Initial release of the oVirt/RHV Engine API simulator.

Stateful FastAPI lab with contract packs, Compose/Helm, Docker Hub release
targets, and Pulumi coverage across all Engine series (GET/POST/PUT/DELETE/HEAD).

app/db/primitives.py

@@ -0,0 +1,94 @@
+"""Typed transactional helpers and stable database error mapping."""
+
+from __future__ import annotations
+
+import asyncio
+from collections.abc import AsyncIterator, Awaitable, Callable
+from contextlib import asynccontextmanager
+from dataclasses import dataclass
+
+import asyncpg  # type: ignore[import-untyped]
+from asyncpg import Connection, Pool
+
+
+class DatabaseOperationError(RuntimeError):
+    """Safe base error for repository operations."""
+
+
+class ConflictError(DatabaseOperationError):
+    pass
+
+
+class ReferenceError(DatabaseOperationError):
+    pass
+
+
+class TransientDatabaseError(DatabaseOperationError):
+    pass
+
+
+def map_database_error(error: asyncpg.PostgresError) -> DatabaseOperationError:
+    if isinstance(error, asyncpg.UniqueViolationError):
+        return ConflictError("database uniqueness constraint failed")
+    if isinstance(error, asyncpg.ForeignKeyViolationError):
+        return ReferenceError("database reference constraint failed")
+    if isinstance(
+        error,
+        asyncpg.SerializationError
+        | asyncpg.DeadlockDetectedError
+        | asyncpg.TooManyConnectionsError,
+    ):
+        return TransientDatabaseError("transient database failure")
+    return DatabaseOperationError("database operation failed")
+
+
+@asynccontextmanager
+async def transaction(pool: Pool) -> AsyncIterator[Connection]:
+    async with pool.acquire() as connection:
+        try:
+            async with connection.transaction():
+                yield connection
+        except asyncpg.PostgresError as error:
+            raise map_database_error(error) from error
+
+
+@asynccontextmanager
+async def savepoint(connection: Connection) -> AsyncIterator[Connection]:
+    try:
+        async with connection.transaction():
+            yield connection
+    except asyncpg.PostgresError as error:
+        raise map_database_error(error) from error
+
+
+def require_affected(status: str, expected: int = 1) -> None:
+    try:
+        affected = int(status.rsplit(" ", 1)[1])
+    except (IndexError, ValueError) as error:
+        raise DatabaseOperationError(f"unrecognized command status: {status}") from error
+    if affected != expected:
+        raise DatabaseOperationError(f"expected {expected} affected row(s), got {affected}")
+
+
+@dataclass(frozen=True, slots=True)
+class RetryPolicy:
+    attempts: int = 3
+    base_delay_seconds: float = 0.02
+
+
+DEFAULT_RETRY_POLICY = RetryPolicy()
+
+
+async def retry_transient[T](
+    operation: Callable[[], Awaitable[T]], policy: RetryPolicy = DEFAULT_RETRY_POLICY
+) -> T:
+    if policy.attempts < 1:
+        raise ValueError("retry attempts must be positive")
+    for attempt in range(policy.attempts):
+        try:
+            return await operation()
+        except TransientDatabaseError:
+            if attempt + 1 == policy.attempts:
+                raise
+            await asyncio.sleep(policy.base_delay_seconds * (2**attempt))
+    raise RuntimeError("unreachable retry state")