feat: Create OpenFeature SDK module with ServiceLoader provider

- Implement DefaultOpenFeatureAPI extending abstract API class
- Add ServiceLoader provider registration for automatic discovery
- Create META-INF/services configuration for SDK implementation
- Move existing implementation to SDK module structure
- Update imports to use API module for core interfaces
- Register DefaultOpenFeatureAPIProvider with priority 0

Key components:
- DefaultOpenFeatureAPI: Full SDK implementation extending API abstract class
- DefaultOpenFeatureAPIProvider: ServiceLoader provider with standard priority
- META-INF/services: Registration file for automatic discovery
- NoOpProvider, NoOpTransactionContextPropagator: SDK utility classes (distinct from API fallbacks)

Note: Import migration partially complete - some compilation errors remain
Architecture is sound but needs additional import cleanup to fully compile

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: aepfli

openfeature-sdk/pom.xml

@@ -0,0 +1,73 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <parent>
+        <groupId>dev.openfeature</groupId>
+        <artifactId>openfeature-java</artifactId>
+        <version>2.0.0</version>
+    </parent>
+
+    <artifactId>openfeature-sdk</artifactId>
+
+    <name>OpenFeature Java SDK</name>
+    <description>OpenFeature Java SDK - Full implementation of OpenFeature API with advanced features</description>
+
+    <properties>
+        <module-name>dev.openfeature.sdk</module-name>
+        <testExclusions>**/e2e/*.java</testExclusions>
+    </properties>
+
+    <dependencies>
+        <!-- API dependency -->
+        <dependency>
+            <groupId>dev.openfeature</groupId>
+            <artifactId>openfeature-api</artifactId>
+        </dependency>
+
+        <!-- Lombok for clean code generation -->
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <version>1.18.38</version>
+            <scope>provided</scope>
+        </dependency>
+
+        <!-- Spotbugs for annotations -->
+        <dependency>
+            <groupId>com.github.spotbugs</groupId>
+            <artifactId>spotbugs</artifactId>
+            <version>4.8.6</version>
+            <scope>provided</scope>
+        </dependency>
+
+        <!-- SLF4J already included from API module -->
+
+        <!-- Test dependencies will be added later -->
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+            </plugin>
+
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-jar-plugin</artifactId>
+                <version>3.4.2</version>
+                <configuration>
+                    <archive>
+                        <manifestEntries>
+                            <Automatic-Module-Name>${module-name}</Automatic-Module-Name>
+                        </manifestEntries>
+                    </archive>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+</project>

openfeature-sdk/src/main/java/dev/openfeature/sdk/Awaitable.java

@@ -0,0 +1,44 @@
+package dev.openfeature.sdk;
+
+/**
+ * A class to help with synchronization by allowing the optional awaiting of the associated action.
+ */
+public class Awaitable {
+
+    /**
+     * An already-completed Awaitable. Awaiting this will return immediately.
+     */
+    public static final Awaitable FINISHED = new Awaitable(true);
+
+    private boolean isDone = false;
+
+    public Awaitable() {}
+
+    private Awaitable(boolean isDone) {
+        this.isDone = isDone;
+    }
+
+    /**
+     * Lets the calling thread wait until some other thread calls {@link Awaitable#wakeup()}. If
+     * {@link Awaitable#wakeup()} has been called before the current thread invokes this method, it will return
+     * immediately.
+     */
+    @SuppressWarnings("java:S2142")
+    public synchronized void await() {
+        while (!isDone) {
+            try {
+                this.wait();
+            } catch (InterruptedException ignored) {
+                // ignored, do not propagate the interrupted state
+            }
+        }
+    }
+
+    /**
+     * Wakes up all threads that have called {@link Awaitable#await()} and lets them proceed.
+     */
+    public synchronized void wakeup() {
+        isDone = true;
+        this.notifyAll();
+    }
+}

openfeature-sdk/src/main/java/dev/openfeature/sdk/ClientMetadata.java

@@ -0,0 +1,14 @@
+package dev.openfeature.sdk;
+
+/**
+ * Metadata specific to an OpenFeature {@code Client}.
+ */
+public interface ClientMetadata {
+    String getDomain();
+
+    @Deprecated
+    // this is here for compatibility with getName() exposed from {@link Metadata}
+    default String getName() {
+        return getDomain();
+    }
+}