NEO-22: fix stream rubber-banding (coalesce, idle gate, soft snap)

Queue only latest move-stream target per POST; clear pending while busy.
Skip stream submits when idle; skip tiny authoritative snaps after boot.

client/README.md

@@ -53,7 +53,7 @@ Elevated walkables use **distinct albedo tints** in `scenes/main.tscn` so screen
 
 ## Authoritative movement (NEO-7, NEO-11, NEO-22)
 
-With the game server running ([`server/README.md`](../server/README.md)), **WASD** (input actions **`move_*`** in `project.godot`) drives **camera-relative XZ** wish direction on the **`Player`**, and **`main.gd`** periodically **`POST`**s **`/game/players/{id}/move-stream`** with a batch of **absolute** world positions (NEO-22 **option C**). The server validates each leg with the same rules as a single **`MoveCommand`**, applies **all targets in order** (reject = **no** partial apply), and returns **`PositionStateResponse`**; the client **snaps** to that position. **`POST /game/players/{id}/move`** remains for **debug** click-to-move when running a **debug** Godot build (`ground_pick.gd` only listens in **`OS.is_debug_build()`**): it still does **POST** + **`GET`** verify and sets a **nav walk goal** on the player.
+With the game server running ([`server/README.md`](../server/README.md)), **WASD** (input actions **`move_*`** in `project.godot`) drives **camera-relative XZ** wish direction on the **`Player`**, and **`main.gd`** periodically **`POST`**s **`/game/players/{id}/move-stream`** with the **latest** body-centre sample while you are moving (no stream while standing still, so idle anchor does not fight HTTP). **`PositionAuthorityClient`** coalesces to **one target per request** so a slow round-trip cannot apply a stale multi-step chain after the capsule has moved. The server validates each leg with the same rules as a single **`MoveCommand`**, applies **all targets in order** (reject = **no** partial apply), and returns **`PositionStateResponse`**; the client **snaps** when the correction exceeds a small threshold (boot snap always applies once). **`POST /game/players/{id}/move`** remains for **debug** click-to-move when running a **debug** Godot build (`ground_pick.gd` only listens in **`OS.is_debug_build()`**): it still does **POST** + **`GET`** verify and sets a **nav walk goal** on the player.
 
 **Boot** `sync_from_server()` **snaps** once so spawn matches the server.
 

client/scripts/main.gd

@@ -23,9 +23,18 @@ const MOVE_REJECT_MSG_SECONDS: float = 4.0
 ## Throttle `move-stream` POSTs (~20 Hz at 120 physics ticks/sec).
 const STREAM_PHYSICS_INTERVAL: int = 6
 
+## Skip `move-stream` while standing still so idle + anchor are not fighting HTTP snaps.
+const STREAM_IDLE_VEL_HZ_SQ: float = 0.0004
+
+## Ignore authority snaps smaller than this (m) to avoid micro-flicker from float / echo noise.
+const AUTH_SNAP_MIN_HORIZONTAL: float = 0.08
+const AUTH_SNAP_MIN_VERTICAL: float = 0.04
+
 ## Bump on each rejection so older one-shot timers do not clear a newer message.
 var _move_reject_msg_token: int = 0
 var _stream_physics_counter: int = 0
+## After the first `apply_as_snap` authority update, micro-snaps may be skipped (boot always applies).
+var _allow_authority_soft_snap_skip: bool = false
 
 ## [InputMap] [code]dev_toggle_occluder_obstacle[/code] (default **Ctrl+Shift+K**):
 ## Restored when the obstacle is shown again.
@@ -75,11 +84,16 @@ func _physics_process(_delta: float) -> void:
 		return
 	var wish: Vector3 = _locomotion_wish_world_xz_from_camera()
 	_player.call("set_locomotion_wish_world_xz", wish)
-	_stream_physics_counter += 1
-	if _stream_physics_counter >= STREAM_PHYSICS_INTERVAL:
+	var vel_hz_sq: float = Vector2(_player.velocity.x, _player.velocity.z).length_squared()
+	var moving: bool = wish.length_squared() > 1e-10 or vel_hz_sq > STREAM_IDLE_VEL_HZ_SQ
+	if moving:
+		_stream_physics_counter += 1
+		if _stream_physics_counter >= STREAM_PHYSICS_INTERVAL:
+			_stream_physics_counter = 0
+			var batch: Array = [_player.global_position]
+			_authority.call("submit_stream_targets", batch)
+	else:
 		_stream_physics_counter = 0
-		var batch: Array = [_player.global_position]
-		_authority.call("submit_stream_targets", batch)
 	var p: Vector3 = _player.global_position
 	_player_pos_label.text = "x: %.3f\ny: %.3f\nz: %.3f" % [p.x, p.y, p.z]
 
@@ -111,6 +125,13 @@ func _on_target_chosen(world: Vector3) -> void:
 
 func _on_authoritative_position(world: Vector3, apply_as_snap: bool) -> void:
 	if apply_as_snap:
+		if _allow_authority_soft_snap_skip:
+			var p: Vector3 = _player.global_position
+			var dh: float = Vector2(world.x - p.x, world.z - p.z).length()
+			var dy: float = absf(world.y - p.y)
+			if dh < AUTH_SNAP_MIN_HORIZONTAL and dy < AUTH_SNAP_MIN_VERTICAL:
+				return
+		_allow_authority_soft_snap_skip = true
 		_player.snap_to_server(world)
 	else:
 		_player.set_authoritative_nav_goal(world)

client/scripts/position_authority_client.gd

@@ -58,8 +58,13 @@ func submit_move_target(world: Vector3) -> void:
 	_start_move_post(world)
 
 
-## NEO-22: append samples; sends up to [constant MOVE_STREAM_MAX_PER_REQUEST] per POST when idle.
+## NEO-22: append samples; each POST sends **only the latest** queued position so slow HTTP cannot
+## apply a stale multi-step chain after the capsule has already moved (rubber-band / bounce).
 func submit_stream_targets(targets: Array) -> void:
+	if _busy:
+		# In-flight POST already encodes an older chain; drop queued crumbs so we do not replay
+		# past intent after this response lands.
+		_stream_queue.clear()
 	for t: Variant in targets:
 		if t is Vector3:
 			_stream_queue.append(t as Vector3)
@@ -72,11 +77,9 @@ func _try_flush_pending() -> void:
 	if _busy:
 		return
 	if not _stream_queue.is_empty():
-		var n: int = mini(_stream_queue.size(), MOVE_STREAM_MAX_PER_REQUEST)
-		var batch: Array = []
-		for i in range(n):
-			batch.append(_stream_queue[i])
-		_start_stream_post(batch)
+		var latest: Vector3 = _stream_queue[_stream_queue.size() - 1]
+		_stream_queue.clear()
+		_start_stream_post([latest])
 		return
 	if _pending_move_target is Vector3:
 		var w: Vector3 = _pending_move_target as Vector3
@@ -200,10 +203,7 @@ func _on_request_completed(
 				_busy = false
 				_try_flush_pending()
 				return
-			# Drop the batch we sent (validated + applied as a unit on the server).
-			var drop: int = mini(_stream_in_flight_count, _stream_queue.size())
-			if drop > 0:
-				_stream_queue = _stream_queue.slice(drop)
+			# Queue was cleared when the POST started; nothing to drop.
 			_stream_in_flight_count = 0
 			_busy = false
 			if response_code == 200: