readability: extract magic constants, fix Go jargon

- goos/goarch -> os_name/arch_name (Go ecosystem jargon)
- BUTLER_USER_AGENT now reads version from plugin.json at runtime
- Added named constants: CONNECTION_TIMEOUT_ITERATIONS,
  CONNECTION_POLL_DELAY_MS, PERCENTAGE_SCALE, LAUNCH_WATCH_INTERVAL_SEC,
  UPDATE_CHECK_INTERVAL_SEC, BUTLERD_BOOT_MAX_ATTEMPTS,
  BUTLERD_BOOT_RETRY_DELAY_SEC, LAUNCH_WATCH_TIMEOUT_MS,
  EXECUTE_PERMISSION_BIT
- Removed BYTES_PER_MB (inline 1024 * 1024 is clearer)

core/itch_client.gd

@@ -29,6 +29,9 @@ const butler_dir := "user://butler"
 ## survive plugin updates untouched.
 const games_dir := "user://butler/games"
 const CACHE_DIR := "itch"
+const CONNECTION_TIMEOUT_ITERATIONS := 50
+const CONNECTION_POLL_DELAY_MS := 20
+const PERCENTAGE_SCALE := 100
 
 enum STATE {
 	BOOT,
@@ -101,7 +104,7 @@ func bootstrap() -> void:
 		"--keep-alive",
 		"--dbpath", dbpath,
 		"--address", "https://itch.io",
-		"--user-agent", "OpenGamepadUI-itch/0.1.0",
+		"--user-agent", _get_user_agent(),
 		"--destiny-pid", str(OS.get_process_id()),
 	]
 
@@ -138,21 +141,21 @@ func _migrate_butler(dest_dir: String) -> void:
 ## Downloads a butler binary for this platform from itch's broth distribution
 ## channel (the same one the official itch.io app uses to self-update).
 func _install_butler() -> bool:
-	var goos := "linux"
+	var os_name := "linux"
-	var goarch := "amd64"
+	var arch_name := "amd64"
 	if OS.get_name() == "Windows":
-		goos = "windows"
+		os_name = "windows"
 	if OS.get_name() == "macOS":
-		goos = "darwin"
+		os_name = "darwin"
 	# Engine.get_architecture_name() is only available on newer Godot 4.x
 	# builds; guard it so this still works if OpenGamepadUI is running on an
 	# older engine version.
 	if Engine.has_method("get_architecture_name"):
 		var arch: String = Engine.get_architecture_name()
 		if "arm64" in arch or "aarch64" in arch:
-			goarch = "arm64"
+			arch_name = "arm64"
 
-	var platform_slug := goos + "-" + goarch
+	var platform_slug := os_name + "-" + arch_name
 	var latest_url := "/".join([broth_base, platform_slug, "LATEST"])
 
 	var http := HTTPRequest.new()
@@ -204,6 +207,17 @@ func _install_butler() -> bool:
 	return true
 
 
+func _get_user_agent() -> String:
+	var version := "unknown"
+	var file := FileAccess.open("res://plugin.json", FileAccess.READ)
+	if file:
+		var json: Variant = JSON.parse_string(file.get_as_text())
+		file.close()
+		if json is Dictionary:
+			version = json.get("plugin.version", "unknown")
+	return "OpenGamepadUI-itch/" + version
+
+
 # ---------------------------------------------------------------------------
 # Wire protocol: spawn -> read handshake off stdout -> connect TCP -> auth
 # ---------------------------------------------------------------------------
@@ -266,10 +280,10 @@ func _connect_and_authenticate(address: String, secret: String) -> void:
 		return
 
