refactor(config): publish config singletons through atomic pointers

The three configuration singletons (C_globalConfig, C_botUserConfig,
C_botNodeConfig) were plain variables: LoadGlobalConfig and friends assigned
them from the goroutine handling a settings update, while bot pipes, the node
tracker and the HTTP handlers read them from their own goroutines. That is an
unsynchronized read of a concurrently written variable — a data race the race
detector reports, and one that already existed before any hot-reload work
because /api/webhook/add reloads the configuration while the bots run.

Replace them with atomic.Pointer values behind Current(), BotUsers() and
BotNodes(). Each reload builds a fresh value and publishes it atomically, so a
reader either sees the previous configuration or the new one, never a partial
one. Callers read through the accessor on every use instead of caching it.

Two spots that read several fields of one guard now snapshot once per call, so
a reload cannot split a combined check mid-flight:
- qq_napcat.handleNapcatEvent, which evaluates the debug guards per event
- the komari task-echo guard, now behind taskEchoEnabled()

The NapCat HTTP methods keep logging on showNapcatAction alone (without
requiring debugMode), matching their existing behaviour; that inconsistency
with the WebSocket path is preserved, not introduced, and is called out in
actionLogEnabled.

Also adds TestConcurrentReloadAndRead, which drives every accessor from four
reader goroutines while two writers reload the configuration, and sanitises the
member IDs used as test fixtures in config/settings_test.go.

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

config/variables.go

@@ -1,6 +1,9 @@
 package config
 
-import "sort"
+import (
+	"sort"
+	"sync/atomic"
+)
 
 // SystemConfig holds system-level configuration.
 type SystemConfig struct {
@@ -136,10 +139,11 @@ type WebhookReceiverConfig struct {
 // GetWebhookEndpoint returns the incoming webhook endpoint registered under the
 // given name, and whether such an endpoint exists.
 func GetWebhookEndpoint(name string) (WebhookEndpointConfig, bool) {
-	if C_globalConfig == nil {
+	cfg := Current()
+	if cfg == nil {
 		return WebhookEndpointConfig{}, false
 	}
-	endpoint, ok := C_globalConfig.Webhook.Endpoints[name]
+	endpoint, ok := cfg.Webhook.Endpoints[name]
 	return endpoint, ok
 }
 
@@ -165,7 +169,19 @@ type Config struct {
 	DBPath            string                  `json:"dbPath"`
 }
 
-var C_globalConfig *Config
+// globalConfig holds the configuration currently in effect. It is replaced as a
+// whole by LoadGlobalConfig — and therefore by every settings update — and never
+// mutated in place, so a reader that loads the pointer always observes a fully
+// initialized Config. Read it through Current rather than caching the result: a
+// cached pointer stops tracking reloads.
+var globalConfig atomic.Pointer[Config]
+
+// Current returns the configuration currently in effect, or nil before the
+// first successful LoadGlobalConfig. It is safe to call from any goroutine, and
+// must be called on every use rather than stored, so the caller sees reloads.
+func Current() *Config {
+	return globalConfig.Load()
+}
 
 // BotUserOptions holds per-member options stored in bot_user_config.json.
 type BotUserOptions struct {
@@ -220,7 +236,16 @@ type BotUserConfig struct {
 	Telegram BotUser_TelegramConfig `json:"telegram"`
 }
 
-var C_botUserConfig *BotUserConfig
+// botUserConfig mirrors bot_user_config.json the same way globalConfig mirrors
+// config.json: replaced wholesale on reload and read through BotUsers.
+var botUserConfig atomic.Pointer[BotUserConfig]
+
+// BotUsers returns the bot user configuration currently in effect, or nil
+// before the first successful LoadBotUserConfig. Like Current it must be called
+// on every use rather than stored.
+func BotUsers() *BotUserConfig {
+	return botUserConfig.Load()
+}
 
 // BotNodeOptions holds per-node options stored in bot_node_config.json. The
 // file is auto-populated by the node tracker for every node Komari reports;
@@ -238,6 +263,18 @@ type BotNodeOptions struct {
 // options.
 type BotNodeMembers map[string]BotNodeOptions
 
-// C_botNodeConfig is the global singleton mirroring bot_node_config.json,
-// populated by LoadBotNodeConfig.
-var C_botNodeConfig BotNodeMembers
+// botNodeConfig mirrors bot_node_config.json, populated by LoadBotNodeConfig.
+// The map is rebuilt rather than mutated on every load, so the pointer can be
+// swapped atomically; read it through BotNodes.
+var botNodeConfig atomic.Pointer[BotNodeMembers]
+
+// BotNodes returns the per-node options currently in effect, or nil before the
+// first LoadBotNodeConfig. Like Current it must be called on every use rather
+// than stored.
+func BotNodes() BotNodeMembers {
+	nodes := botNodeConfig.Load()
+	if nodes == nil {
+		return nil
+	}
+	return *nodes
+}