fix(acp): prevent reader thread leak on transport close

AcpTransport.close() left the acp-reader thread blocked on readLine()
when the child process had spawned grandchildren (e.g. `sh -c "... sleep 30"`)
that inherited the stdout pipe. process.destroy() only terminates the
direct child, so the pipe stayed open and the reader never reached EOF,
causing testPing_timeout_returnsFalse to fail with a thread leak.

Close process stdout explicitly to unblock readLine, interrupt the reader
thread, and wait on destroyForcibly to ensure full cleanup.

Also de-duplicate Xvfb startup in the Tests workflow: export DISPLAY via
\$GITHUB_ENV so it persists to the Gradle step instead of starting Xvfb
twice (which logged "Server is already active for display 99").

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: stephanj

.github/workflows/tests.yml

@@ -28,7 +28,9 @@ jobs:
         run: sudo apt-get install -y xvfb
 
       - name: Start Xvfb
-        run: Xvfb :99 & export DISPLAY=:99
+        run: |
+          Xvfb :99 &
+          echo "DISPLAY=:99" >> $GITHUB_ENV
 
       - name: Run Gradle tests
         env:
@@ -40,9 +42,7 @@ jobs:
           AWS_ACCESS_KEY_ID: ${{ secrets.AWS_ACCESS_KEY_ID }}
           AWS_SECRET_ACCESS_KEY: ${{ secrets.AWS_SECRET_ACCESS_KEY }}
           AWS_REGION: ${{ secrets.AWS_REGION }}
-        run: |
-          Xvfb :99 & export DISPLAY=:99
-          ./gradlew test
+        run: ./gradlew test
 
       - name: Upload Test Reports
         if: always()

src/main/java/com/devoxx/genie/service/acp/protocol/AcpTransport.java

@@ -262,16 +262,26 @@ public void close() {
         pendingRequests.clear();
         if (process != null) {
             process.destroy();
+            // Close stdout explicitly: the child may have spawned grandchildren that
+            // inherit the pipe, leaving the reader thread blocked on readLine() even
+            // after destroy(). Closing the stream unblocks it with an IOException.
+            try {
+                process.getInputStream().close();
+            } catch (IOException ignored) {
+                // best-effort
+            }
             try {
                 if (!process.waitFor(SHUTDOWN_WAIT_SECONDS, TimeUnit.SECONDS)) {
                     process.destroyForcibly();
+                    process.waitFor(SHUTDOWN_WAIT_SECONDS, TimeUnit.SECONDS);
                 }
             } catch (InterruptedException e) {
                 Thread.currentThread().interrupt();
                 process.destroyForcibly();
             }
         }
         if (readerThread != null) {
+            readerThread.interrupt();
             try {
                 readerThread.join(TimeUnit.SECONDS.toMillis(SHUTDOWN_WAIT_SECONDS));
             } catch (InterruptedException e) {