Initial commit: Go SRE interview exercises

Includes solved 02-worker-pool and 09-safe-counter (mutex, atomic, sharded).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GbnJj9ZqEx9nUvzkjdwfMq

10-gotchas/ex10-goroutine-leak/main.go

@@ -0,0 +1,32 @@
+// SPOT THE LEAK. Run it — it prints goroutine counts. Explain why the number
+// grows, then fix it with a one-character-ish change.
+package main
+
+import (
+	"errors"
+	"fmt"
+	"runtime"
+	"time"
+)
+
+func fetch() (string, error) {
+	ch := make(chan string)
+	go func() {
+		time.Sleep(50 * time.Millisecond) // pretend slow upstream
+		ch <- "body"
+	}()
+	select {
+	case body := <-ch:
+		return body, nil
+	case <-time.After(10 * time.Millisecond): // timeout fires first
+		return "", errors.New("timeout")
+	}
+}
+
+func main() {
+	for i := 0; i < 100; i++ {
+		fetch()
+	}
+	time.Sleep(200 * time.Millisecond)
+	fmt.Println("goroutines still alive:", runtime.NumGoroutine()) // expected: 1
+}