Remove unused LOG fields, use newSingleThreadExecutor for Java 21 overlay, fix empty docs section

Agent-Logs-Url: https://github.com/github/copilot-sdk-java/sessions/46706dd3-402c-41c9-9150-3cfae7db8c3f

Co-authored-by: brunoborges <129743+brunoborges@users.noreply.github.com>

Author: Copilot

src/main/java/com/github/copilot/sdk/ThreadFactoryProvider.java

@@ -6,7 +6,6 @@
 
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
-import java.util.logging.Logger;
 
 /**
  * Provides thread factories for the SDK's internal thread creation.
@@ -24,8 +23,6 @@
  */
 final class ThreadFactoryProvider {
 
-    private static final Logger LOG = Logger.getLogger(ThreadFactoryProvider.class.getName());
-
     private ThreadFactoryProvider() {
     }
 

src/main/java21/com/github/copilot/sdk/ThreadFactoryProvider.java

@@ -6,7 +6,6 @@
 
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
-import java.util.logging.Logger;
 
 /**
  * Java 21+ override that uses virtual threads for the SDK's internal thread
@@ -20,8 +19,6 @@
  */
 final class ThreadFactoryProvider {
 
-    private static final Logger LOG = Logger.getLogger(ThreadFactoryProvider.class.getName());
-
     private ThreadFactoryProvider() {
     }
 

src/site/markdown/advanced.md

@@ -1262,12 +1262,7 @@ The SDK JAR includes `Multi-Release: true` in its manifest. On Java 21+, the JVM
 
 ### Verifying Virtual Thread Usage
 
-You can check at runtime whether the SDK is using virtual threads:
-
-```java
-// Thread names are preserved for debuggability regardless of thread type.
-// On Java 21+, the jsonrpc-reader and cli-stderr-reader threads will be virtual.
-```
+Thread names are preserved for debuggability regardless of thread type. On Java 21+, a thread dump will show `jsonrpc-reader` and `cli-stderr-reader` as virtual threads rather than platform threads. You can verify this via `jcmd <pid> Thread.dump_to_file -format=json <file>` or your IDE's thread inspector.
 
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