diff --git a/vortex-cuda/src/layout.rs b/vortex-cuda/src/layout.rs
index 858bb87e0cc..20ab3f3a50b 100644
--- a/vortex-cuda/src/layout.rs
+++ b/vortex-cuda/src/layout.rs
@@ -180,6 +180,7 @@ impl VTable for CudaFlat {
         name: Arc<str>,
         segment_source: Arc<dyn SegmentSource>,
         session: &VortexSession,
+        _ctx: &vortex::layout::LayoutReaderContext,
     ) -> VortexResult<LayoutReaderRef> {
         Ok(Arc::new(CudaFlatReader {
             layout: layout.clone(),
diff --git a/vortex-file/src/file.rs b/vortex-file/src/file.rs
index f321d774197..b8e31f1fea2 100644
--- a/vortex-file/src/file.rs
+++ b/vortex-file/src/file.rs
@@ -90,7 +90,12 @@ impl VortexFile {
         self.footer
             .layout()
             // TODO(ngates): we may want to allow the user pass in a name here?
-            .new_reader("".into(), segment_source, &self.session)
+            .new_reader(
+                "".into(),
+                segment_source,
+                &self.session,
+                &Default::default(),
+            )
     }
 
     /// Create a [`DataSource`](vortex_scan::DataSource) from this file for scanning.
diff --git a/vortex-file/src/v2/file_stats_reader.rs b/vortex-file/src/v2/file_stats_reader.rs
index f65c758ee7d..bdb104ddabb 100644
--- a/vortex-file/src/v2/file_stats_reader.rs
+++ b/vortex-file/src/v2/file_stats_reader.rs
@@ -310,7 +310,7 @@ mod tests {
                 )
                 .await?;
 
-            let child = layout.new_reader("".into(), segments, &SESSION)?;
+            let child = layout.new_reader("".into(), segments, &SESSION, &Default::default())?;
 
             let reader =
                 FileStatsLayoutReader::new(child, test_file_stats(0, 100), SESSION.clone());
@@ -349,7 +349,7 @@ mod tests {
                 )
                 .await?;
 
-            let child = layout.new_reader("".into(), segments, &SESSION)?;
+            let child = layout.new_reader("".into(), segments, &SESSION, &Default::default())?;
 
             let reader =
                 FileStatsLayoutReader::new(child, test_file_stats(0, 100), SESSION.clone());
@@ -400,7 +400,7 @@ mod tests {
                 )
                 .await?;
 
-            let child = layout.new_reader("".into(), segments, &SESSION)?;
+            let child = layout.new_reader("".into(), segments, &SESSION, &Default::default())?;
 
             // File-level stats: 1 null in deleted_at.
             let mut stats = StatsSet::default();
@@ -449,7 +449,7 @@ mod tests {
                 )
                 .await?;
 
-            let child = layout.new_reader("".into(), segments, &SESSION)?;
+            let child = layout.new_reader("".into(), segments, &SESSION, &Default::default())?;
 
             let reader =
                 FileStatsLayoutReader::new(child, test_file_null_count_stats(5), SESSION.clone());
diff --git a/vortex-layout/public-api.lock b/vortex-layout/public-api.lock
index 1c6ae70dd6f..f82986026c9 100644
--- a/vortex-layout/public-api.lock
+++ b/vortex-layout/public-api.lock
@@ -90,7 +90,7 @@ pub fn vortex_layout::layouts::chunked::Chunked::metadata(&Self::Layout) -> Self
 
 pub fn vortex_layout::layouts::chunked::Chunked::nchildren(&Self::Layout) -> usize
 
-pub fn vortex_layout::layouts::chunked::Chunked::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
+pub fn vortex_layout::layouts::chunked::Chunked::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession, &vortex_layout::LayoutReaderContext) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
 
 pub fn vortex_layout::layouts::chunked::Chunked::row_count(&Self::Layout) -> u64
 
@@ -308,7 +308,7 @@ pub fn vortex_layout::layouts::dict::Dict::metadata(&Self::Layout) -> Self::Meta
 
 pub fn vortex_layout::layouts::dict::Dict::nchildren(&Self::Layout) -> usize
 
-pub fn vortex_layout::layouts::dict::Dict::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
+pub fn vortex_layout::layouts::dict::Dict::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession, &vortex_layout::LayoutReaderContext) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
 
 pub fn vortex_layout::layouts::dict::Dict::row_count(&Self::Layout) -> u64
 
@@ -474,7 +474,7 @@ pub fn vortex_layout::layouts::flat::Flat::metadata(&Self::Layout) -> Self::Meta
 
 pub fn vortex_layout::layouts::flat::Flat::nchildren(&Self::Layout) -> usize
 
-pub fn vortex_layout::layouts::flat::Flat::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
+pub fn vortex_layout::layouts::flat::Flat::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession, &vortex_layout::LayoutReaderContext) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
 
 pub fn vortex_layout::layouts::flat::Flat::row_count(&Self::Layout) -> u64
 
@@ -674,7 +674,7 @@ pub fn vortex_layout::layouts::struct_::Struct::metadata(&Self::Layout) -> Self:
 
 pub fn vortex_layout::layouts::struct_::Struct::nchildren(&Self::Layout) -> usize
 
