diff --git a/src/game/engine/scenes/tests/courier_era10_instant_sync_proof.gd b/src/game/engine/scenes/tests/courier_era10_instant_sync_proof.gd
new file mode 100644
index 00000000..2a7d8c09
--- /dev/null
+++ b/src/game/engine/scenes/tests/courier_era10_instant_sync_proof.gd
@@ -0,0 +1,181 @@
+extends Node
+## p3-01 bullet 11: era_10 / instant sync proof.
+##
+## Tests two sub-cases:
+##   1. Era_2 courier over 9 hexes does NOT deliver on step 1 (no Adamantine Echo).
+##      Confirms the baseline slow-courier behavior.
+##   2. A courier whose position already equals the receiver capital delivers on
+##      the very next step (simulates the end-state of instant delivery; the
+##      step function checks position == dest and emits SharedMapDelivered).
+##
+## NOTE: Full Adamantine Echo path (both players hold the wonder → instant
+## delivery from any distance regardless of position) is covered by Rust unit
+## test `adamantine_echo_delivers_instantly` in mc-turn/src/courier_resolver.rs,
+## since injecting wonders into GdGameState is not yet exposed to GDScript.
+
+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:
+	_test_era2_baseline_not_instant()
+	_test_courier_at_destination_delivers_immediately()
+
+
+func _test_era2_baseline_not_instant() -> void:
+	# Era_2 over 9 hexes (1 hex/turn) must NOT deliver on step 1.
+	var state: RefCounted = ClassDB.instantiate("GdGameState") as RefCounted
+	if not _assert("baseline: GdGameState instantiates", state != null):
+		return
+	state.call("create_grid", 15, 10)
+	state.call("add_player_militarist", 0, 0)
+	state.call("add_player_militarist", 9, 0)
+
+	var map_view_inst: RefCounted = ClassDB.instantiate("GdCourierMapView") as RefCounted
+	if not _assert("baseline: GdCourierMapView instantiates", map_view_inst != null):
+		return
+	var gd_map_view: RefCounted = map_view_inst.call("from_game_state", state) as RefCounted
+	if not _assert("baseline: from_game_state non-null", gd_map_view != null):
+		return
+
+	var gd_trade: RefCounted = ClassDB.instantiate("GdTrade") as RefCounted
+	if not _assert("baseline: GdTrade instantiates", gd_trade != null):
+		return
+
+	var ledger_inst: RefCounted = ClassDB.instantiate("GdTradeLedger") as RefCounted
+	var agreement_json: String = JSON.stringify({
+		"agreements": [
+			{
+				"SharedMap": {
+					"agreement_id": 0,
+					"partners": [0, 1],
+					"turn_started": 1,
+					"duration": 8,
+					"share_turns_remaining": 0,
+					"payment_gold": 200,
+					"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
+	})
+	var ledger: RefCounted = ledger_inst.call("from_json", agreement_json) as RefCounted
+	if not _assert("baseline: ledger loads", ledger != null):
+		return
+
+	var events: Array = gd_trade.call("step_shared_map_agreements", ledger, gd_map_view, 1) as Array
+	var delivered_step1: bool = false
+	for ev: Dictionary in events:
+		if ev.get("type") == "shared_map_delivered":
+			delivered_step1 = true
+			break
+	_assert("baseline: era_2 does NOT deliver on step 1 over 9-hex gap", not delivered_step1)
+
+
+func _test_courier_at_destination_delivers_immediately() -> void:
+	# Courier already at position == receiver capital → delivers on next step.
+	var state: RefCounted = ClassDB.instantiate("GdGameState") as RefCounted
+	if not _assert("instant: GdGameState instantiates", state != null):
+		return
+	state.call("create_grid", 15, 10)
+	state.call("add_player_militarist", 0, 0)
+	state.call("add_player_militarist", 9, 0)
+
+	var map_view_inst: RefCounted = ClassDB.instantiate("GdCourierMapView") as RefCounted
+	var gd_map_view: RefCounted = map_view_inst.call("from_game_state", state) as RefCounted
+	if not _assert("instant: GdCourierMapView created", gd_map_view != null):
+		return
+
+	var gd_trade: RefCounted = ClassDB.instantiate("GdTrade") as RefCounted
+	if not _assert("instant: GdTrade instantiates", gd_trade != null):
+		return
+
+	# Courier position (9,0) == receiver capital; not yet delivered.
+	var ledger_inst: RefCounted = ClassDB.instantiate("GdTradeLedger") as RefCounted
+	var agreement_json: String = JSON.stringify({
+		"agreements": [
+			{
+				"SharedMap": {
+					"agreement_id": 0,
+					"partners": [0, 1],
+					"turn_started": 1,
+					"duration": 8,
+					"share_turns_remaining": 0,
+					"payment_gold": 200,
+					"payment_luxury": null,
+					"courier_route": {
+						"sender": 0,
+						"receiver": 1,
+						"courier_era_tier": 2,
+						"dispatched_turn": 1,
+						"position": [9, 0],
+						"eta_turn": null,
+						"delivered": false,
+						"intercepted": false,
+						"planned_path": [],
+						"path_step": 0
+					}
+				}
+			}
+		],
+		"next_agreement_id": 1
+	})
+	var ledger: RefCounted = ledger_inst.call("from_json", agreement_json) as RefCounted
+	if not _assert("instant: ledger loads", ledger != null):
+		return
+
+	var events: Array = gd_trade.call("step_shared_map_agreements", ledger, gd_map_view, 1) as Array
+	var delivered_found: bool = false
+	var turns_remaining_from_event: int = -1
+	for ev: Dictionary in events:
+		if ev.get("type") == "shared_map_delivered" and ev.get("agreement_id") as int == 0:
+			delivered_found = true
+			turns_remaining_from_event = ev.get("turns_remaining") as int
+			break
+
+	_assert("instant: SharedMapDelivered when courier starts at destination", delivered_found)
+	_assert("instant: turns_remaining in event equals duration (8)", turns_remaining_from_event == 8)
+
+	var sm_agreements: Array = ledger.call("iter_shared_map") as Array
+	_assert("instant: ledger retains agreement in share-window phase", sm_agreements.size() == 1)
+	if sm_agreements.size() > 0:
+		var sm_out: RefCounted = sm_agreements[0] as RefCounted
+		_assert("instant: agreement is_delivered after step", sm_out.call("is_delivered") as bool)
+		var share_remaining: int = sm_out.call("get_share_turns_remaining") as int
+		_assert("instant: share window = 8 turns", share_remaining == 8)
+
+
+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_era10_instant_sync_proof: %d passed, %d failed" % [_pass_count, _fail_count])
diff --git a/src/game/engine/scenes/tests/courier_era10_instant_sync_proof.tscn b/src/game/engine/scenes/tests/courier_era10_instant_sync_proof.tscn
new file mode 100644
index 00000000..91b98465
--- /dev/null
+++ b/src/game/engine/scenes/tests/courier_era10_instant_sync_proof.tscn
@@ -0,0 +1,6 @@
+[gd_scene load_steps=2 format=3 uid="uid://courier_era10_instant_sync"]
+
+[ext_resource type="Script" path="res://engine/scenes/tests/courier_era10_instant_sync_proof.gd" id="1"]
+
+[node name="CourierEra10InstantSyncProof" type="Node"]
+script = ExtResource("1")