fix(flagd): cap container pool size to avoid Docker overload

Default pool size was Runtime.availableProcessors() which on large machines
(22 CPUs) spawned too many simultaneous Docker Compose stacks and caused
ContainerLaunchException. Cap at min(availableProcessors, 4).

Cucumber threads still scale with CPUs (dynamic factor=1) — extra threads
simply block waiting for a free container, which is safe.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Signed-off-by: Simon Schrottner <simon.schrottner@dynatrace.com>

Author: aepfli

providers/flagd/src/test/java/dev/openfeature/contrib/providers/flagd/e2e/ContainerPool.java

@@ -29,8 +29,8 @@
 @Slf4j
 public class ContainerPool {
 
-    private static final int POOL_SIZE =
-            Integer.getInteger("flagd.e2e.pool.size", Runtime.getRuntime().availableProcessors());
+    private static final int POOL_SIZE = Integer.getInteger(
+            "flagd.e2e.pool.size", Math.min(Runtime.getRuntime().availableProcessors(), 4));
 
     private static final BlockingQueue<ContainerEntry> pool = new LinkedBlockingQueue<>();
     private static final List<ContainerEntry> all = new ArrayList<>();

providers/flagd/src/test/resources/junit-platform.properties

@@ -3,9 +3,9 @@
 # concurrent scenarios are fully isolated — no shared flagd process.
 cucumber.execution.parallel.enabled=true
 # Dynamic strategy scales with available CPUs (factor=1.0 → 1 thread per core).
-# ContainerPool defaults to Runtime.availableProcessors() so pool slots match.
-# Override both via -Dflagd.e2e.pool.size=N and
-# -Dcucumber.execution.parallel.config.dynamic.factor=N if needed.
+# ContainerPool caps at min(availableProcessors, 4) containers so Docker isn't
+# overwhelmed; extra threads simply block waiting for a free container.
+# Override pool size via -Dflagd.e2e.pool.size=N if needed.
 cucumber.execution.parallel.config.strategy=dynamic
 cucumber.execution.parallel.config.dynamic.factor=1
 # Scenarios tagged @env-var mutate System env vars globally.