diff --git a/src/AcDream.App/Composition/SessionPlayerComposition.cs b/src/AcDream.App/Composition/SessionPlayerComposition.cs
index 1baac0b7..2af1a65b 100644
--- a/src/AcDream.App/Composition/SessionPlayerComposition.cs
+++ b/src/AcDream.App/Composition/SessionPlayerComposition.cs
@@ -425,7 +425,8 @@ internal sealed class SessionPlayerCompositionPhase
             spawnClaimClassifier.IsUnhydratable,
             worldQuiescence,
             streaming,
-            revealRenderResources);
+            revealRenderResources,
+            () => live.WorldState.LoadedLandblockCount);
         Fault(SessionPlayerCompositionPoint.WorldRevealCreated);
 
         return CompleteSessionPlayer(
diff --git a/src/AcDream.App/Streaming/GpuWorldState.cs b/src/AcDream.App/Streaming/GpuWorldState.cs
index 5504862c..ce8cb764 100644
--- a/src/AcDream.App/Streaming/GpuWorldState.cs
+++ b/src/AcDream.App/Streaming/GpuWorldState.cs
@@ -198,6 +198,10 @@ public sealed class GpuWorldState : ILiveEntitySpatialQuery
     /// that need to enumerate entities before the landblock is dropped
     /// (e.g. unregistering dynamic lights on a RemoveLandblock).
     /// </summary>
+    /// <summary>Resident landblock count — reveal-timing probe progress
+    /// lines only (<see cref="RevealTimingProbe"/>).</summary>
+    public int LoadedLandblockCount => _loaded.Count;
+
     public bool TryGetLandblock(uint landblockId, out LoadedLandblock? lb)
     {
         if (_loaded.TryGetValue(landblockId, out var found))
diff --git a/src/AcDream.App/Streaming/RevealTimingProbe.cs b/src/AcDream.App/Streaming/RevealTimingProbe.cs
new file mode 100644
index 00000000..2b2d9f7b
--- /dev/null
+++ b/src/AcDream.App/Streaming/RevealTimingProbe.cs
@@ -0,0 +1,155 @@
+using System.Diagnostics;
+using AcDream.Runtime;
+
+namespace AcDream.App.Streaming;
+
+/// <summary>
+/// <c>ACDREAM_PROBE_REVEAL_TIMING=1</c> (see
+/// <see cref="StreamingDiagnostics.ProbeRevealTiming"/>): wall-clock
+/// attribution of one login/portal hold. Emits <c>[reveal-timing]</c> lines:
+///
+/// <list type="bullet">
+/// <item><c>event=begin</c> — the hold starts, with the required window and
+/// its landblock count.</item>
+/// <item><c>event=render-ready / composites-ready / collision-ready /
+/// gate-ready / materialized</c> — first-true edges with elapsed ms. The
+/// readiness barrier OBSERVES the dimensions serially (composites are only
+/// evaluated once render is ready, collision once both are), so each edge's
+/// delta over the previous one is that dimension's observed TAIL, not its
+/// total concurrent cost — the progress lines carry the concurrency
+/// shape.</item>
+/// <item>1 Hz progress — elapsed, the three flags, and the resident
+/// landblock count, so a budget-paced linear drip is visually obvious in the
+/// log.</item>
+/// <item><c>SUMMARY</c> once at the viewport reveal — the per-edge
+/// timeline on one line.</item>
+/// </list>
+///
+/// Diagnostic-only: never constructed unless the probe env is set, changes
+/// no behavior, and costs one branch per <c>Evaluate</c> poll otherwise.
+/// </summary>
+internal sealed class RevealTimingProbe
+{
+    private readonly Func<int>? _loadedLandblockCount;
+    private readonly Stopwatch _clock = new();
+    private long _generation;
+    private string _kind = "";
+    private int _windowLandblocks;
+    private bool _render;
+    private bool _composites;
+    private bool _collision;
+    private bool _gateReady;
+    private bool _materialized;
+    private bool _summarized;
+    private long _renderMs = -1;
+    private long _compositesMs = -1;
+    private long _collisionMs = -1;
+    private long _gateReadyMs = -1;
+    private long _materializedMs = -1;
+    private long _lastProgressMs;
+
+    public RevealTimingProbe(Func<int>? loadedLandblockCount) =>
+        _loadedLandblockCount = loadedLandblockCount;
+
+    public void Begin(
