chore: import upstream snapshot with attribution

python/mirage/runtime/session_context.py

@@ -0,0 +1,71 @@
+# ========= Copyright 2026 @ Strukto.AI All Rights Reserved. =========
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ========= Copyright 2026 @ Strukto.AI All Rights Reserved. =========
+
+from contextvars import ContextVar, Token
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from mirage.workspace.session.session import Session
+
+_current_session: ContextVar["Session | None"] = ContextVar(
+    "mirage_current_session",
+    default=None,
+)
+
+
+def set_current_session(session: "Session | None") -> Token:
+    """Bind ``session`` to the current async context."""
+    return _current_session.set(session)
+
+
+def reset_current_session(token: Token) -> None:
+    """Restore the previous session binding."""
+    _current_session.reset(token)
+
+
+def get_current_session() -> "Session | None":
+    """Return the session bound to the current async context, if any."""
+    return _current_session.get()
+
+
+def assert_mount_allowed(mount_prefix: str) -> None:
+    """Raise PermissionError if the current session may not touch this mount.
+
+    No-op when no session is bound or the session is unrestricted
+    (``allowed_mounts is None``). The session's ``allowed_mounts`` is
+    expected to already include any infrastructure prefixes (observer,
+    ``/dev``) added at session-creation time.
+
+    Args:
+        mount_prefix (str): the mount's prefix, e.g. ``/s3`` or ``/`` for the
+            cache root.
+
+    Raises:
+        PermissionError: the mount lies outside the session's allowlist.
+    """
+    sess = _current_session.get()
+    if sess is None or sess.allowed_mounts is None:
+        return
+    norm = "/" + mount_prefix.strip("/") if mount_prefix.strip("/") else "/"
+    # A user-defined root mount ({"/": resource}) currently bypasses
+    # the allowlist entirely. This is an undocumented escape hatch: a
+    # session restricted to /s3 but with a workspace mounted at root
+    # would still expose every path under /. Behaviour-changing fix is
+    # out of scope for this refactor, flagged for separate discussion.
+    if norm == "/":
+        return
+    if norm in sess.allowed_mounts:
+        return
+    raise PermissionError(
+        f"session {sess.session_id!r} not allowed to access mount {norm!r}")