-pub fn vortex_layout::layouts::struct_::Struct::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
+pub fn vortex_layout::layouts::struct_::Struct::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession, &vortex_layout::LayoutReaderContext) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
 
 pub fn vortex_layout::layouts::struct_::Struct::row_count(&Self::Layout) -> u64
 
@@ -838,7 +838,7 @@ pub fn vortex_layout::layouts::zoned::Zoned::metadata(&Self::Layout) -> Self::Me
 
 pub fn vortex_layout::layouts::zoned::Zoned::nchildren(&Self::Layout) -> usize
 
-pub fn vortex_layout::layouts::zoned::Zoned::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
+pub fn vortex_layout::layouts::zoned::Zoned::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession, &vortex_layout::LayoutReaderContext) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
 
 pub fn vortex_layout::layouts::zoned::Zoned::row_count(&Self::Layout) -> u64
 
@@ -1456,7 +1456,7 @@ pub fn vortex_layout::vtable::VTable::metadata(&Self::Layout) -> Self::Metadata
 
 pub fn vortex_layout::vtable::VTable::nchildren(&Self::Layout) -> usize
 
-pub fn vortex_layout::vtable::VTable::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
+pub fn vortex_layout::vtable::VTable::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession, &vortex_layout::LayoutReaderContext) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
 
 pub fn vortex_layout::vtable::VTable::row_count(&Self::Layout) -> u64
 
@@ -1488,7 +1488,7 @@ pub fn vortex_layout::layouts::chunked::Chunked::metadata(&Self::Layout) -> Self
 
 pub fn vortex_layout::layouts::chunked::Chunked::nchildren(&Self::Layout) -> usize
 
-pub fn vortex_layout::layouts::chunked::Chunked::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
+pub fn vortex_layout::layouts::chunked::Chunked::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession, &vortex_layout::LayoutReaderContext) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
 
 pub fn vortex_layout::layouts::chunked::Chunked::row_count(&Self::Layout) -> u64
 
@@ -1520,7 +1520,7 @@ pub fn vortex_layout::layouts::dict::Dict::metadata(&Self::Layout) -> Self::Meta
 
 pub fn vortex_layout::layouts::dict::Dict::nchildren(&Self::Layout) -> usize
 
-pub fn vortex_layout::layouts::dict::Dict::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
+pub fn vortex_layout::layouts::dict::Dict::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession, &vortex_layout::LayoutReaderContext) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
 
 pub fn vortex_layout::layouts::dict::Dict::row_count(&Self::Layout) -> u64
 
@@ -1552,7 +1552,7 @@ pub fn vortex_layout::layouts::flat::Flat::metadata(&Self::Layout) -> Self::Meta
 
 pub fn vortex_layout::layouts::flat::Flat::nchildren(&Self::Layout) -> usize
 
-pub fn vortex_layout::layouts::flat::Flat::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
+pub fn vortex_layout::layouts::flat::Flat::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession, &vortex_layout::LayoutReaderContext) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
 
 pub fn vortex_layout::layouts::flat::Flat::row_count(&Self::Layout) -> u64
 
@@ -1584,7 +1584,7 @@ pub fn vortex_layout::layouts::struct_::Struct::metadata(&Self::Layout) -> Self:
 
 pub fn vortex_layout::layouts::struct_::Struct::nchildren(&Self::Layout) -> usize
 
-pub fn vortex_layout::layouts::struct_::Struct::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
+pub fn vortex_layout::layouts::struct_::Struct::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession, &vortex_layout::LayoutReaderContext) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
 
 pub fn vortex_layout::layouts::struct_::Struct::row_count(&Self::Layout) -> u64
 
@@ -1616,7 +1616,7 @@ pub fn vortex_layout::layouts::zoned::Zoned::metadata(&Self::Layout) -> Self::Me
 
 pub fn vortex_layout::layouts::zoned::Zoned::nchildren(&Self::Layout) -> usize
 
-pub fn vortex_layout::layouts::zoned::Zoned::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
+pub fn vortex_layout::layouts::zoned::Zoned::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession, &vortex_layout::LayoutReaderContext) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
 