+        string kind,
+        long generation,
+        uint destinationCell,
+        in StreamingRevealWindow window)
+    {
+        _generation = generation;
+        _kind = kind;
+        int side = window.FarRadius * 2 + 1;
+        _windowLandblocks = side * side;
+        _render = false;
+        _composites = false;
+        _collision = false;
+        _gateReady = false;
+        _materialized = false;
+        _summarized = false;
+        _renderMs = -1;
+        _compositesMs = -1;
+        _collisionMs = -1;
+        _gateReadyMs = -1;
+        _materializedMs = -1;
+        _lastProgressMs = 0;
+        _clock.Restart();
+        Console.WriteLine(
+            $"[reveal-timing] event=begin kind={kind} gen={generation} "
+            + $"cell=0x{destinationCell:X8} window={window.NearRadius}/"
+            + $"{window.FarRadius} landblocks={_windowLandblocks} "
+            + $"loaded={_loadedLandblockCount?.Invoke() ?? -1}");
+    }
+
+    public void Observe(
+        in WorldRevealReadinessSnapshot readiness,
+        in RuntimePortalSnapshot portal)
+    {
+        if (_generation == 0 || portal.Generation != _generation)
+            return;
+
+        long elapsed = _clock.ElapsedMilliseconds;
+        if (!_render && readiness.IsRenderNeighborhoodReady)
+        {
+            _render = true;
+            _renderMs = elapsed;
+            Edge("render-ready", elapsed);
+        }
+        if (!_composites && readiness.AreCompositeTexturesReady)
+        {
+            _composites = true;
+            _compositesMs = elapsed;
+            Edge("composites-ready", elapsed);
+        }
+        if (!_collision && readiness.IsCollisionReady)
+        {
+            _collision = true;
+            _collisionMs = elapsed;
+            Edge("collision-ready", elapsed);
+        }
+        if (!_gateReady && readiness.IsReady)
+        {
+            _gateReady = true;
+            _gateReadyMs = elapsed;
+            Edge("gate-ready", elapsed);
+        }
+        if (!_materialized && portal.Materialized)
+        {
+            _materialized = true;
+            _materializedMs = elapsed;
+            Edge("materialized", elapsed);
+        }
+
+        if (!_summarized && portal.WorldViewportObserved)
+        {
+            _summarized = true;
+            Console.WriteLine(
+                $"[reveal-timing] SUMMARY kind={_kind} gen={_generation} "
+                + $"totalMs={elapsed} renderMs={_renderMs} "
+                + $"compositesMs={_compositesMs} collisionMs={_collisionMs} "
+                + $"gateReadyMs={_gateReadyMs} "
+                + $"materializedMs={_materializedMs} "
+                + $"landblocks={_windowLandblocks}");
+            return;
+        }
+
+        if (!_summarized && elapsed - _lastProgressMs >= 1000)
+        {
+            _lastProgressMs = elapsed;
+            Console.WriteLine(
+                $"[reveal-timing] elapsedMs={elapsed} "
+                + $"render={(_render ? 1 : 0)} "
+                + $"composites={(_composites ? 1 : 0)} "
+                + $"collision={(_collision ? 1 : 0)} "
+                + $"loaded={_loadedLandblockCount?.Invoke() ?? -1}"
+                + $"/{_windowLandblocks}");
+        }
+    }
+
+    private void Edge(string name, long elapsed) =>
+        Console.WriteLine(
+            $"[reveal-timing] event={name} kind={_kind} gen={_generation} "
+            + $"elapsedMs={elapsed} "
+            + $"loaded={_loadedLandblockCount?.Invoke() ?? -1}"
+            + $"/{_windowLandblocks}");
+}
diff --git a/src/AcDream.App/Streaming/StreamingDiagnostics.cs b/src/AcDream.App/Streaming/StreamingDiagnostics.cs
index d40471f4..5102b484 100644
--- a/src/AcDream.App/Streaming/StreamingDiagnostics.cs
+++ b/src/AcDream.App/Streaming/StreamingDiagnostics.cs
@@ -51,6 +51,19 @@ internal static class StreamingDiagnostics
             far);
     }
 
