Address Copilot review items from #4251754607

- Update class Javadoc to reflect 3 tests (was 2)
- Third test: remove misleading isReady toggling since buffering
  is triggered by readyAndDrained=false (set after first write),
  not by isReady() state. Keep isReady always true to match
  the actual scenario being tested.
- Fix comment: 'buffering happens regardless of isReady state'
- Fix inline comment in runOrBuffer flush path: 'subsequent
  writes/flushes can go direct without unnecessary buffering'

Reviewed-by: copilot-pull-request-reviewer[bot]
Fixes #12790

Author: mgustimz

servlet/src/main/java/io/grpc/servlet/AsyncServletOutputStreamWriter.java

@@ -223,8 +223,9 @@ private void runOrBuffer(ActionItem actionItem) throws IOException {
         return;
       }
       if (actionItem == flushAction) {
-        // flush path: only set readyAndDrained=false if isReady() returns false
-        // If isReady() is still true, keep readyAndDrained=true so flush goes direct
+        // flush path: only set readyAndDrained=false if isReady() returns false.
+        // If isReady() is still true, keep readyAndDrained=true so subsequent
+        // writes/flushes can go direct without unnecessary buffering.
         if (!isReady.getAsBoolean()) {
           boolean successful =
               writeState.compareAndSet(curState, curState.withReadyAndDrained(false));

servlet/src/test/java/io/grpc/servlet/AsyncServletOutputStreamWriterTest.java

@@ -32,9 +32,10 @@
 
 /**
  * Unit test for {@link AsyncServletOutputStreamWriter} with a mock isReady supplier.
- * Tests two scenarios: (1) writes with isReady always true, where onWritePossible()
- * is called between writes; (2) writes with readyAndDrained=false (triggered by first
- * write), where subsequent writes are buffered until onWritePossible() drains them.
+ * Tests three scenarios:
+ * (1) A write followed by another write without onWritePossible() is buffered.
+ * (2) Consecutive writes with onWritePossible() between them succeed.
+ * (3) When isReady() becomes false, writes are buffered until onWritePossible() drains them.
  */
 @RunWith(JUnit4.class)
 public class AsyncServletOutputStreamWriterTest {
@@ -154,9 +155,8 @@ public void writeBytes_isReadyFalse_buffersUntilOnWritePossible() throws IOExcep
     byte[] data1 = new byte[]{1};
     writer.writeBytes(data1, 1);
 
-    // After first write, readyAndDrained=false, so any subsequent write is buffered
-    isReady.set(false);
-
+    // After first write, readyAndDrained=false, so any subsequent write is buffered.
+    // This buffering happens regardless of isReady() state (the Tomcat fix).
     // Second write - should be buffered since readyAndDrained=false
     byte[] data2 = new byte[]{2};
     writer.writeBytes(data2, 1);
@@ -165,7 +165,6 @@ public void writeBytes_isReadyFalse_buffersUntilOnWritePossible() throws IOExcep
     assertEquals("First write should complete, second buffered", 1, actions.size());
 
     // Container calls onWritePossible to drain buffered writes
-    isReady.set(true);
     writer.onWritePossible();
 
     // Now both writes should have completed