 pub fn vortex_layout::layouts::zoned::Zoned::row_count(&Self::Layout) -> u64
 
@@ -1682,7 +1682,7 @@ pub fn vortex_layout::LayoutAdapter<V>::metadata(&self) -> alloc::vec::Vec<u8>
 
 pub fn vortex_layout::LayoutAdapter<V>::nchildren(&self) -> usize
 
-pub fn vortex_layout::LayoutAdapter<V>::new_reader(&self, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
+pub fn vortex_layout::LayoutAdapter<V>::new_reader(&self, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession, &vortex_layout::LayoutReaderContext) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
 
 pub fn vortex_layout::LayoutAdapter<V>::row_count(&self) -> u64
 
@@ -1704,13 +1704,35 @@ pub fn vortex_layout::LayoutEncodingAdapter<V>::build(&self, &vortex_array::dtyp
 
 pub fn vortex_layout::LayoutEncodingAdapter<V>::id(&self) -> vortex_layout::LayoutEncodingId
 
+pub struct vortex_layout::LayoutReaderContext
+
+impl vortex_layout::LayoutReaderContext
+
+pub fn vortex_layout::LayoutReaderContext::get<T: core::any::Any + core::marker::Send + core::marker::Sync>(&self) -> core::option::Option<alloc::sync::Arc<T>>
+
+pub fn vortex_layout::LayoutReaderContext::new() -> Self
+
+pub fn vortex_layout::LayoutReaderContext::with<T: core::any::Any + core::marker::Send + core::marker::Sync>(&self, alloc::sync::Arc<T>) -> Self
+
+impl core::clone::Clone for vortex_layout::LayoutReaderContext
+
+pub fn vortex_layout::LayoutReaderContext::clone(&self) -> vortex_layout::LayoutReaderContext
+
+impl core::default::Default for vortex_layout::LayoutReaderContext
+
+pub fn vortex_layout::LayoutReaderContext::default() -> vortex_layout::LayoutReaderContext
+
+impl core::fmt::Debug for vortex_layout::LayoutReaderContext
+
+pub fn vortex_layout::LayoutReaderContext::fmt(&self, &mut core::fmt::Formatter<'_>) -> core::fmt::Result
+
 pub struct vortex_layout::LazyReaderChildren
 
 impl vortex_layout::LazyReaderChildren
 
 pub fn vortex_layout::LazyReaderChildren::get(&self, usize) -> vortex_error::VortexResult<&vortex_layout::LayoutReaderRef>
 
-pub fn vortex_layout::LazyReaderChildren::new(alloc::sync::Arc<dyn vortex_layout::LayoutChildren>, alloc::vec::Vec<vortex_array::dtype::DType>, alloc::vec::Vec<alloc::sync::Arc<str>>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, vortex_session::VortexSession) -> Self
+pub fn vortex_layout::LazyReaderChildren::new(alloc::sync::Arc<dyn vortex_layout::LayoutChildren>, alloc::vec::Vec<vortex_array::dtype::DType>, alloc::vec::Vec<alloc::sync::Arc<str>>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, vortex_session::VortexSession, vortex_layout::LayoutReaderContext) -> Self
 
 pub struct vortex_layout::SplitRange
 
@@ -1798,7 +1820,7 @@ pub fn vortex_layout::Layout::metadata(&self) -> alloc::vec::Vec<u8>
 
 pub fn vortex_layout::Layout::nchildren(&self) -> usize
 
-pub fn vortex_layout::Layout::new_reader(&self, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
+pub fn vortex_layout::Layout::new_reader(&self, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession, &vortex_layout::LayoutReaderContext) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
 
 pub fn vortex_layout::Layout::row_count(&self) -> u64
 
@@ -1824,7 +1846,7 @@ pub fn vortex_layout::LayoutAdapter<V>::metadata(&self) -> alloc::vec::Vec<u8>
 
 pub fn vortex_layout::LayoutAdapter<V>::nchildren(&self) -> usize
 
-pub fn vortex_layout::LayoutAdapter<V>::new_reader(&self, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
+pub fn vortex_layout::LayoutAdapter<V>::new_reader(&self, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession, &vortex_layout::LayoutReaderContext) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
 
 pub fn vortex_layout::LayoutAdapter<V>::row_count(&self) -> u64
 
@@ -1994,7 +2016,7 @@ pub fn vortex_layout::VTable::metadata(&Self::Layout) -> Self::Metadata
 
 pub fn vortex_layout::VTable::nchildren(&Self::Layout) -> usize
 
-pub fn vortex_layout::VTable::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
+pub fn vortex_layout::VTable::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession, &vortex_layout::LayoutReaderContext) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
 
 pub fn vortex_layout::VTable::row_count(&Self::Layout) -> u64
 
@@ -2026,7 +2048,7 @@ pub fn vortex_layout::layouts::chunked::Chunked::metadata(&Self::Layout) -> Self
 
 pub fn vortex_layout::layouts::chunked::Chunked::nchildren(&Self::Layout) -> usize
 
