feat(A): wire SweepEye to the verbatim update_viewer (start-cell + fallbacks)

Complete Render Residual A's faithful port: PhysicsCameraCollisionProbe.SweepEye
now mirrors SmartBox::update_viewer (acclient_2013_pseudo_c.txt:92761) end-to-end:

- Start cell (pc:92824-92844): indoor (>=0x100) seats the sweep at the head-PIVOT
  via PhysicsEngine.AdjustPosition (the cellar-lip case — feet in the low connector,
  head up at floor level); outdoor keeps the player cell.
- Sweep pivot -> sought-eye from the seated start cell (unchanged 0x5c viewer flags).
- Success (pc:92870): set_viewer(curr_pos), viewer_cell = curr_cell.
- Fallback 1 (pc:92878): AdjustPosition(sought_eye).
- Fallback 2 / no-cell (pc:92775, 92886): snap to player, viewer_cell = null. This
  also makes cellId==0 faithful (was returning the desired eye; retail snaps to
  player_pos) and adds the playerPos arg to ICameraCollisionProbe.SweepEye.

Supporting: ResolveResult.Ok surfaces FindTransitionalPosition's return (retail
find_valid_position != 0, pc:273898) so SweepEye knows when to fall back.

TDD: 11 new tests (FindVisibleChildCell 4, AdjustPosition 3, ResolveResult.Ok 2,
SweepEye orchestration 2). The seating test's RED proved the sweep does NOT auto-
advance feet->room, so the pivot-seated start cell is genuinely decisive. Core
1326 pass / 4 documented-fail / 1 skip; App 179 pass / 0 fail. No regression.

Per the live-capture finding, the visible payoff is the cellar-corner (point 3);
the cottage-room bluish void stays for residual C. Spec:
docs/superpowers/specs/2026-06-05-residual-a-camera-collision-design.md.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/AcDream.Core.Tests/Physics/ResolveResultOkTests.cs

@@ -0,0 +1,45 @@
+using System.Numerics;
+using AcDream.Core.Physics;
+using Xunit;
+
+namespace AcDream.Core.Tests.Physics;
+
+/// <summary>
+/// Render Residual A — <see cref="ResolveResult.Ok"/> surfaces the
+/// <c>FindTransitionalPosition</c> return (retail <c>find_valid_position != 0</c>,
+/// pc:273898) so the camera <c>SweepEye</c> can trigger <c>SmartBox::update_viewer</c>'s
+/// fallbacks when the sweep fails. Default <c>true</c> keeps every existing caller
+/// (which never reads it) unaffected.
+/// </summary>
+public class ResolveResultOkTests
+{
+    [Fact]
+    public void NoStartCell_ReportsNotOk()
+    {
+        var engine = new PhysicsEngine();
+
+        // cellId == 0 → FindTransitionalPosition returns false at its first guard
+        // (TransitionTypes.cs:665) → the sweep did not find a valid position.
+        var r = engine.ResolveWithTransition(
+            currentPos: Vector3.Zero, targetPos: new Vector3(1f, 0f, 0f), cellId: 0u,
+            sphereRadius: 0.3f, sphereHeight: 0f, stepUpHeight: 0f, stepDownHeight: 0f,
+            isOnGround: false);
+
+        Assert.False(r.Ok);
+    }
+
+    [Fact]
+    public void ZeroMovementValidCell_ReportsOk()
+    {
+        var engine = new PhysicsEngine();
+
+        // Zero offset with a non-zero start cell → FindTransitionalPosition's
+        // zero-step path returns true (TransitionTypes.cs:718-723), no geometry needed.
+        var r = engine.ResolveWithTransition(
+            currentPos: new Vector3(5f, 5f, 5f), targetPos: new Vector3(5f, 5f, 5f), cellId: 0xA9B40001u,
+            sphereRadius: 0.3f, sphereHeight: 0f, stepUpHeight: 0f, stepDownHeight: 0f,
+            isOnGround: false);
+
+        Assert.True(r.Ok);
+    }
+}