fix(render): S3 chunk 3 round 2 follow-up — the StreamMark pin now fires real StreamMarks

The re-expressed F4(c) pin installed an empty landscape view, so nothing
classified visible, the ordered stream never grew, and no StreamMark
fired: the one behavior round 2 changes was unpinned (review finding).
The test now installs a real full-viewport view and records the trace,
asserting two FLUSH lines ahead of the merged three-cell terrain batch.
The LandCell doc no longer claims an identical submission order; the
resolved image is identical (opaque-vs-opaque order is depth-resolved,
every observable order still flushes first).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

src/AcDream.App/Rendering/Walk/WalkFrameDriver.cs

@@ -302,9 +302,10 @@ internal enum WalkFrameEventKind : byte
     /// ONLY opaque batches, depth test AND write on, no blending, so opaque
     /// terrain and opaque statics resolve identically in either submission
     /// order. A particle turn whose cell has no renderable emitter submits
-    /// nothing and keeps the batch open (fix round 1, F2). The GPU
+    /// nothing and keeps the batch open (fix round 1, F2). The resolved image is therefore identical to replaying each cell
-    /// submission order is therefore identical to replaying each cell
+    /// alone: every event whose GPU order against opaque terrain is
-    /// alone.</summary>
+    /// observable still flushes first (§9.7 F10), and opaque-vs-opaque
+    /// order is depth-resolved.</summary>
     LandCell,
 
     /// <summary><see cref="IWalkFrameLeafRenderer.DrawCellShell"/> —

tests/AcDream.App.Tests/Rendering/Walk/WalkFrameDriverTests.cs

@@ -1530,12 +1530,18 @@ public sealed class WalkFrameDriverTests
         leaf.CellsWithoutEmitters.Add(0xAAAA0001u);
         leaf.CellsWithoutEmitters.Add(0xAAAA0002u);
         var ctx = new TestContext();
-        var driver = new WalkFrameDriver(fx.Dispatcher, leaf, worldData);
+        var driver = new WalkFrameDriver(fx.Dispatcher, leaf, worldData, new RecordingTrace(log));
         IWalkEventSink sink = driver;
 
         using DrawScope draw = fx.BeginDraw();
         driver.BeginFrame(ctx, Matrix4x4.Identity, Vector3.Zero);
-        sink.OnLandscapeViews(new WalkPortalView());
+        // A REAL full-viewport landscape view: with an empty view the classifier
+        // admits nothing, the stream never grows, and no StreamMark ever fires
+        // (the round-2 review caught exactly that vacuity).
+        var landscapeViews = new WalkPortalView();
+        WalkCopyView.AppendFullViewportQuad(
+            landscapeViews, ctx.Rays, ctx.WorldViewpoint, ctx.ViewportWidth, ctx.ViewportHeight);
+        sink.OnLandscapeViews(landscapeViews);
 
         sink.OnLandCellTurn(0xF4180000u, 8, 0);   // landblock A
         sink.OnLandscapeCellTurn(0xAAAA0001u);    // empty particle turn: no growth, no emitters -> no submit, no flush (F2)
@@ -1561,6 +1567,8 @@ public sealed class WalkFrameDriverTests
         Assert.Equal(
             new[]
             {
+                "FLUSH:1:OutdoorStatic",   // 0xAAAA0002's statics: the StreamMark draws its range but does NOT flush the terrain batch (F10)
+                "FLUSH:1:OutdoorStatic",   // 0xBBBB0002's statics: same
                 "LANDCELL:f4180000:8:0,f3180000:8:0,f2180001:8:0",
                 "PARTICLES:bbbb0002",
                 "LANDCELL:f3180000:8:1",
@@ -1572,6 +1580,9 @@ public sealed class WalkFrameDriverTests
             log);
         Assert.DoesNotContain("PARTICLES:aaaa0001", log);
         Assert.DoesNotContain("PARTICLES:aaaa0002", log);
+        // Two genuine StreamMarks fired (the ordered stream grew twice) — the
+        // F10 rule is exercised, not assumed.
+        Assert.Equal(2, log.Count(entry => entry.StartsWith("FLUSH:", StringComparison.Ordinal)));
         Assert.Equal(4, leaf.LandCellBatches.Count);
         Assert.Equal(
             new (uint LandblockId, int SideCellCount, int CellIndex)[]