# Phase B.6 — Suppress outbound `MoveToState` during inbound MoveToObject auto-walk

**Date:** 2026-05-16
**Closes:** [#63](../../ISSUES.md) (server-initiated auto-walk not honored — the half about ACE's `MoveToChain` callback never firing), [#74](../../ISSUES.md) (AP cadence chattier than retail)
**Milestone:** M1 — Walkable + clickable world

## Goal

Make ACE's server-side `MoveToChain` callback fire the Use action on arrival, eliminating the client-side retry workaround that today's `feat(retail): Commit B` (`b5da17d`) restored as an issue-#63 mitigation.

## Background

When the player double-clicks an NPC across the room in our current build:

1. We send `Use(guid)` wire packet immediately at click.
2. ACE: player not in `WithinUseRadius` → server-side `CreateMoveToChain(item, (success) => TryUseItem(item, success))` ([`Player_Use.cs:205`](../../../references/ACE/Source/ACE.Server/WorldObjects/Player_Use.cs)).
3. ACE broadcasts `UpdateMotion` with `MovementType=6` (MoveToObject) targeting our player.
4. Our client honors it via `BeginServerAutoWalk(...)` at [`GameWindow.cs:3389-3414`](../../../src/AcDream.App/Rendering/GameWindow.cs).
5. The auto-walk overlay at [`PlayerMovementController.ApplyAutoWalkOverlay`](../../../src/AcDream.App/Input/PlayerMovementController.cs) synthesizes `input.Forward = true, input.Run = true` (line 611-619) so the rest of `Update` runs as if the user pressed W.
6. **Bug:** the rest of `Update` computes `MotionStateChanged = true` and the outbound wire layer at [`GameWindow.cs:6410-6445`](../../../src/AcDream.App/Rendering/GameWindow.cs) builds and sends a `MoveToState` packet with `forwardCommand=RunForward, holdKey=Run`.
7. ACE reads that as **user took manual control** and cancels its own `MoveToChain` — the `TryUseItem` callback never fires.
8. We've worked around this by sending `Use` a second time on local-arrival (`_pendingPostArrivalAction` in [`GameWindow.SendUse` far-range path](../../../src/AcDream.App/Rendering/GameWindow.cs)). ACE accepts the second Use because we're now in range. **This is what we're retiring.**

The retail client and holtburger's Rust client don't have this bug: neither synthesizes player-input MoveToState during inbound MoveToObject. Their auto-walk is body-level only; ACE's chain runs uninterrupted; the callback fires on arrival.

### Retail anchor

- ACE `Player_Use.cs:205` — `CreateMoveToChain(item, (success) => TryUseItem(item, success))`.
- ACE `Player_Move.cs:150` — chain polls and fires `callback(true)` when within use radius.
- Holtburger [`simulation.rs:178-206`](../../../references/holtburger/crates/holtburger-core/src/client/simulation.rs) — `MoveToObject` handler returns `Ok(Vec::new())`, no outbound packets in response. No retry mechanism anywhere in its codebase.

## Design

Single-flag suppression of the outbound `MoveToState` send while a server-initiated auto-walk is active. The body keeps walking locally (synth still drives the animation cycle + per-frame position update), `AutonomousPosition` keeps flowing (so ACE's `WithinUseRadius` poll sees us approach), but the misleading "user is RunForward" packet is silenced.

### Wire-level changes

**File: [`src/AcDream.App/Input/PlayerMovementController.cs`](../../../src/AcDream.App/Input/PlayerMovementController.cs)**

No new field needed — [`IsServerAutoWalking`](../../../src/AcDream.App/Input/PlayerMovementController.cs:273) already exists, added by B.6 slice 2 (2026-05-14) for this purpose. Backs onto private `_autoWalkActive` (line 254). Set true by `BeginServerAutoWalk`, false by `EndServerAutoWalk`. User-input cancellation at line 478-482 already clears the flag, so manual takeover transitions correctly to "user is in control, send MoveToState normally."

**File: [`src/AcDream.App/Rendering/GameWindow.cs`](../../../src/AcDream.App/Rendering/GameWindow.cs)**

Guard the `MoveToState.Build` block at lines 6410-6445 with a second condition:

```csharp
if (result.MotionStateChanged && !_playerController.IsServerAutoWalking)
{
    // ... existing MoveToState build + SendGameAction ...
}
```

No other path needs adjustment; the AutonomousPosition path remains unchanged (heartbeat-driven, gated on `Contact && OnWalkable`).

Single-clause add; `IsServerAutoWalking` already documented at line 267-273 as the predicate for "the next Update synthesizes Forward+Run."

### Workaround retirement

After the wire fix is verified, the following Commit B safeguards are deleted:

1. **Far-range Use retry.** In [`GameWindow.SendUse`](../../../src/AcDream.App/Rendering/GameWindow.cs) (~line 9201-9204), remove the `_pendingPostArrivalAction = (guid, false);` assignment from the far-range path and rewrite the comment block to say "ACE auto-fires Use via MoveToChain callback; client sends Use exactly once."

2. **Far-range PickUp retry.** Same shape in [`GameWindow.SendPickUp`](../../../src/AcDream.App/Rendering/GameWindow.cs) (~line 9265).

3. **Log strings.** Drop `(queued for arrival re-send pending #63)` from the same paths.

