fix(ui): agent driver honors SR_PORT — the eyeball's own finding (T-971)

The channel eyeball caught the committed reference driver silently
relying on SimBridge's hardcoded default port, unlike every sibling
real-render driver — a caller starting the server on a chosen port got
20 silent connect retries against the wrong port and a hollow session
whose results had valid shapes but no data. Mirrors visual_capture.gd's
convention exactly: SR_LIVE=1 without SR_PORT is a hard error; SR_PORT
sets SimBridge.server_port before boot.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

client/tests/atlas_agent_driver.gd

@@ -99,6 +99,25 @@ func _run() -> void:
 		quit(1)
 		return
 
+	# SR_PORT wiring (PR #209 eyeball finding) — mirror visual_capture.gd's
+	# live-mode convention exactly: every sibling real-render driver
+	# (visual_capture, atlas_standalone, locomotion_sandbox) reads SR_PORT
+	# rather than silently relying on SimBridge's hardcoded default port;
+	# without this, a caller who started the server on a chosen port (the
+	# run-visual --port pattern) gets 20 silent connect retries against the
+	# wrong port and a hollow session whose act() results still have valid
+	# SHAPES but no data behind them. SR_LIVE=1 without SR_PORT is a hard
+	# error, same as visual_capture.gd.
+	if OS.get_environment("SR_LIVE") == "1":
+		var port_env := OS.get_environment("SR_PORT")
+		if port_env.is_empty():
+			push_error("atlas_agent_driver: SR_LIVE=1 but SR_PORT not set")
+			quit(1)
+			return
+		var sim_bridge := root.get_node("/root/SimBridge")
+		sim_bridge.server_port = int(port_env)
+		print("atlas_agent_driver: live mode — server port %d" % sim_bridge.server_port)
+
 	var main_scene = load("res://scenes/main.tscn")
 	var main_node = main_scene.instantiate()