feat(retail): Commit B — retail-faithful AP cadence + screen-rect picker

Retires divergences flagged in the 2026-05-16 faithfulness audit:

1. AP cadence. Replaces the 1 Hz idle / 10 Hz active flat heartbeat
   with a diff-driven model gated on `Contact && OnWalkable`
   (acclient_2013_pseudo_c.txt:700327 SendPositionEvent). Sends on
   position or cell change while grounded on walkable, plus a 1 sec
   heartbeat; suppressed entirely airborne. PlayerMovementController
   exposes `NotePositionSent(pos, cellId, now)` which GameWindow stamps
   after each AutonomousPosition / MoveToState send — mirrors retail's
   shared `last_sent_position_time` between SendPositionEvent
   (0x006b4770) and SendMovementEvent (0x006b4680). Known divergence
   from retail: ours is per-frame-while-moving, retail's effective rate
   is ~1 Hz during smooth motion (cell/plane checks). Filed as #74,
   blocked by #63 — when #63 lands we revert to retail's narrower gate.

2. Workaround retirement. Removes TinyMargin (0.05 m inside arrival)
   and the AP-flush before re-send (`SendAutonomousPositionNow`). The
   diff-driven cadence makes both obsolete. Close-range turn-first
   deferred Use is kept (it IS retail — ACE Player_Move.cs:66-87
   mirrors retail's CreateMoveToChain pre-callback rotation), renamed
   `OnAutoWalkArrivedSendDeferredAction` to clarify it's a FIRST send.
   `isRetryAfterArrival` parameter dropped.

3. Far-range Use/PickUp retry. Restored — was load-bearing, not the
   "redundant cleanup" the Group 2 audit thought. Issue #63 means ACE
   drops the first Use as too-far without re-polling on subsequent APs;
   the arrival re-send is what makes far-range Use complete. Logs
   include `(queued for arrival re-send pending #63)` to make this
   explicit. Removes when #63 closes.

4. Screen-rect picker. New `AcDream.Core.Selection.ScreenProjection`
   helper shared by `WorldPicker` and `TargetIndicatorPanel`. The
   `Setup.SelectionSphere` projects to a screen-space square (retail
   anchor `SmartBox::GetObjectBoundingBox` 0x00452e20); picker
   hit-tests the mouse pixel against the same rect the indicator draws,
   inflated by 8 px (`TriangleSize`). Guarantees what-you-see is
   what-you-click — including rect corners that were dead zones under
   the old ray-sphere picker. Per-type radius (1.0/1.6/2.0 m) and
   vertical-offset (0.2/0.9/1.0/1.5 m) heuristic lambdas retired;
   `IsTallSceneryGuid` deleted; `EntityHeightFor` trimmed to 1.5 m × scale
   defensive default. No defensive sphere synth — entities without a
   baked `SelectionSphere` are skipped, matching retail's
   `GfxObjUnderSelectionRay` (0x0054c740).

5. Rotation rate run multiplier (Commit A precursor). `TurnRateFor(running)`
   helper applies retail's `run_turn_factor = 1.5f` (PDB-named
   0x007c8914) under HoldKey.Run, matching `apply_run_to_command` at
   0x00527be0 (line 305098). Effective: walking ≈ 90°/s, running ≈ 135°/s.
   Keyboard A/D + ApplyAutoWalkOverlay both use it.

6. Useability gate (Commit A precursor). `IsUseableTarget` corrected to
   `useability != 0` per `ItemUses::IsUseable` at 256455 — ANY non-zero
   passes (USEABLE_NO=1, USEABLE_CONTAINED=8, etc.), not just the
   USEABLE_REMOTE bit. Cross-checked against 4 call sites in retail
   (ItemHolder::UseObject 0x00588a80, DetermineUseResult 0x402697,
   UsingItem 0x367638, disable-button-state 0x198826). Added
   `ProbeUseabilityFallbackEnabled` diagnostic
   (`ACDREAM_PROBE_USEABILITY_FALLBACK=1`) to measure how often the
   creature/BF_DOOR fallback fires for ACE-seed-DB entities with
   null useability.

