Debugging: Verbesserte Fehlerdiagnose für Saxon Worker Pool

- Leitet stderr jedes Workers in separate Log-Dateien um (worker_N_stderr.log)
- Fügt Startup-Health-Check hinzu: Prüft nach 100ms ob Worker noch läuft
- Fügt Pre-Transform-Check hinzu: Validiert Worker-Status vor jedem Job
- Zeigt stderr-Inhalt in Fehlermeldungen wenn Worker crashen
- Erweitert Debug-Logging für Job-Submission und Worker-Antworten

Dies hilft, die Ursache der "broken pipe" Fehler zu identifizieren.

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/saxon_pool.py

@@ -207,11 +207,15 @@ class SaxonWorkerPool:
                 # Starte JVM-Prozess mit SaxonWorker
                 cmd = [str(self.java_vm_path), "-cp", full_classpath, "SaxonWorker"]
 
+                # Öffne stderr-Log-Datei für diesen Worker
+                stderr_log = self.temp_dir / f"worker_{i}_stderr.log"
+                stderr_file = open(stderr_log, "w", encoding="utf-8")
+
                 process = subprocess.Popen(
                     cmd,
                     stdin=subprocess.PIPE,
                     stdout=subprocess.PIPE,
-                    stderr=subprocess.PIPE,
+                    stderr=stderr_file,  # Redirect stderr to file
                     text=True,
                     bufsize=1,  # Line buffered
                 )
@@ -219,7 +223,22 @@ class SaxonWorkerPool:
                 self.workers.append(process)
                 self.worker_locks.append(threading.Lock())
 
-                logger.debug(f"Worker {i} gestartet (PID: {process.pid})")
+                logger.debug(f"Worker {i} gestartet (PID: {process.pid}, stderr: {stderr_log})")
+
+                # Warte kurz damit Worker initialisieren kann
+                import time
+
+                time.sleep(0.1)
+
+                # Prüfe ob Worker noch läuft
+                if process.poll() is not None:
+                    # Worker ist bereits beendet - Fehler!
+                    stderr_file.close()
+                    with open(stderr_log, "r") as f:
+                        stderr_content = f.read()
+                    raise RuntimeError(
+                        f"Worker {i} ist sofort beendet (Exit Code: {process.returncode})\nstderr:\n{stderr_content}"
+                    )
 
             except Exception as e:
                 logger.error(f"Fehler beim Starten von Worker {i}: {e}")
@@ -259,12 +278,29 @@ class SaxonWorkerPool:
         try:
             worker = self.workers[worker_idx]
 
+            # Prüfe ob Worker noch läuft
+            if worker.poll() is not None:
+                # Worker ist tot!
+                stderr_log = self.temp_dir / f"worker_{worker_idx}_stderr.log"
+                try:
+                    with open(stderr_log, "r") as f:
+                        stderr_content = f.read()
+                    error_msg = (
+                        f"Worker {worker_idx} ist beendet (Exit: {worker.returncode})\nstderr:\n{stderr_content}"
+                    )
+                except Exception:
+                    error_msg = f"Worker {worker_idx} ist beendet (Exit: {worker.returncode})"
+                logger.error(error_msg)
+                return False, error_msg
+
             # Formatiere Parameter
             params_str = "|||".join([f"{key}={value}" for key, value in xslt_params.items()])
 
             # Erstelle Job-String (Tab-separated)
             job = f"{source_xml}\t{xsl_stylesheet}\t{output_fo}\t{params_str}\n"
 
+            logger.debug(f"Sende Job an Worker {worker_idx}: {source_xml.name}")
+
             # Sende Job an Worker
             worker.stdin.write(job)
             worker.stdin.flush()
@@ -272,12 +308,23 @@ class SaxonWorkerPool:
             # Warte auf Antwort
             response = worker.stdout.readline().strip()
 
+            logger.debug(f"Worker {worker_idx} Antwort: '{response}'")
+
             if response == "OK":
                 return True, "Erfolgreich"
             elif response.startswith("ERROR:"):
                 error_msg = response[6:].strip()
                 return False, f"Saxon-Fehler: {error_msg}"
             else:
+                # Leere Antwort bedeutet Worker ist crashed
+                if not response:
+                    stderr_log = self.temp_dir / f"worker_{worker_idx}_stderr.log"
+                    try:
+                        with open(stderr_log, "r") as f:
+                            stderr_content = f.read()[-500:]  # Letzte 500 Zeichen
+                        return False, f"Worker {worker_idx} crashed (keine Antwort)\nstderr:\n{stderr_content}"
+                    except Exception:
+                        return False, f"Worker {worker_idx} crashed (keine Antwort)"
                 return False, f"Unerwartete Antwort: {response}"
 
         except Exception as e: