# Handoff — #171 group-melee interpenetration + facing drift (R5-V3: StickyManager + arrival radii) — 2026-07-04

Fresh session picks up HERE for #171. Worktree `vigorous-joliot-f0c3ad`, branch
`claude/vigorous-joliot-f0c3ad`, tree CLEAN after the #170 close-out
(`4cad626f`). The fix scope below is USER-APPROVED ("Ok I approve",
2026-07-04). Pickup prompt: `docs/research/2026-07-04-171-pickup-prompt.md`.

## Symptom (user report, #170 gate session)

In a pack melee vs the player, acdream monsters end up **partly inside each
other** with **slightly stale facings**, vs retail on the same local ACE.
The #170 chase itself (turn → sustained run → plant → swing) is CLOSED and
gate-passed — do not reopen that machinery.

## Root causes (code-grounded, investigated 2026-07-04)

1. **Sticky melee is a no-op — register TS-39.** ACE arms EVERY melee chase
   with `Sticky | UseFinalHeading | MoveAway | FailWalk`
   (`references/ACE/Source/ACE.Server/WorldObjects/Monster_Navigation.cs:406-419`).
   The retail arrival chain: `MoveToManager::BeginNextNode` (sticky bit set,
   queue empty) reads `SoughtObjectId/Radius/Height` BEFORE `CleanUp` zeroes
   them (that ordering IS already ported — `MoveToManager.cs` ~700-714) and
   calls `PositionManager::StickTo(tlid, radius, height)`; from then on
   `StickyManager::adjust_offset` (0x00555430) runs per tick and holds a
   ~0.3 m edge gap + facing against the moving target. Every
   `MovementManager::PerformMovement` head calls `unstick_from_object` →
   `PositionManager::UnStick` (our `MoveToManager.PerformMovement:414`
   invokes the seam). acdream's `StickTo`/`Unstick` seams are UNBOUND
   (GameWindow `EnsureRemoteMotionBindings` + the player wiring bind
   neither) → attackers complete-and-freeze at stale arrival poses until the
   next wire re-arm. This is the direct cause of BOTH observed symptoms.

2. **Arrival radii are zero.** Retail/ACE arrive EDGE-TO-EDGE: ACE
   `PhysicsObj.MoveToObject` (`references/ACE/…/Physics/PhysicsObj.cs:936-956`)
   reads the TARGET's `PartArray.GetRadius()/GetHeight()` and passes them into
   `MoveToObject_Internal`; the mover's own radius feeds
   `GetCurrentDistance`'s `cylinder_distance` when `UseSpheres` (ACE default
   TRUE, `DistanceToObject` default 0.6). acdream:
   - `GameWindow.EnsureRemoteMotionBindings` binds `getOwnRadius/getOwnHeight
     : () => 0f` — the comment IS the R5-V3 pin ("setup cylsphere radius lands
     with R5-V3");
   - `GameWindow.RouteServerMoveTo` never sets `MovementStruct.Radius/Height`
     (target radii) → 0.
   Net: every attacker closes ~one body-radius deeper than retail → dogpile.

3. **Server-side caveat:** ACE has no monster-vs-monster avoidance; UP
   hard-snaps plant bodies where ACE says (retail hard-snaps identically).
   Some overlap is server-authoritative and visible on retail too —
   **acceptance is retail parity, not zero overlap.**

Ruled out: the between-snap collision sweep. Remotes run the full
`ResolveWithTransition` (GameWindow ~10100) and `CollisionExemption` keeps
creature cylinders collidable for non-viewer movers.

