feat(bench): add macOS-only FibFlamegraphBenchmark

Exists solely to exercise CodSpeed's flamegraph symbolization on
codspeed-macro runners. Gated to macOS via a Gradle excludes rule so the
Linux/Windows matrix jobs skip it.

Author: not-matthias

examples/example-gradle/build.gradle.kts

@@ -1,3 +1,5 @@
+import org.gradle.internal.os.OperatingSystem
+
 plugins {
     java
     id("me.champeau.jmh") version "0.7.2"
@@ -30,9 +32,16 @@ jmh {
         // regex passed to JMH, so multiple entries collapse to one pattern with
         // literal commas and match nothing. Use a single alternation instead.
         includes.set(listOf(
-            ".*(SleepBenchmark|BacktrackingBenchmark|FibBenchmark).*",
+            ".*(SleepBenchmark|BacktrackingBenchmark|FibBenchmark|FibFlamegraphBenchmark).*",
         ))
     }
+
+    // FibFlamegraphBenchmark exists only to exercise the macOS flamegraph
+    // pipeline on codspeed-macro runners. Skip it on Linux/Windows so the
+    // cross-platform jobs don't run a redundant fib variant.
+    if (!OperatingSystem.current().isMacOsX) {
+        excludes.add(".*FibFlamegraphBenchmark.*")
+    }
 }
 
 sourceSets {

examples/example-gradle/src/jmh/java/bench/FibFlamegraphBenchmark.java

@@ -0,0 +1,27 @@
+package bench;
+
+import java.util.concurrent.TimeUnit;
+import org.openjdk.jmh.annotations.*;
+
+/**
+ * macOS-only benchmark whose recursion shape produces an easily-recognisable flamegraph. Gated to
+ * macOS via Gradle excludes in {@code build.gradle.kts}.
+ */
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@State(Scope.Benchmark)
+public class FibFlamegraphBenchmark {
+
+  @Param({"35"})
+  private int n;
+
+  @Benchmark
+  public long fib() {
+    return fib(n);
+  }
+
+  private static long fib(int n) {
+    if (n <= 1) return n;
+    return fib(n - 1) + fib(n - 2);
+  }
+}