diff --git a/client/scripts/autoloads/sim_bridge.gd b/client/scripts/autoloads/sim_bridge.gd
index d3dca48f5..7095e919a 100644
--- a/client/scripts/autoloads/sim_bridge.gd
+++ b/client/scripts/autoloads/sim_bridge.gd
@@ -6,6 +6,8 @@ enum ConnectionState { DISCONNECTED, CONNECTING, CONNECTED, ERROR }
 var state: ConnectionState = ConnectionState.DISCONNECTED
 var test_mode: bool = true  # Enable test mode for development without Rust server
 var _test_tick: int = 0
+var _last_snapshot: Variant = null  # Most recent decoded snapshot (consumed by poll_snapshot)
+var _outbound_buffer: Array[PackedByteArray] = []  # Encoded inputs awaiting transport
 
 # Signals
 signal connection_state_changed(old_state: ConnectionState, new_state: ConnectionState)
@@ -35,14 +37,22 @@ func connect_to_sim() -> void:
 func disconnect_from_sim() -> void:
 	_set_state(ConnectionState.DISCONNECTED)
 
-# Send input to simulation (real implementation comes later)
+# Send input to simulation server.
+# player_input: Dictionary with "action" (int from InputMapper.Action enum) and "timestamp_msec".
+# In test mode, inputs are silently dropped. Transport (ticket #79) will send the bytes.
 func send_input(player_input: Dictionary) -> void:
 	if state != ConnectionState.CONNECTED:
 		return
-	# TODO: Serialize and send via MessagePack when IPC is implemented
-	pass
+	if test_mode:
+		return
+	var action_name := _action_enum_to_wire(player_input.get("action", -1))
+	if action_name.is_empty():
+		return
+	var tick: int = player_input.get("timestamp_msec", 0)
+	_outbound_buffer.append(Protocol.encode_player_input(tick, action_name))
 
-# Poll for snapshot from simulation
+# Poll for snapshot from simulation.
+# In test mode returns hardcoded data. In live mode, returns the last decoded snapshot (if any).
 func poll_snapshot() -> Variant:
 	if state != ConnectionState.CONNECTED:
 		return null
@@ -52,9 +62,40 @@ func poll_snapshot() -> Variant:
 		snapshot_received.emit(snapshot)
 		return snapshot
 
-	# TODO: Actual polling logic when IPC/MessagePack is implemented
+	if _last_snapshot != null:
+		var snapshot = _last_snapshot
+		_last_snapshot = null
+		snapshot_received.emit(snapshot)
+		return snapshot
+
 	return null
 
+# Called by transport layer (ticket #79) when raw bytes arrive from the server.
+func receive_bytes(bytes: PackedByteArray) -> void:
+	var snapshot = Protocol.decode_snapshot(bytes)
+	if snapshot != null:
+		_last_snapshot = snapshot
+
+# Drain the outbound buffer. Called by transport layer (ticket #79) to get encoded messages.
+func drain_outbound() -> Array[PackedByteArray]:
+	var messages = _outbound_buffer.duplicate()
+	_outbound_buffer.clear()
+	return messages
+
+# Map InputMapper.Action enum values to wire-format action names (matching Rust PlayerAction).
+static func _action_enum_to_wire(action: int) -> String:
+	match action:
+		0: return "MoveNorth"   # InputMapper.Action.MOVE_NORTH
+		1: return "MoveSouth"   # InputMapper.Action.MOVE_SOUTH
+		2: return "MoveEast"    # InputMapper.Action.MOVE_EAST
+		3: return "MoveWest"    # InputMapper.Action.MOVE_WEST
+		4: return "Interact"    # InputMapper.Action.INTERACT
+		5: return "UsePerceptionMode"  # InputMapper.Action.USE_PERCEPTION_MODE
+		7: return "Pause"       # InputMapper.Action.PAUSE
+		_:
+			push_warning("SimBridge: unknown action enum %s" % action)
+			return ""
+
 # Hardcoded test snapshot for development (deterministic per D-010 principle 4)
 func _test_snapshot() -> Dictionary:
 	_test_tick += 1