Backend su file SQLite locale: DB_URL, PRAGMA FK/WAL, UPLOAD_DIR assoluto (TieMeasureFlow#77)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/backend/database.py

@@ -1,6 +1,7 @@
 """Async SQLAlchemy database engine and session management."""
 from collections.abc import AsyncGenerator
 
+from sqlalchemy import event
 from sqlalchemy.ext.asyncio import (
     AsyncSession,
     async_sessionmaker,
@@ -10,14 +11,30 @@ from sqlalchemy.orm import DeclarativeBase
 
 from src.backend.config import settings
 
-# Create async engine
-engine = create_async_engine(
-    settings.database_url,
-    echo=False,
-    pool_size=10,
-    max_overflow=20,
-    pool_recycle=3600,
-)
+_IS_SQLITE = settings.database_url.startswith("sqlite")
+
+# Create async engine. MySQL gets a connection pool; SQLite (local file of the
+# Windows package) does not accept pool_size/max_overflow/pool_recycle.
+if _IS_SQLITE:
+    engine = create_async_engine(settings.database_url, echo=False)
+
+    @event.listens_for(engine.sync_engine, "connect")
+    def _sqlite_pragmas(dbapi_connection, _connection_record) -> None:
+        """Per-connection PRAGMAs: SQLite ignores FKs unless asked, and WAL +
+        busy_timeout let the web, vision and backend threads share the file."""
+        cursor = dbapi_connection.cursor()
+        cursor.execute("PRAGMA foreign_keys=ON")
+        cursor.execute("PRAGMA journal_mode=WAL")
+        cursor.execute("PRAGMA busy_timeout=5000")
+        cursor.close()
+else:
+    engine = create_async_engine(
+        settings.database_url,
+        echo=False,
+        pool_size=10,
+        max_overflow=20,
+        pool_recycle=3600,
+    )
 
 # Session factory
 async_session_factory = async_sessionmaker(