feat(physics): R5-V1 — port PositionManager/Sticky/Constraint + TargetManager (Core, unwired)

The retail movement-manager family the R4 MoveToManager port left as
do-not-invent seams (decomp §9f/§9g). Faithful C# ports of retail's
PositionManager facade + StickyManager + ConstraintManager + the
TargetManager voyeur system, with full conformance tests. NO wiring yet
— purely additive, no behavior change. Wiring (retiring TS-39 sticky +
AP-79 target adapter) is R5-V2/V3.

New Core classes (src/AcDream.Core/Physics/Motion/):
- StickyManager (0x00555400): follow-a-target steering. adjust_offset's
  dense x87 mush decoded via ACE (StickyRadius 0.3, StickyTime 1.0,
  follow speed ×5 / fallback 15) — speed-clamped signed-distance steer +
  bounded turn-to-face; 1 s watchdog; Ok→initialized / non-Ok→teardown.
- ConstraintManager (0x00556090): the server-position rubber-band leash.
  90% IsFullyConstrained jump gate + grounded linear brake taper.
  Structural only — acdream never ARMS it (retail arms from
  SmartBox::HandleReceivedPosition, which acdream lacks, with two x87
  constants BN elided). IsFullyConstrained stays false = TS-35 behavior;
  leash-arming + the unknown constants are a deferred issue.
- PositionManager facade (0x00555160): lazy Sticky/Constraint + fan-out.
- TargetManager (0x0051a370) + TargettedVoyeurInfo: the peer-to-peer
  voyeur subscription system (0.5 s throttle, 10 s staleness,
  send-on-drift-past-radius, dead-reckon GetInterpolatedPosition). A
  faithful superset of the AP-79 adapter — SetTarget subscribes ON the
  target; the target's HandleTargetting pushes updates back.
- IPhysicsObjHost: the CPhysicsObj back-pointer seam (position/velocity/
  radius/contact/GetObjectA + target-tracking fan-out) the App wires per
  entity in V2/V3. MotionDeltaFrame: mutable retail-Frame delta accumulator.

Supporting:
- TargetInfo extended to the full retail 10-field struct (additive
  defaults keep the R4 4-arg call sites compiling).
- MoveToMath: signed CylinderDistanceNoZ, NormalizeCheckSmall,
  GlobalToLocalVec.
- Rename: the misnamed AcDream.Core.Physics.PositionManager (a remote
  anim+interp per-frame combiner, NOT the retail facade) → RemoteMotion
  Combiner, freeing the name and removing the ambiguity that breaks every
  file importing both Physics + Physics.Motion (GameWindow will in V2/V3).

Tests: 42 new conformance cases (Sticky/Constraint/Position facade +
TargetManager incl. the full cross-entity voyeur round-trip). Full suite
4006 green (+2 skipped), no regressions.

Decomp + ACE cross-ref + port plan: docs/research/2026-07-03-r5-managers/.

