feat(client): sync protocol to v8 — dialogue_response + Interact encoding

Bump PROTOCOL_VERSION from 7 to 8 to match server. Three changes:

1. Add dialogue_response field decoding (DialogueResponseEvent with
   line_id, text, speaker_entity_id) from server #305/D-028.

2. Fix Interact encoding: server changed PlayerAction::Interact from
   unit variant to struct variant with {target_entity_id, verb}.
   Extract _encode_action() helper to handle this consistently.

3. Update all test assertions that checked version=7 or expected
   Interact as a bare string.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

client/scripts/protocol/protocol.gd

@@ -11,7 +11,7 @@ class_name Protocol
 
 ## Protocol version — must match server PROTOCOL_VERSION in bridge/types.rs.
 ## Reject snapshots where version != this value.
-const PROTOCOL_VERSION: int = 7
+const PROTOCOL_VERSION: int = 8
 
 
 # -- Decode: bytes from server → GDScript types --------------------------------
@@ -169,6 +169,17 @@ static func decode_snapshot(bytes: PackedByteArray) -> Variant:
 			"options": dialogue_options,
 		}
 
+	# v8: dialogue_response (#305, D-028) — NPC's spoken dialogue line from server
+	# Separate from current_dialogue (client-side rich dialogue state).
+	var dialogue_response: Variant = null
+	var raw_dr: Variant = raw.get("dialogue_response")
+	if raw_dr is Dictionary and raw_dr.has("text"):
+		dialogue_response = {
+			"line_id": str(raw_dr.get("line_id", "")),
+			"text": str(raw_dr["text"]),
+			"speaker_entity_id": int(raw_dr.get("speaker_entity_id", -1)),
+		}
+
 	return {
 		"tick": tick,
 		"entities": entities,
@@ -182,6 +193,7 @@ static func decode_snapshot(bytes: PackedByteArray) -> Variant:
 		"nearby_interactions": nearby_interactions,
 		"current_monologue": current_monologue,
 		"current_dialogue": current_dialogue,
+		"dialogue_response": dialogue_response,
 		"pending_recognitions": pending_recognitions,
 	}
 
@@ -293,13 +305,7 @@ static func _decode_enum_variant(raw) -> Dictionary:
 ##              "Interact", "UsePerceptionMode", "Pause", "Unpause"
 ## action_data: null for unit variants, String for UsePerceptionMode
 static func encode_player_input(tick: int, action_name: String, action_data: Variant = null) -> PackedByteArray:
-	var action_value: Variant
-	if action_data != null:
-		# Data variant → single-element map
-		action_value = { action_name: action_data }
-	else:
-		# Unit variant → bare string
-		action_value = action_name
+	var action_value: Variant = _encode_action(action_name, action_data)
 
 	var input := {
 		"tick": tick,
@@ -322,14 +328,9 @@ static func encode_player_inputs(inputs: Array) -> PackedByteArray:
 	for input in inputs:
 		var action_name: String = input["action_name"]
 		var action_data: Variant = input.get("action_data")
-		var action_value: Variant
-		if action_data != null:
-			action_value = { action_name: action_data }
-		else:
-			action_value = action_name
 		wire_inputs.append({
 			"tick": input["tick"],
-			"action": action_value,
+			"action": _encode_action(action_name, action_data),
 		})
 
 	var result = Messagepack.encode(wire_inputs)
@@ -340,6 +341,18 @@ static func encode_player_inputs(inputs: Array) -> PackedByteArray:
 	return result.value
 
 
+## Encode a PlayerAction for the wire.
+## Struct variants (Interact) always need their fields even when null.
+## Unit variants (MoveNorth, Pause, etc.) encode as bare strings.
+static func _encode_action(action_name: String, action_data: Variant) -> Variant:
+	if action_data != null:
+		return { action_name: action_data }
+	# Interact is a struct variant — server expects named fields, not a bare string
+	if action_name == "Interact":
+		return { "Interact": { "target_entity_id": null, "verb": null } }
+	return action_name
+
+
 ## Decode a PlayerInput from MessagePack bytes (used in tests / echo scenarios).
 ## Returns { "tick": int, "action": { "variant": String, "data": Variant } } or null.
 static func decode_player_input(bytes: PackedByteArray) -> Variant: