refactor: #85 T5 extrait le domaine search vers backend/routers + executor partage (comportement inchange)

backend/search_executor.py

@@ -0,0 +1,35 @@
+"""Shared thread pool for CPU-bound search (ROADMAP #85, tranche 5).
+
+Holder extrait de :mod:`backend.main` sans changement de comportement :
+un seul pool (2 workers, préfixe ``"search"``) créé au démarrage et arrêté
+à l'extinction par le lifespan de ``main``. Les routers et les endpoints
+restants y accèdent via :func:`get_search_executor` au lieu du global de
+``main`` (plus d'import circulaire potentiel).
+"""
+
+from __future__ import annotations
+
+from concurrent.futures import ThreadPoolExecutor
+
+_executor: ThreadPoolExecutor | None = None
+
+
+def init_search_executor(max_workers: int = 2) -> ThreadPoolExecutor:
+    """Create (or reuse) the shared search thread pool."""
+    global _executor
+    if _executor is None:
+        _executor = ThreadPoolExecutor(max_workers=max_workers, thread_name_prefix="search")
+    return _executor
+
+
+def shutdown_search_executor() -> None:
+    """Stop the shared search thread pool (best-effort, non-blocking)."""
+    global _executor
+    if _executor is not None:
+        _executor.shutdown(wait=False)
+        _executor = None
+
+
+def get_search_executor() -> ThreadPoolExecutor | None:
+    """Return the shared search thread pool (``None`` before startup)."""
+    return _executor