4. **AP cadence revert.** Replace the per-frame `positionChanged` gate in [`PlayerMovementController.cs:1261-1275`](../../../src/AcDream.App/Input/PlayerMovementController.cs:1261) with retail's narrow gate per `acclient_2013_pseudo_c.txt:700233-700285`:

```csharp
// During sub-interval: send only on cell-or-contact-plane change.
// After interval elapses: send only if position/frame changed.
// Retail-faithful per acclient_2013_pseudo_c.txt:700233 ShouldSendPositionEvent.
bool intervalElapsed = !_lastSentInitialized
    || (_simTimeSeconds - _lastSentTime) >= HeartbeatInterval;

bool cellChanged  = _lastSentCellId != CellId;
bool planeChanged = !_lastSentContactPlane.Equals(_body.ContactPlane);
bool frameChanged = !ApproxPositionEqual(_lastSentPos, _body.Position);

bool sendThisFrame = intervalElapsed
    ? (cellChanged || frameChanged)
    : (cellChanged || planeChanged);

HeartbeatDue = _body.InContact && _body.OnWalkable && sendThisFrame;
```

`_lastSentContactPlane` requires adding a `System.Numerics.Plane _lastSentContactPlane;` field next to the other `_lastSent*` fields. `System.Numerics.Plane` is a struct with `IEquatable<Plane>` so direct `!_lastSentContactPlane.Equals(_body.ContactPlane)` works. Extend `NotePositionSent` to accept a `Plane` and stamp it alongside position/cell/time. The outbound layer at `GameWindow.cs:6410-6445` (MoveToState) and `~line 6310` (AutonomousPosition) both gain a `contactPlane: _body.ContactPlane` argument.

### Issues closed

- **#63** — server-initiated auto-walk not honored. (Both halves: B.6 slice 2 shipped the inbound handling on 2026-05-14; this commit fixes the MoveToChain callback-cancellation gap.)
- **#74** — AP cadence chattier than retail. (Direct revert to retail's narrow gate enabled by the workaround retirement.)

## Out of scope (file as new issues)

- **Retail status messages** ("Approaching {target}" / "Using the {target}" on screen). Client-side UX polish; not wire-critical. Mentioned by user during brainstorm 2026-05-16 as nice-to-have to match retail feel. File as `#75 — Retail-faithful pending-action status messages on screen`.

## Testing plan

### Unit tests

No new unit tests required. The behavioral change is wire-level integration; existing Core.Net 294 baseline must hold. Existing 1073 Core tests baseline must hold (8 pre-existing physics failures unchanged).

### Visual verification (user-driven)

1. **Far-range Use NPC.** Double-click a Pathwarden / Royal Guard ~8-15 m away. Expected log shape:
   ```
   [B.4b] use guid=0x... seq=X
   [autowalk-mt] mt=0x06 isMoveTo=True ...
   [autowalk-begin] dest=...
   [autowalk-end] reason=arrived
   ```
   **Expected: NO `[B.4b] use-deferred` line.** Dialogue fires from ACE's callback. One Use packet on the wire, not two.

2. **Far-range PickUp item.** F-key a ground item ~5-10 m away. Same shape — one PickUp, no retry.

3. **Close-range Use NPC behind player.** Within 3 m of an NPC facing away, press R. Body turns 180°, then dialogue fires. The close-range deferred path is unchanged by this work; should still produce:
   ```
   [B.4b] use deferred (close-range, turn-first)
   [autowalk-end] reason=arrived
   [B.4b] use-deferred
   ```
   (`use-deferred` is correct here — close-range deferral is retail-faithful turn-first, not a workaround.)

4. **Open inn door from across the room.** Walks, opens. ONE `[B.4b] use` line, no retry, no double-open.

5. **User takes manual control mid-auto-walk.** Click far NPC → during the walk, press W. Auto-walk cancels via `user-input`, normal MoveToState resumes firing. The action does NOT fire on arrival (user cancelled).

6. **Rapid click between two targets.** Click NPC, before arrival click a second NPC. ACE re-broadcasts MoveToObject with the new target. Our overlay re-targets (existing `BeginServerAutoWalk` overwrite). Action fires on arrival at the SECOND target. No stale `_pendingPostArrivalAction` from the first click (close-range path keeps its handling; far-range no longer queues anything).

### Pre-conditions

- ACE running on `127.0.0.1:9000`.
- `+Acdream` character at Holtburg (test character).
- `ACDREAM_PROBE_AUTOWALK=1` for the trace lines.
- Build green: `dotnet build src/AcDream.App/AcDream.App.csproj -c Debug`.

## Acceptance criteria

- All six visual-verify scenarios pass.
- No `use-deferred` log line for FAR-range Use (only for close-range turn-first defer, which is correct).
- Core.Net tests pass (294/294).
- Core tests baseline holds (1073/1081).
- Issues #63 and #74 close with this commit's SHA.

## Risk + rollback

**Risk:** If ACE's `MoveToChain` somehow STILL doesn't fire the callback (e.g., a separate ACE bug we haven't identified), Use action breaks for far-range targets. The user would observe "walked to NPC, no dialogue."

**Rollback:** trivial git revert. The fix is one guard clause + workaround deletions. Reverting restores the working-but-chatty Commit B state at `b5da17d`.

**Detection during visual verify:** if scenario 1 fails (no dialogue after arrival), revert before merging.

## Plan handoff

This design is the input for `superpowers:writing-plans`, which produces the task-by-task plan with code blocks ready to paste.