CLAUDE.md updated with the graceful-shutdown rule for relaunch:
Stop-Process bypasses the logout packet, leaving ACE's session marked
logged-in for ~3+ min. CloseMainWindow() sends WM_CLOSE so the
shutdown hook runs and the logout packet reaches ACE.

Tests: +3 ScreenProjectionTests + 6 WorldPickerRectOverloadTests = +9.
Core.Net 294/294 pass; Core 1073/1081 (8 pre-existing Physics failures
unchanged). Visual-verified 2026-05-16: rotation rate, useability,
screen-rect click area, double-click + R-key + F-key Use/PickUp at
short and long range — dialogue/door/pickup fire on arrival.

Filed follow-ups #70 (triangle apex/size DAT sprite), #71 (picker
Stage B polygon refine), #72 (cdb omega.z probe), #73 (retail-message
sweep pattern), #74 (per-frame AP chattier than retail — blocked by
#63). Old ray-sphere `WorldPicker.Pick(origin, direction, ...)`
overload kept for back-compat; no callers in acdream proper.

Plan: docs/superpowers/plans/2026-05-16-retail-faithfulness-fixes.md

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/AcDream.Core.Tests/Selection/ScreenProjectionTests.cs

@@ -0,0 +1,64 @@
+using System.Numerics;
+using AcDream.Core.Selection;
+
+namespace AcDream.Core.Tests.Selection;
+
+public sealed class ScreenProjectionTests
+{
+    // Standard right-handed perspective + identity view. Sphere centered
+    // at z=-10 in front of camera (System.Numerics
+    // CreatePerspectiveFieldOfView is right-handed; camera at origin
+    // looks down -Z).
+    private static (Matrix4x4 view, Matrix4x4 proj, Vector2 viewport) StdCam()
+    {
+        var view     = Matrix4x4.Identity;
+        var proj     = Matrix4x4.CreatePerspectiveFieldOfView(
+                          MathF.PI * 0.5f /*fovY 90°*/, 800f / 600f, 0.1f, 100f);
+        var viewport = new Vector2(800, 600);
+        return (view, proj, viewport);
+    }
+
+    [Fact]
+    public void TryProject_SphereInFront_ReturnsSquareRect()
+    {
+        var (view, proj, viewport) = StdCam();
+        bool ok = ScreenProjection.TryProjectSphereToScreenRect(
+            new Vector3(0, 0, -10), worldRadius: 1f,
+            view, proj, viewport,
+            out var rMin, out var rMax, out var depth,
+            minSidePixels: 0f);
+
+        Assert.True(ok);
+        Assert.Equal(rMax.X - rMin.X, rMax.Y - rMin.Y, precision: 3);
+        Assert.InRange((rMin.X + rMax.X) * 0.5f, 399f, 401f);
+        Assert.InRange((rMin.Y + rMax.Y) * 0.5f, 299f, 301f);
+        Assert.True(depth > 0f);
+    }
+
+    [Fact]
+    public void TryProject_SphereBehindCamera_ReturnsFalse()
+    {
+        var (view, proj, viewport) = StdCam();
+        bool ok = ScreenProjection.TryProjectSphereToScreenRect(
+            new Vector3(0, 0, +10) /* behind RH camera at origin */,
+            worldRadius: 1f,
+            view, proj, viewport,
+            out _, out _, out _,
+            minSidePixels: 0f);
+        Assert.False(ok);
+    }
+
+    [Fact]
+    public void TryProject_FarSphereClampsToMinSide()
+    {
+        var (view, proj, viewport) = StdCam();
+        bool ok = ScreenProjection.TryProjectSphereToScreenRect(
+            new Vector3(0, 0, -90) /* very far */, worldRadius: 0.01f /* tiny */,
+            view, proj, viewport,
+            out var rMin, out var rMax, out _,
+            minSidePixels: 12f);
+        Assert.True(ok);
+        Assert.True(rMax.X - rMin.X >= 12f);
+        Assert.True(rMax.Y - rMin.Y >= 12f);
+    }
+}