();
     }
 
     static int KindRank(string kind) => kind switch { "plan" => 0, "spec" => 1, "design" => 2, _ => 3 };
@@ -270,13 +230,6 @@ public async Task TeardownAsync() {
         _settle.Dispose();
         SelectCommand.Dispose();
         OpenLinkCommand.Dispose();
-        var leases = _outstanding.ToArray();
-        foreach (var lease in leases) lease.Cts.Cancel();
-        _current = null;
-        foreach (var lease in leases)
-            if (lease.Pending is { } pending) {
-                try { await pending; } catch (Exception) { }
-            }
-        foreach (var lease in leases) lease.Cts.Dispose();
+        await _reads.TeardownAsync();
     }
 }

src/Capacitor.App/ViewModels/ChatTabViewModel.cs

@@ -423,11 +423,11 @@ internal static string ParticipantNotice(AgentStatusDto dto) {
     /// facts under a Completed status. Identical revisions are not republished.
     static IObservable<ChatSessionInfo> LocalSession(string agentId, IDaemonClientService daemon) =>
         daemon.Agents.Connect()
+            .Filter(dto => dto.Id == agentId)
             .ObserveOn(RxSchedulers.MainThreadScheduler)
             .Scan((ChatSessionInfo?)null, (last, changes) => {
                 var info = last;
                 foreach (var change in changes) {
-                    if (change.Key != agentId) continue;
                     if (change.Reason == ChangeReason.Remove)
                         info = (info ?? ChatSessionInfo.Gone) with {
                             Status = "Completed", StatusLabel = "Done", Ended = true, UsageLimit = null, WaitsOnUser = false,
@@ -725,11 +725,11 @@ void OnSession(ChatSessionInfo info) {
         if (info.FeedKey != _queueKey) {
             _queueKey = info.FeedKey;
             foreach (var foreign in _queuedMessages.Where(q => q.IsForeign).ToList()) _queuedMessages.Remove(foreign);
-            RefreshQueue();
         }
-        if (_openFeed is { } open && info.FeedKey is { } key && key != _feedKey) SwitchFeed(key, open);
+        var switched = _openFeed is { } open && info.FeedKey is { } key && key != _feedKey;
+        if (switched) SwitchFeed(info.FeedKey!, _openFeed!);
         RefreshActivityNote();
-        RefreshQueue();
+        if (!switched) RefreshQueue();
     }
 
     void ApplyUsageLimit(UsageLimitNoticeDto? notice) {
@@ -891,12 +891,17 @@ void Apply(int generation, FeedRead read) {
         Phase = ChatTabPhase.Reading;
         // A send made before the transcript existed has no safe baseline. Its first successful
         // read establishes one; that initial history cannot acknowledge the send.
-        foreach (var queued in Tracked.Where(q => !q.HasBaseline && !q.IsForeign))
+        var rebased = false;
+        foreach (var queued in Tracked.Where(q => !q.HasBaseline && !q.IsForeign)) {
             queued.Rebase(_inputGeneration, read.SnapshotOffset ?? CurrentOffset ?? 0);
-        RefreshQueue();
+            rebased = true;
+        }
+        if (rebased) RefreshQueue();
         if (read.Lines.Count == 0) {
-            SyncPendingCardItems();
-            RefreshActivityNote();
+            if (read.Status == FeedStatus.Reset) {
+                SyncPendingCardItems();
+                RefreshActivityNote();
+            }
             return;
         }