 	# Wait for the connection to establish
-	var timeout := 50
+	var timeout := CONNECTION_TIMEOUT_ITERATIONS
 	while socket.get_status() == StreamPeerTCP.STATUS_CONNECTING and timeout > 0:
 		socket.poll()
-		OS.delay_msec(20)
+		OS.delay_msec(CONNECTION_POLL_DELAY_MS)
 		timeout -= 1
 	if socket.get_status() != StreamPeerTCP.STATUS_CONNECTED:
 		logger.error("Timed out connecting to butlerd")
@@ -790,8 +804,8 @@ func _install(game: Dictionary, cave_id: String, options: Dictionary) -> bool:
 		var progress: float = p.get("progress", 0.0)
 		install_progressed.emit.call_deferred(
 			cave_id if cave_id != "" else str(game_id),
-			int(progress * 100),
+			int(progress * PERCENTAGE_SCALE),
-			100
+			PERCENTAGE_SCALE
 		)
 	rpc_notification.connect(on_notification)
 

core/library_itch.gd

@@ -2,6 +2,13 @@ extends Library
 
 const ItchClient := preload("res://plugins/itch/core/itch_client.gd")
 const _apps_cache_file: String = "apps.json"
+const LAUNCH_WATCH_INTERVAL_SEC := 2.0
+const UPDATE_CHECK_INTERVAL_SEC := 600.0
+const BUTLERD_BOOT_MAX_ATTEMPTS := 10
+const BUTLERD_BOOT_RETRY_DELAY_SEC := 0.5
+const LAUNCH_WATCH_TIMEOUT_MS := 5000
+## 0o111 — execute bit set for any of owner/group/others.
+const EXECUTE_PERMISSION_BIT := 73
 
 var settings_manager := load("res://core/global/settings_manager.tres") as SettingsManager
 
@@ -35,14 +42,14 @@ func _ready() -> void:
 	# instead of leaving the user stuck on a black in-game screen.
 	if load("res://core/global/launch_manager.tres") != null:
 		var watch_timer := Timer.new()
-		watch_timer.wait_time = 2.0
+		watch_timer.wait_time = LAUNCH_WATCH_INTERVAL_SEC
 		watch_timer.autostart = true
 		watch_timer.timeout.connect(_check_failed_launches)
 		add_child(watch_timer)
 	# Keep the has_update() flags fresh in the background (CheckUpdate hits the
 	# itch.io API, so it must never run on the UI thread or per-library-load).
 	var update_timer := Timer.new()
-	update_timer.wait_time = 600.0
+	update_timer.wait_time = UPDATE_CHECK_INTERVAL_SEC
 	update_timer.autostart = true
 	update_timer.timeout.connect(_refresh_update_flags)
 	add_child(update_timer)
@@ -502,8 +509,8 @@ func _load_library(caching_flags: int = Cache.FLAGS.LOAD | Cache.FLAGS.SAVE) ->
 					cached_installed = true
 					break
 			var attempts := 0
-			while cached_installed and attempts < 10 and (caves == null or (caves.is_empty() and itch.state != ItchClient.STATE.CONNECTED)):
+			while cached_installed and attempts < BUTLERD_BOOT_MAX_ATTEMPTS and (caves == null or (caves.is_empty() and itch.state != ItchClient.STATE.CONNECTED)):
-				await get_tree().create_timer(0.5).timeout
+				await get_tree().create_timer(BUTLERD_BOOT_RETRY_DELAY_SEC).timeout
 				caves = await itch.get_caves()
 				attempts += 1
 			var caves_by_game_id := {}
@@ -792,8 +799,7 @@ func _candidate_is_game_binary(path: String) -> bool:
 func _is_runnable_file(path: String) -> bool:
 	if path == "" or not FileAccess.file_exists(path):
 		return false
-	# 0o111 = execute bit set for any of owner/group/others.
+	return FileAccess.get_unix_permissions(path) & EXECUTE_PERMISSION_BIT != 0
-	return FileAccess.get_unix_permissions(path) & 73 != 0
 
 
 ## Looks up a runtime binary (love, java, ...). Checks the persistent runtime
@@ -839,7 +845,7 @@ func _check_failed_launches() -> void:
 			continue
 		if app.is_running():
 			continue
-		if now - int(_launch_watch[app.pid]) < 5000:
+		if now - int(_launch_watch[app.pid]) < LAUNCH_WATCH_TIMEOUT_MS:
 			continue
 		if app.pid in _diagnosed_pids:
 			continue