test(scenes): ✅ Add and update test logic in courier_era2_round_trip_proof.gd and courier_era2_round_trip_proof.tscn to verify round-trip behavior for courier era 2.

Co-Authored-By: Lilith Autocommit <noreply@atlilith.com>

src/game/engine/scenes/tests/courier_era2_round_trip_proof.gd

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+extends Node
+## p3-01 bullet 11: era_2 courier round-trip proof.
+## Signs a SharedMapAgreement between two players whose capitals are 4 hexes
+## apart, dispatches an era_2 (foot_runner, 1 hex/turn) courier via straight-
+## line movement, and steps turn-by-turn until SharedMapDelivered fires.
+## Asserts delivery occurs within 6 steps and the share-window opens.
+
+var _pass_count: int = 0
+var _fail_count: int = 0
+
+
+func _ready() -> void:
+	if not ClassDB.class_exists("GdTradeLedger"):
+		print("[SKIP] GdTradeLedger not registered — GDExtension not loaded")
+		get_tree().quit(0)
+		return
+	_run_proof()
+	_print_results()
+	get_tree().quit(0 if _fail_count == 0 else 1)
+
+
+func _run_proof() -> void:
+	# Build a GameState with two players whose capitals are 4 hexes apart.
+	var state: RefCounted = ClassDB.instantiate("GdGameState") as RefCounted
+	if not _assert("GdGameState instantiates", state != null):
+		return
+	state.call("create_grid", 10, 10)
+	state.call("add_player_militarist", 0, 0)   # player 0 capital at (0,0)
+	state.call("add_player_militarist", 4, 0)   # player 1 capital at (4,0)
+
+	# Build the courier map view from that state.
+	var map_view_inst: RefCounted = ClassDB.instantiate("GdCourierMapView") as RefCounted
+	if not _assert("GdCourierMapView instantiates", map_view_inst != null):
+		return
+	# from_game_state is a static constructor; call it via instance in GDScript.
+	var gd_map_view: RefCounted = map_view_inst.call("from_game_state", state) as RefCounted
+	if not _assert("GdCourierMapView.from_game_state returns non-null", gd_map_view != null):
+		return
+
+	var gd_trade: RefCounted = ClassDB.instantiate("GdTrade") as RefCounted
+	if not _assert("GdTrade instantiates", gd_trade != null):
+		return
+
+	# Build a SharedMapAgreement and an era_2 courier route, add to ledger.
+	var sm: RefCounted = gd_trade.call("shared_map_agreement_new", 0, 1, 50, 6) as RefCounted
+	if not _assert("SharedMapAgreement created", sm != null):
+		return
+
+	var route: RefCounted = gd_trade.call("courier_route_new", 0, 1) as RefCounted
+	if not _assert("CourierRoute created", route != null):
+		return
+
+	# Build ledger JSON with the era_2 courier at position (0,0), no path
+	# (straight-line fallback moves 1 hex/turn toward (4,0)).
+	var ledger_inst: RefCounted = ClassDB.instantiate("GdTradeLedger") as RefCounted
+	if not _assert("GdTradeLedger instantiates", ledger_inst != null):
+		return
+
+	var agreement_json: String = JSON.stringify({
+		"agreements": [
+			{
+				"SharedMap": {
+					"agreement_id": 0,
+					"partners": [0, 1],
+					"turn_started": 1,
+					"duration": 6,
+					"share_turns_remaining": 0,
+					"payment_gold": 50,
+					"payment_luxury": null,
+					"courier_route": {
+						"sender": 0,
+						"receiver": 1,
+						"courier_era_tier": 2,
+						"dispatched_turn": 1,
+						"position": [0, 0],
+						"eta_turn": null,
+						"delivered": false,
+						"intercepted": false,
+						"planned_path": [],
+						"path_step": 0
+					}
+				}
+			}
+		],
+		"next_agreement_id": 1
+	})
+	# from_json is a static factory; in GDScript call via instance.
+	var ledger: RefCounted = ledger_inst.call("from_json", agreement_json) as RefCounted
+	if not _assert("Ledger loads from JSON", ledger != null):
+		return
+
+	# Step up to 20 turns; era_2 moves 1 hex/turn, 4 hexes → deliver by turn 4.
+	var delivered_event_found: bool = false
+	var delivered_turn: int = -1
+	for turn: int in range(1, 21):
+		var events: Array = gd_trade.call("step_shared_map_agreements", ledger, gd_map_view, turn) as Array
+		for ev: Dictionary in events:
+			if ev.get("type") == "shared_map_delivered":
+				delivered_event_found = true
+				delivered_turn = turn
+				break
+		if delivered_event_found:
+			break
+
+	_assert("SharedMapDelivered event emitted within 20 steps", delivered_event_found)
+	_assert("Delivery happens by turn 6 (4 hexes at 1/turn + slack)", delivered_turn <= 6)
+
+	# After delivery the agreement should be in the share-window phase.
+	var sm_agreements: Array = ledger.call("iter_shared_map") as Array
+	_assert("Ledger contains SharedMap agreement after delivery", sm_agreements.size() == 1)
+	if sm_agreements.size() > 0:
+		var sm_out: RefCounted = sm_agreements[0] as RefCounted
+		_assert("Agreement is_delivered", sm_out.call("is_delivered") as bool)
+		var share_remaining: int = sm_out.call("get_share_turns_remaining") as int
+		_assert("Share window is open (turns_remaining > 0)", share_remaining > 0)
+
+
+func _assert(label: String, condition: bool) -> bool:
+	if condition:
+		_pass_count += 1
+		print("[PASS] %s" % label)
+	else:
+		_fail_count += 1
+		push_error("[FAIL] %s" % label)
+	return condition
+
+
+func _print_results() -> void:
+	print("courier_era2_round_trip_proof: %d passed, %d failed" % [_pass_count, _fail_count])

src/game/engine/scenes/tests/courier_era2_round_trip_proof.tscn

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+[gd_scene load_steps=2 format=3 uid="uid://courier_era2_round_trip"]
+
+[ext_resource type="Script" path="res://engine/scenes/tests/courier_era2_round_trip_proof.gd" id="1"]
+
+[node name="CourierEra2RoundTripProof" type="Node"]
+script = ExtResource("1")