refactor(render): one group-creation seam, required foliage key field, first-frame wind snap (Campaign VM VM6 review 3)

Narrow re-review of a82959f1: APPROVE, with follow-ups. All items landed.

N2 (structural): (a) extracted the ONE shared InstanceGroup-from-key
construction seam, WbDrawDispatcher.CreateGroupFromKey(key, registration,
frame) — before this there were two near-identical `new InstanceGroup
{ ... }` initializers (GetOrCreateInstanceGroup and GetOrCreatePackedGroup)
that had already drifted once (the round-2 F1 bug). Both routes call it now;
CreateGroupFromKey's own `new()` is the only production InstanceGroup
construction site repo-wide, same precedent as AppendPackedInstance. (b)
GroupKey.FoliageFlags lost its `= 0u` default and moved before CullMode in
the declaration (CullMode keeps its default, C# requires optional params to
trail required ones), so a `new GroupKey(...)` that omits it is a compile
error. Fixed every real construction site the reorder/requirement touched:
the 2 production sites, ToKey (a reconstruction from InstanceGroup the
review didn't count but the reorder broke), and 5 test sites (one more than
the review's "4" — InstanceGroupClearTests had a second, implicit
target-typed `MakeKey` factory the original count missed). Verified by a
full solution build.

N1: added CreateGroupFromKey_CopiesFoliageFlagsFromTheKey
(InstanceGroupClearTests) — a key carrying FoliageFlags 0x2 in, the created
group's FoliageFlags 0x2 out. That test plus N2b's required field are what
actually guard the round-2 F1 blocker; reworded PackedDispatcherOracleTests'
existing test comment to say what IT proves (the classification-to-
BuildIndirectArrays-to-BatchData.flags path), not that it guards the
classifier.

N3: corrected the plan's round-2 paragraph — folding FoliageFlags into the
G2/G3 digest is correct and symmetric, but CompareClassifiedOutput only
runs from RenderScenePViewFrameProductController.BuildAndCompare, which has
no production caller anywhere in src/AcDream.App/, and both of
RenderScenePViewFrameProductTests's own callers construct the controller
without the optional dispatcher argument — so the fold catches nothing
until that oracle is wired to an actual caller.

N4: the plan's F6 note now names both classification caches — the classic
route's EntityClassificationCache.EntityCacheEntry (self-heals per entity
on its own next eviction) and the packed route's
PackedProjectionClassificationEntry/PackedClassifiedBatch.Key
(PackedProjectionClassificationCache.BeginFrame clears its entire cache in
one shot on a RenderSceneGeneration change) — and notes neither mechanism
is keyed to a pack switch specifically.

N5: deleted the now-unused single-generic ComputeEntityHasCutoutSubset<T>
overload; its 4 test call sites now use the two-generic, zero-alloc
overload with an unused int context and a static (_, value) => value
lambda, so there is exactly one ComputeEntityHasCutoutSubset to keep
correct.

A6 (reviewer-filed): ResolveFoliageWind's _windMean/_windGust started at 0
and always eased toward the weather target by clock delta, with no
distinction for a graph's first-ever advance. A pinned clock
(ACDREAM_SKY_PHASE_SECONDS, the offline pixel gate's determinism pin) never
advances between calls, so the wind reached only whatever fraction the
first (1-second-clamped) step produced and sat there forever; live, the
first 10 s after a graph is constructed (pack selection / login) spun up
from dead calm even though the weather already IS what it is. Fixed at the
root: the first advance (_windFrameSerial == -1, the constructor sentinel)
now snaps _windMean/_windGust straight to the target; every later advance
eases over WeatherSystem.TransitionSeconds exactly as before. Added a
SetWindClockSecondsOverrideForTesting seam (_windClockSecondsOverride is no
longer readonly) so a hermetic test can advance the pinned clock by an
exact amount between two resolves without a real-time Thread.Sleep; two new
tests prove the first-advance snap is exact and a second advance still
eases at the normal rate. The three existing indoor/wind-disabled/amplitude
gate tests pass unchanged.

Verify: Release build 0 warnings/0 errors. App hermetic-lane filter
6,046/0 failed. Core.Tests 4,695/0 failed. Full hermetic-filtered solution:
15,274/0 failed across 15 projects.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/AcDream.App.Tests/Rendering/Wb/PackedDispatcherOracleTests.cs

@@ -8,27 +8,23 @@ namespace AcDream.App.Tests.Rendering.Wb;
 public sealed class PackedDispatcherOracleTests
 {
     /// <summary>
-    /// Campaign VM VM6 review fix round 2 (F1 BLOCKER): the production
-    /// packed classifier (WbDrawDispatcher.PackedOracle.cs's
-    /// ClassifyPackedBatches/GetOrCreatePackedGroup) is a private instance
-    /// pipeline reached only through the full RetailPViewPassExecutor →
-    /// DrawPackedProductionRoute route, which needs a real IGpuDevice,
-    /// world-pass scope, mesh manager, and compiled pipelines to construct —
-    /// no test in this suite (or anywhere in the App test project) stands
-    /// one up, so driving ClassifyPackedBatches/GetOrCreatePackedGroup
-    /// directly is not a "cheap test." This proves the two halves of the
-    /// fix that ARE cheaply testable and, chained together, prove the exact
-    /// claim the review asked for: (1) FoliageWindClassification.Classify —
-    /// called with the SAME argument shape ClassifyPackedBatches now uses
+    /// Campaign VM VM6 review fix round 3 (N1): this test does NOT guard
+    /// the packed classifier itself — CreateGroupFromKey's own test
+    /// (InstanceGroupClearTests.CreateGroupFromKey_CopiesFoliageFlagsFromTheKey)
+    /// plus GroupKey.FoliageFlags being a required constructor argument are
+    /// what actually make F1 (the round-2 blocker: the packed classifier's
+    /// InstanceGroup silently carried FoliageFlags == 0) impossible to
+    /// reintroduce. What THIS test proves is the SHARED production step
+    /// downstream of classification: FoliageWindClassification.Classify,
+    /// called with the same argument shape ClassifyPackedBatches uses
     /// (entity.LocalEntityId, exclusion membership, batch.Translucency,
-    /// entity-scoped HasCutoutSubset) — resolves a real procedural-scenery
-    /// entity id (0x8…) to CutoutFoliageFlag (0x2); (2) that flags value,
-    /// carried on an IndirectGroupInput exactly like GetOrCreatePackedGroup
-    /// now carries it on InstanceGroup.FoliageFlags, reaches the literal
-    /// BatchData.flags word through BuildIndirectArrays — the same shared,
-    /// already-tested production step both the classic and packed group
-    /// lists feed into (WbDrawDispatcherIndirectBuilderTests pins bit 0;
-    /// this pins bits 1/2 landing alongside it for a real scenery id).
+    /// entity-scoped HasCutoutSubset), resolves a real procedural-scenery
+    /// entity id (0x8…) to CutoutFoliageFlag (0x2); and a group carrying
+    /// that flags value reaches the literal BatchData.flags word through
+    /// BuildIndirectArrays — the same already-tested production step both
+    /// the classic and packed group lists feed into
+    /// (WbDrawDispatcherIndirectBuilderTests pins bit 0; this pins bits 1/2
+    /// landing alongside it for a real scenery id).
     /// </summary>
     [Fact]
     public void SceneryCutoutEntityClassificationReachesTheBatchDataFlagsWordAsBit0x2()