ax(mining): rename RateLimiter.mu to mutex; fix prose comment to usage example

AX Principle 1 (predictable names): `mu` abbreviates `mutex` — rename to `mutex`.
AX Principle 2 (comments as usage examples): struct doc was prose ("provides token
bucket rate limiting per IP address") — replace with concrete call examples.

Co-Authored-By: Charon <charon@lethean.io>

pkg/mining/ratelimiter.go

@@ -8,12 +8,13 @@ import (
 	"github.com/gin-gonic/gin"
 )
 
-// RateLimiter provides token bucket rate limiting per IP address
+// rl := NewRateLimiter(10, 20) // 10 req/s, burst 20
+// router.Use(rl.Middleware())
 type RateLimiter struct {
 	requestsPerSecond int
 	burst             int
 	clients           map[string]*rateLimitClient
-	mu                sync.RWMutex
+	mutex             sync.RWMutex
 	stopChan          chan struct{}
 	stopped           bool
 }
@@ -56,8 +57,8 @@ func (rl *RateLimiter) cleanupLoop() {
 
 // rl.cleanup()  // called every minute by cleanupLoop; evicts IPs idle for >5 minutes
 func (rl *RateLimiter) cleanup() {
-	rl.mu.Lock()
-	defer rl.mu.Unlock()
+	rl.mutex.Lock()
+	defer rl.mutex.Unlock()
 
 	for ip, client := range rl.clients {
 		if time.Since(client.lastCheck) > 5*time.Minute {
@@ -68,8 +69,8 @@ func (rl *RateLimiter) cleanup() {
 
 // rl.Stop()  // call on shutdown to release the cleanup goroutine
 func (rl *RateLimiter) Stop() {
-	rl.mu.Lock()
-	defer rl.mu.Unlock()
+	rl.mutex.Lock()
+	defer rl.mutex.Unlock()
 
 	if !rl.stopped {
 		close(rl.stopChan)
@@ -82,7 +83,7 @@ func (rl *RateLimiter) Middleware() gin.HandlerFunc {
 	return func(c *gin.Context) {
 		ip := c.ClientIP()
 
-		rl.mu.Lock()
+		rl.mutex.Lock()
 		client, exists := rl.clients[ip]
 		if !exists {
 			client = &rateLimitClient{tokens: float64(rl.burst), lastCheck: time.Now()}
@@ -99,7 +100,7 @@ func (rl *RateLimiter) Middleware() gin.HandlerFunc {
 		client.lastCheck = now
 
 		if client.tokens < 1 {
-			rl.mu.Unlock()
+			rl.mutex.Unlock()
 			respondWithError(c, http.StatusTooManyRequests, "RATE_LIMITED",
 				"too many requests", "rate limit exceeded")
 			c.Abort()
@@ -107,14 +108,14 @@ func (rl *RateLimiter) Middleware() gin.HandlerFunc {
 		}
 
 		client.tokens--
-		rl.mu.Unlock()
+		rl.mutex.Unlock()
 		c.Next()
 	}
 }
 
 // if rl.ClientCount() == 0 { /* no active clients */ }
 func (rl *RateLimiter) ClientCount() int {
-	rl.mu.RLock()
-	defer rl.mu.RUnlock()
+	rl.mutex.RLock()
+	defer rl.mutex.RUnlock()
 	return len(rl.clients)
 }