feat(dataset-builder): add retry logic and ASCII-safe logging for Siemens PDF pipeline

- question_generator.py: add max_retries=3/retry_delay=5s loop with
  exponential backoff on LLM timeout or server errors; encode filenames
  with ascii/replace before printing to avoid UnicodeEncodeError on
  Windows cp1252 consoles
- runner.py: encode PDF filenames ASCII-safe for progress messages;
  catch generation failures per-document and skip (or re-raise) based
  on failure_mode, preventing one bad doc from aborting the whole build

Co-Authored-By: Claude Opus 4 <noreply@anthropic.com>

rag_eval/dataset_builder/generator/question_generator.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import json
+import time
 from abc import ABC, abstractmethod
 from typing import Any
 
@@ -150,24 +151,39 @@ class OpenAIQuestionGenerator(QuestionGenerator):
         max_questions: int,
         max_chunks_per_question: int,
         job_name: str,
+        max_retries: int = 3,
+        retry_delay: float = 5.0,
     ) -> list[DraftQuestionSample]:
-        """Generate draft questions for one parsed document."""
+        """Generate draft questions for one parsed document, with retry on timeout/server errors."""
         prompt = self._build_prompt(
             document,
             max_questions=max_questions,
             max_chunks_per_question=max_chunks_per_question,
         )
-        response = self.client.chat.completions.create(
-            model=self.model,
-            messages=[
-                {"role": "system", "content": "You generate structured draft question banks from source documents."},
-                {"role": "user", "content": prompt},
-            ],
-            response_format={"type": "json_object"},
-        )
-        content = response.choices[0].message.content or "{}"
-        payload = self._parse_response_payload(content)
-        return [
-            self._build_sample(document=document, payload=item, index=index, job_name=job_name)
-            for index, item in enumerate(payload[:max_questions], start=1)
-        ]
+        last_exc: Exception | None = None
+        for attempt in range(1, max_retries + 1):
+            try:
+                response = self.client.chat.completions.create(
+                    model=self.model,
+                    messages=[
+                        {"role": "system", "content": "You generate structured draft question banks from source documents."},
+                        {"role": "user", "content": prompt},
+                    ],
+                    response_format={"type": "json_object"},
+                )
+                content = response.choices[0].message.content or "{}"
+                payload = self._parse_response_payload(content)
+                return [
+                    self._build_sample(document=document, payload=item, index=index, job_name=job_name)
+                    for index, item in enumerate(payload[:max_questions], start=1)
+                ]
+            except Exception as exc:
+                last_exc = exc
+                if attempt < max_retries:
+                    wait = retry_delay * attempt
+                    doc_name_safe = document.doc_name.encode("ascii", "replace").decode("ascii")
+                    print(f"  [warn] generate attempt {attempt}/{max_retries} failed for {doc_name_safe!r}: {exc}. Retrying in {wait:.0f}s...")
+                    time.sleep(wait)
+        raise RuntimeError(
+            f"Question generation failed for {document.doc_name!r} after {max_retries} attempts"
+        ) from last_exc