## Approved fix scope (= the R5-V3 slice, roadmap-aligned)

1. **Port `StickyManager` verbatim** (grep `docs/research/named-retail/
   acclient_2013_pseudo_c.txt` for `StickyManager::` first — `StickTo`,
   `UnStick`, `adjust_offset` 0x00555430, `HandleUpdateTarget`; cross-check
   `references/ACE/Source/ACE.Server/Physics/Managers/StickyManager.cs`).
   Groundwork ALREADY in tree (`MoveToMath`): `CylinderDistanceNoZ` (signed —
   the adjust_offset gap math), `GlobalToLocalVec`, `NormalizeCheckSmall` —
   all documented as adjust_offset consumers. `ConstraintManager` (the sibling
   PositionManager member) was ported R5-V1 (TS-35, unarmed — #167 is
   SEPARATE, do not arm it here).
2. **PositionManager**: the facade that owns Sticky + Constraint
   (`references/ACE/…/Managers/PositionManager.cs`). Retail per-tick anchors
   pinned this session from the named decomp:
   - `PositionManager::adjust_offset` called inside
     `CPhysicsObj::UpdatePositionInternal` @0x00512d0e (BEFORE process_hooks);
   - `PositionManager::UseTime` called in `UpdateObjectInternal` @0x005159b3
     (AFTER `CPartArray::HandleMovement`).
   Wire the acdream equivalents at the matching points of the remote tick
   (GameWindow `TickAnimations`) and the player path.
3. **Bind the seams**: `MoveToManager.StickTo` → PositionManager.StickTo;
   `MoveToManager.Unstick` → PositionManager.UnStick — in
   `EnsureRemoteMotionBindings` AND the player wiring (`EnterPlayerModeNow`
   area, ~13128). The TargetManager voyeur fan-out already delivers target
   info; the R5-V2 comment at GameWindow ~4327 says exactly this:
   "PositionManager sticky joins the fan-out in V3" — StickyManager is a
   voyeur consumer in retail (its own HandleUpdateTarget).
4. **Thread real radii**: own radius/height from the entity's Setup (the
   spawn path already reads `setup.Radius`/`setup.Height` for collision
   registration, GameWindow ~4187); target radius/height at the
   `RouteServerMoveTo` MoveToObject branch (resolve the target entity's
   setup — retail reads the TARGET object, not the wire). Sweep BOTH the
   remote and player MoveToManager bindings.
5. **Register bookkeeping (same commit):** retire TS-39; retire/narrow the
   radius pin note; new rows for any adaptation introduced.
6. **Conformance:** extend `RemoteChaseEndToEndHarnessTests` with a sticky
   scenario — arm a sticky MoveToObject, arrive, then MOVE the target
   sideways: assert the follower tracks (gap ≈ stick distance, facing follows)
   and `UnStick` fires on the next PerformMovement head. The harness already
   models the full tick order; add a PositionManager step where retail has it.

## Gotchas

- **Revert-prone area** (remote motion). Follow the workflow: grep named
  decomp FIRST, pseudocode, port verbatim, ACE cross-check, harness, then
  wire. No redesigns; the two prior #170 reverts were redesigns.
- The harness gotcha from #170: any new harness body MUST replicate the live
  `RemoteMotion` construction (`InWorld=true`, `RemoteWeenie`,
  Contact|OnWalkable|Active) or the TS-40 guard strips links and everything
  wedges (`RemoteChaseDrainBisectTests` documents the shape).
- Per-entity probes must print the guid (memory:
  `feedback_probe_identity_attribution` — the #170 misread).
- `StickyManager::adjust_offset` sign semantics: inside the gap the signed
  distance goes NEGATIVE and the per-tick delta inverts (backs off) — ACE
  StickyManager.cs:156, already noted on `MoveToMath.CylinderDistanceNoZ`.
- Do NOT arm ConstraintManager (#167 — two unknown x87 constants).
- Visual gate at the end: pack melee side-by-side vs retail; the user strafes
  around the pack; attackers should reshuffle + keep facing like retail.

## Where things are (quick map)

- `MoveToManager.cs`: `PerformMovement:411` (Unstick head), `BeginNextNode`
  sticky arrival ~700-714, `GetCurrentDistance` (UseSpheres cylinder math).
- `MoveToMath.cs`: `CylinderDistance`, `CylinderDistanceNoZ`,
  `GlobalToLocalVec`, `NormalizeCheckSmall`.
- `GameWindow.cs`: `EnsureRemoteMotionBindings` ~4251 (seams + radius 0f pin),
  `RouteServerMoveTo` ~4457 (MovementStruct — Radius/Height unset), remote
  tick `TickAnimations` (PositionManager wiring points), player wiring ~13128.
- `ConstraintManager.cs` (R5-V1) — PositionManager sibling, reference for the
  port style.
- Register rows: TS-39 (sticky seams), TS-35 (ConstraintManager), TS-41/42
  (#170 rows, adjacent machinery).