+    /// <summary>
+    /// Login-load measurement probe (2026-08-17): when set, the reveal
+    /// coordinator emits a <c>[reveal-timing]</c> wall-clock timeline for
+    /// every login/portal hold — per-dimension first-ready edges
+    /// (render neighborhood, composite textures, collision), 1 Hz progress
+    /// with the resident-landblock count, and one summary line at the
+    /// viewport reveal — so optimization targets the measured dominant
+    /// phase instead of a guess. Diagnostic-only: not a user setting, not
+    /// persisted, no behavior change.
+    /// </summary>
+    public static bool ProbeRevealTiming { get; } =
+        Environment.GetEnvironmentVariable("ACDREAM_PROBE_REVEAL_TIMING") == "1";
+
     /// <summary>
     /// The floor is 1, not 0. An outdoor destination's acknowledgement must
     /// carry <c>RequiredRenderRadius &gt;= 1</c> or
diff --git a/src/AcDream.App/Streaming/WorldRevealCoordinator.cs b/src/AcDream.App/Streaming/WorldRevealCoordinator.cs
index d8ee6b44..8e74ab1e 100644
--- a/src/AcDream.App/Streaming/WorldRevealCoordinator.cs
+++ b/src/AcDream.App/Streaming/WorldRevealCoordinator.cs
@@ -68,6 +68,7 @@ internal sealed class WorldRevealCoordinator
     private readonly IWorldRevealStreamingScheduler? _streaming;
     private readonly IWorldRevealRenderResourceScheduler? _renderResources;
     private readonly List<HostProjection> _hostProjections = [];
+    private readonly RevealTimingProbe? _timing;
     private bool _hostRetryActive;
     private bool _hostRetryRequested;
 
@@ -83,7 +84,8 @@ internal sealed class WorldRevealCoordinator
         Func<uint, bool> isSpawnClaimUnhydratable,
         WorldGenerationQuiescence? quiescence = null,
         IWorldRevealStreamingScheduler? streaming = null,
-        IWorldRevealRenderResourceScheduler? renderResources = null)
+        IWorldRevealRenderResourceScheduler? renderResources = null,
+        Func<int>? loadedLandblockCount = null)
     {
         _transit = transit ?? throw new ArgumentNullException(nameof(transit));
         _readiness = new WorldRevealReadinessBarrier(
@@ -98,6 +100,8 @@ internal sealed class WorldRevealCoordinator
         _quiescence = quiescence;
         _streaming = streaming;
         _renderResources = renderResources;
+        if (StreamingDiagnostics.ProbeRevealTiming)
+            _timing = new RevealTimingProbe(loadedLandblockCount);
     }
 
     public RuntimePortalSnapshot Snapshot => _transit.Snapshot;
@@ -117,6 +121,11 @@ internal sealed class WorldRevealCoordinator
             _quiescence?.CaptureBegin() ?? default;
         _readiness.Begin();
         long generation = _transit.BeginLoginReveal(destinationCell);
+        _timing?.Begin(
+            "login",
+            generation,
+            destinationCell,
+            _readiness.RequiredWindow(destinationCell));
         BeginHostLifetime(
             generation,
             destinationCell,
@@ -151,6 +160,11 @@ internal sealed class WorldRevealCoordinator
         }
 
         _readiness.Begin();
+        _timing?.Begin(
+            "portal",
+            generation,
+            destinationCell,
+            _readiness.RequiredWindow(destinationCell));
         BeginHostLifetime(
             generation,
             destinationCell,
@@ -195,6 +209,7 @@ internal sealed class WorldRevealCoordinator
         WorldRevealReadinessSnapshot snapshot = _readiness.Evaluate(destinationCell);
         ReconcileDestinationReservationRadius(snapshot);
         RuntimePortalSnapshot portal = _transit.Snapshot;
+        _timing?.Observe(snapshot, portal);
         if (portal.Generation != 0)
         {
             _transit.AcknowledgeDestinationReadiness(