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>

src/AcDream.Core/Selection/WorldPicker.cs

@@ -158,4 +158,91 @@ public static class WorldPicker
         }
         return bestGuid;
     }
+
+    /// <summary>
+    /// 2026-05-16. Screen-space rect-hit-test picker overload. Each
+    /// candidate's world-space sphere (via <paramref name="sphereForEntity"/>)
+    /// projects to a screen-space rectangle through
+    /// <see cref="ScreenProjection.TryProjectSphereToScreenRect"/>. The
+    /// rect is inflated by <paramref name="inflatePixels"/> on every side
+    /// (matches the indicator's <c>TriangleSize</c> outer brackets) and
+    /// hit-tested against the mouse pixel. Among rects that contain the
+    /// mouse, the entity with the nearest camera-space depth wins.
+    ///
+    /// <para>
+    /// Why screen-space instead of world-space ray-sphere: the indicator
+    /// draws a screen-space RECT. A world-space sphere projects to a
+    /// screen CIRCLE inscribed in that rect — leaving the four rect
+    /// corners as click dead zones. Per user feedback 2026-05-16, the
+    /// click area must match the visible indicator extent exactly. By
+    /// sharing the <see cref="ScreenProjection"/> helper with
+    /// <c>TargetIndicatorPanel</c>, the click rect and the drawn rect
+    /// cannot drift.
+    /// </para>
+    ///
+    /// <para>
+    /// Resolver returning <c>null</c> skips the candidate (matches retail
+    /// "no Setup → not pickable" behavior). Entities with
+    /// <c>ServerGuid == 0</c> (atlas-tier scenery) and the player's own
+    /// guid are also skipped.
+    /// </para>
+    ///
+    /// <para>
+    /// Stage A of the picker port. Stage B (polygon refine via
+    /// <c>CPolygon::polygon_hits_ray</c> 0x0054c889) remains deferred
+    /// per issue #71 — only needed if visual testing surfaces a Stage A
+    /// over-pick on entities whose visible mesh is well inside the
+    /// indicator rect.
+    /// </para>
+    /// </summary>
+    /// <param name="inflatePixels">Pixel inflate on each side of the
+    /// projected rect. Pass the indicator's <c>TriangleSize</c> (8 px)
+    /// so the click area extends to where the visible bracket corners
+    /// sit — the user perceives the inflated rect as the clickable area.</param>
+    public static uint? Pick(
+        float mouseX, float mouseY,
+        Matrix4x4 view,
+        Matrix4x4 projection,
+        Vector2 viewport,
+        IEnumerable<WorldEntity> candidates,
+        uint skipServerGuid,
+        Func<WorldEntity, (Vector3 CenterWorld, float Radius)?> sphereForEntity,
+        float inflatePixels = 8f)
+    {
+        uint? bestGuid  = null;
+        float bestDepth = float.PositiveInfinity;
+
+        foreach (var entity in candidates)
+        {
+            if (entity.ServerGuid == 0u)             continue;
+            if (entity.ServerGuid == skipServerGuid) continue;
+
+            var sphere = sphereForEntity(entity);
+            if (sphere is null) continue;
+            var (center, radius) = sphere.Value;
+            if (radius <= 0f) continue;
+
+            if (!ScreenProjection.TryProjectSphereToScreenRect(
+                    center, radius, view, projection, viewport,
+                    out var rMin, out var rMax, out var depth))
+                continue;
+
+            // Inflate by inflatePixels on each side — extend hit area to
+            // where the indicator brackets sit.
+            float minX = rMin.X - inflatePixels;
+            float minY = rMin.Y - inflatePixels;
+            float maxX = rMax.X + inflatePixels;
+            float maxY = rMax.Y + inflatePixels;
+
+            if (mouseX < minX || mouseX > maxX) continue;
+            if (mouseY < minY || mouseY > maxY) continue;
+
+            if (depth < bestDepth)
+            {
+                bestDepth = depth;
+                bestGuid  = entity.ServerGuid;
+            }
+        }
+        return bestGuid;
+    }
 }