WIP checkpoint: Client-side position sync + prediction/reconciliation

scripts/network_client.gd

@@ -200,36 +200,35 @@ func _handle_snapshot(snapshot_data: Dictionary) -> void:
 		return
 
 	var authoritative_pos: Vector3 = (my_state as Dictionary).get("position", position)
-	var acked_seq: int = snapshot_data.get("tick", 0)
 
-	# Find our own predicted position at (approximately) the acknowledged
-	# tick -- the buffer is seq-ordered, so the first entry >= acked_seq is
-	# the comparison point. If the server hasn't caught up to any of our
-	# sent input yet (empty/very early buffer), nothing to reconcile.
-	var predicted_entry: Dictionary = {}
-	for entry in _prediction_buffer:
-		if entry["seq"] >= acked_seq:
-			predicted_entry = entry
-			break
-	if predicted_entry.is_empty():
+	# Real limitation, noted explicitly rather than silently faked: the
+	# server's snapshot_state (scripts/server.gd's _broadcast_snapshot) does
+	# not currently echo back "last input seq processed for this peer" --
+	# its `tick` field is the server's own internal simulation tick counter,
+	# a completely different clock from this client's per-input `_seq`. True
+	# tick-correlated rollback (docs/architecture/networking.md §5.2 step 4,
+	# "re-simulate any inputs that occurred after the server's tick") needs
+	# that ack echoed back per-peer -- a real, scoped follow-up, not
+	# something to fake here. Until then, reconcile against the MOST RECENT
+	# prediction (not a tick-matched one): still a real error measurement
+	# and a real correction, just without precise replay-from-exact-tick.
+	if _prediction_buffer.is_empty():
 		return
+	var latest_entry: Dictionary = _prediction_buffer[-1]
 
-	var error: float = (predicted_entry["position"] as Vector3).distance_to(authoritative_pos)
+	var error: float = (latest_entry["position"] as Vector3).distance_to(authoritative_pos)
 	if error <= RECONCILE_ERROR_THRESHOLD:
 		return  # Close enough -- prediction was correct, nothing to do.
 
-	# Correct: snap to the authoritative position, then replay every input
-	# sent after the acknowledged tick so the visible result still reflects
-	# input the server hasn't processed yet (§5.2 step 4).
+	# Correct: snap to the authoritative position. Without a real ack-seq
+	# from the server there's no reliable "replay inputs after this point"
+	# window to recompute, so the buffer is cleared and prediction resumes
+	# fresh from the corrected position on the next input -- still visibly
+	# responsive (no waiting for a round trip before the *next* input
+	# applies), just without this pass replaying in-flight inputs.
 	position = authoritative_pos
 	velocity = Vector3.ZERO
-	var replay_from_index := _prediction_buffer.find(predicted_entry) + 1
-	for i in range(replay_from_index, _prediction_buffer.size()):
-		var entry: Dictionary = _prediction_buffer[i]
-		var inp: Dictionary = entry["input"]
-		_apply_movement(1.0 / 30.0, inp.get("move_x", 0.0), inp.get("move_z", 0.0), inp.get("jump", false))
-		entry["position"] = position
-		entry["velocity"] = velocity
+	_prediction_buffer.clear()
 
 	reconciled.emit(error)