Fix CodeQL always-true comparison and string identity alerts

- SessionEventsE2ETest: replace trivially-true size >= 0 assertion with
  conditional content access (getData() assertion when events present).
- InProcessEnvGuard: suppress StringEquality warning on intentional
  identity comparison with ABSENT_SENTINEL (unique instance used as a
  null-alternative sentinel to distinguish absent vs empty env vars).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: c4e523e3-9d39-4598-90ec-54d959c44ce8

Author: edburns

java/sdk/src/test/java/com/github/copilot/SessionEventsE2ETest.java

@@ -5,6 +5,7 @@
 package com.github.copilot;
 
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.nio.file.Files;
@@ -184,8 +185,9 @@ void testShouldReceiveSessionEvents_assistantUsageEvent() throws Exception {
             // Usage events may or may not be emitted depending on the model/API version
             // This test verifies the event handler works when they are emitted
             // We don't assert they must be present since it depends on the backend
-            assertTrue(usageEvents.size() >= 0,
-                    "Usage event handler should not throw (collected " + usageEvents.size() + " events)");
+            if (!usageEvents.isEmpty()) {
+                assertNotNull(usageEvents.get(0).getData(), "Usage event should carry data");
+            }
         }
     }
 

java/sdk/src/test/java/com/github/copilot/ffi/InProcessEnvGuard.java

@@ -120,7 +120,11 @@ public void close() {
         List<Map.Entry<String, String>> reversed = new ArrayList<>(saved);
         Collections.reverse(reversed);
         for (Map.Entry<String, String> entry : reversed) {
-            String restoreValue = entry.getValue() == ABSENT_SENTINEL ? null : entry.getValue();
+            // Identity comparison is intentional: ABSENT_SENTINEL is a unique instance
+            // used to distinguish "env var was absent" from "env var was empty string".
+            @SuppressWarnings("StringEquality")
+            boolean wasAbsent = entry.getValue() == ABSENT_SENTINEL;
+            String restoreValue = wasAbsent ? null : entry.getValue();
             nativeSetEnv(entry.getKey(), restoreValue);
         }
     }