missed this

Signed-off-by: Robert Kruszewski <github@robertk.io>

Author: robert3005

vortex-array/src/optimizer/session.rs

@@ -0,0 +1,43 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: Copyright the Vortex contributors
+
+//! Session state for pluggable parent-reduce rules.
+//!
+//! [`OptimizerSession`] wraps an [`FnRegistry`] keyed by `(parent_encoding_id, child_encoding_id)`
+//! and is consulted by the optimizer during execution, before the child encoding's static
+//! `PARENT_RULES` are tried. Entries are typed as [`ReduceParentFn`](super::ReduceParentFn).
+//!
+//! The registry is empty by default. Downstream crates register `ReduceParentFn` values to add
+//! new parent-reduce rules or override ones that the child encoding would otherwise run from its
+//! static `PARENT_RULES`.
+
+use vortex_session::Ref;
+use vortex_session::SessionExt;
+use vortex_session::registry::FnRegistry;
+
+/// Session state for pluggable parent-reduce dispatch keyed by `(parent_id, child_id)`.
+#[derive(Debug, Default)]
+pub struct OptimizerSession {
+    registry: FnRegistry,
+}
+
+impl OptimizerSession {
+    /// Create an empty session with no rules registered.
+    pub fn empty() -> Self {
+        Self::default()
+    }
+
+    /// Access the underlying registry for direct registration and lookup.
+    pub fn registry(&self) -> &FnRegistry {
+        &self.registry
+    }
+}
+
+/// Extension trait for accessing the optimizer registry from a Vortex session.
+pub trait OptimizerSessionExt: SessionExt {
+    /// Returns the optimizer session variable.
+    fn optimizer(&self) -> Ref<'_, OptimizerSession> {
+        self.get::<OptimizerSession>()
+    }
+}
+impl<S: SessionExt> OptimizerSessionExt for S {}