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

src/AcDream.Core/Physics/Motion/IPhysicsObjHost.cs

@@ -0,0 +1,100 @@
+using System.Numerics;
+
+namespace AcDream.Core.Physics.Motion;
+
+/// <summary>
+/// R5 seam — the acdream stand-in for retail's <c>CPhysicsObj</c> as seen BY
+/// its owned managers. Retail's <c>StickyManager</c> / <c>ConstraintManager</c>
+/// / <c>TargetManager</c> each hold a raw <c>physics_obj</c> pointer and call
+/// back through it (position/velocity/radius accessors, target-tracking
+/// registration, the <c>HandleUpdateTarget</c> fan-out) and — for the voyeur
+/// system — resolve OTHER physics objects via <c>CObjectMaint::GetObjectA</c>
+/// and drive their <c>add_voyeur</c> / <c>receive_target_update</c> /
+/// <c>remove_voyeur</c> entry points. This interface is that back-pointer.
+///
+/// <para>The App layer implements one host per entity (a remote
+/// <c>RemoteMotion</c> or the local player), wiring the accessors to the live
+/// <see cref="PhysicsBody"/> and the <see cref="MoveToManager"/> /
+/// <see cref="PositionManager"/> / <see cref="TargetManager"/> it owns.
+/// <see cref="GetObjectA"/> is backed by the App's live entity table
+/// (<c>_entitiesByServerGuid</c>), giving the voyeur round-trip its
+/// cross-entity delivery path.</para>
+/// </summary>
+public interface IPhysicsObjHost
+{
+    /// <summary>Retail <c>physics_obj-&gt;id</c> — this object's guid.</summary>
+    uint Id { get; }
+
+    /// <summary>Retail <c>physics_obj-&gt;m_position</c> — world-space cell +
+    /// frame (acdream seams carry WORLD space; see the MoveToManager binding
+    /// note).</summary>
+    Position Position { get; }
+
+    /// <summary>Retail <c>CPhysicsObj::get_velocity</c>.</summary>
+    Vector3 Velocity { get; }
+
+    /// <summary>Retail <c>CPhysicsObj::GetRadius</c> — the mover's cylinder
+    /// radius.</summary>
+    float Radius { get; }
+
+    /// <summary>Retail <c>physics_obj-&gt;transient_state &amp; 1</c> — the
+    /// CONTACT bit (ConstraintManager's grounded gate).</summary>
+    bool InContact { get; }
+
+    /// <summary>Retail <c>CPhysicsObj::get_minterp()-&gt;get_max_speed()</c> —
+    /// the mover's max locomotion speed, or <c>null</c> if it has no motion
+    /// interpreter yet (StickyManager falls back to a 15.0 constant).</summary>
+    float? MinterpMaxSpeed { get; }
+
+    /// <summary>Retail <c>Timer::cur_time</c> — the wall/game clock (seconds).
+    /// Drives the sticky 1 s timeout and target 10 s staleness deadlines.</summary>
+    double CurTime { get; }
+
+    /// <summary>Retail <c>PhysicsTimer::curr_time</c> — the physics-tick clock
+    /// (seconds). Drives <c>TargetManager::HandleTargetting</c>'s 0.5 s
+    /// throttle. Retail uses a DIFFERENT clock here than <see cref="CurTime"/>;
+    /// acdream may bind both to the same source.</summary>
+    double PhysicsTimerTime { get; }
+
+    /// <summary>Retail <c>CObjectMaint::GetObjectA(id)</c> — resolve another
+    /// physics object by guid, or <c>null</c> if not currently known/visible.
+    /// The cross-entity seam for the voyeur round-trip and sticky live-target
+    /// resolve.</summary>
+    IPhysicsObjHost? GetObjectA(uint id);
+
+    /// <summary>Retail <c>CPhysicsObj::HandleUpdateTarget</c> — fans a
+    /// <see cref="TargetInfo"/> to this host's <see cref="MoveToManager"/>
+    /// (move-to steering) AND <see cref="PositionManager"/> (sticky follow).
+    /// Called from <see cref="TargetManager.ReceiveUpdate"/> and the timeout
+    /// path.</summary>
+    void HandleUpdateTarget(TargetInfo info);
+
+    /// <summary>Retail <c>CPhysicsObj::interrupt_current_movement</c> →
+    /// <c>MovementManager::CancelMoveTo(0x36)</c>.</summary>
+    void InterruptCurrentMovement();
+
+    /// <summary>Retail <c>CPhysicsObj::set_target(ctx, objId, radius,
+    /// quantum)</c> → <see cref="TargetManager.SetTarget"/> (lazily creating
+    /// the TargetManager). Called by <c>StickyManager::StickTo</c> and
+    /// <c>MoveToManager</c>'s object-move entry points.</summary>
+    void SetTarget(uint contextId, uint objectId, float radius, double quantum);
+
+    /// <summary>Retail <c>CPhysicsObj::clear_target</c> →
+    /// <see cref="TargetManager.ClearTarget"/>.</summary>
+    void ClearTarget();
+
+    /// <summary>Retail <c>CPhysicsObj::receive_target_update</c> →
+    /// <see cref="TargetManager.ReceiveUpdate"/>. The inbound side a SENDER's
+    /// <c>SendVoyeurUpdate</c> tail-calls on the watcher.</summary>
+    void ReceiveTargetUpdate(TargetInfo info);
+
+    /// <summary>Retail <c>CPhysicsObj::add_voyeur(id, radius, quantum)</c> →
+    /// <see cref="TargetManager.AddVoyeur"/> (lazily creating the
+    /// TargetManager). Called on the TARGET when a watcher subscribes.</summary>
+    void AddVoyeur(uint watcherId, float radius, double quantum);
+
+    /// <summary>Retail <c>CPhysicsObj::remove_voyeur(id)</c> →
+    /// <see cref="TargetManager.RemoveVoyeur"/>. Called on the TARGET when a
+    /// watcher unsubscribes.</summary>
+    void RemoveVoyeur(uint watcherId);
+}