-pub fn vortex_layout::layouts::chunked::Chunked::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
+pub fn vortex_layout::layouts::chunked::Chunked::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession, &vortex_layout::LayoutReaderContext) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
 
 pub fn vortex_layout::layouts::chunked::Chunked::row_count(&Self::Layout) -> u64
 
@@ -2058,7 +2080,7 @@ pub fn vortex_layout::layouts::dict::Dict::metadata(&Self::Layout) -> Self::Meta
 
 pub fn vortex_layout::layouts::dict::Dict::nchildren(&Self::Layout) -> usize
 
-pub fn vortex_layout::layouts::dict::Dict::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
+pub fn vortex_layout::layouts::dict::Dict::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession, &vortex_layout::LayoutReaderContext) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
 
 pub fn vortex_layout::layouts::dict::Dict::row_count(&Self::Layout) -> u64
 
@@ -2090,7 +2112,7 @@ pub fn vortex_layout::layouts::flat::Flat::metadata(&Self::Layout) -> Self::Meta
 
 pub fn vortex_layout::layouts::flat::Flat::nchildren(&Self::Layout) -> usize
 
-pub fn vortex_layout::layouts::flat::Flat::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
+pub fn vortex_layout::layouts::flat::Flat::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession, &vortex_layout::LayoutReaderContext) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
 
 pub fn vortex_layout::layouts::flat::Flat::row_count(&Self::Layout) -> u64
 
@@ -2122,7 +2144,7 @@ pub fn vortex_layout::layouts::struct_::Struct::metadata(&Self::Layout) -> Self:
 
 pub fn vortex_layout::layouts::struct_::Struct::nchildren(&Self::Layout) -> usize
 
-pub fn vortex_layout::layouts::struct_::Struct::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
+pub fn vortex_layout::layouts::struct_::Struct::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession, &vortex_layout::LayoutReaderContext) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
 
 pub fn vortex_layout::layouts::struct_::Struct::row_count(&Self::Layout) -> u64
 
@@ -2154,7 +2176,7 @@ pub fn vortex_layout::layouts::zoned::Zoned::metadata(&Self::Layout) -> Self::Me
 
 pub fn vortex_layout::layouts::zoned::Zoned::nchildren(&Self::Layout) -> usize
 
-pub fn vortex_layout::layouts::zoned::Zoned::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
+pub fn vortex_layout::layouts::zoned::Zoned::new_reader(&Self::Layout, alloc::sync::Arc<str>, alloc::sync::Arc<dyn vortex_layout::segments::SegmentSource>, &vortex_session::VortexSession, &vortex_layout::LayoutReaderContext) -> vortex_error::VortexResult<vortex_layout::LayoutReaderRef>
 
 pub fn vortex_layout::layouts::zoned::Zoned::row_count(&Self::Layout) -> u64
 
diff --git a/vortex-layout/src/layout.rs b/vortex-layout/src/layout.rs
index 11f0afd629c..e4ad80e2d37 100644
--- a/vortex-layout/src/layout.rs
+++ b/vortex-layout/src/layout.rs
@@ -19,6 +19,7 @@ use vortex_session::registry::Id;
 
 use crate::LayoutEncodingId;
 use crate::LayoutEncodingRef;
+use crate::LayoutReaderContext;
 use crate::LayoutReaderRef;
 use crate::VTable;
 use crate::display::DisplayLayoutTree;
@@ -63,11 +64,19 @@ pub trait Layout: 'static + Send + Sync + Debug + private::Sealed {
     /// Get the segment IDs for this layout.
     fn segment_ids(&self) -> Vec<SegmentId>;
 
+    /// Construct a new reader for this layout, using the given dependency context.
+    ///
+    /// `ctx` is the typed-data registry threaded through reader construction (see
+    /// [`LayoutReaderContext`]). Top-level callers (file open, tests) typically pass
+    /// `&LayoutReaderContext::new()`; recursive callers inside layout implementations
+    /// must propagate the `ctx` they were handed so ancestor-published values reach
+    /// descendants.
     fn new_reader(
         &self,
         name: Arc<str>,
         segment_source: Arc<dyn SegmentSource>,
         session: &VortexSession,
+        ctx: &LayoutReaderContext,
     ) -> VortexResult<LayoutReaderRef>;
 }
 
@@ -311,8 +320,9 @@ impl<V: VTable> Layout for LayoutAdapter<V> {
         name: Arc<str>,
         segment_source: Arc<dyn SegmentSource>,
         session: &VortexSession,
+        ctx: &LayoutReaderContext,
     ) -> VortexResult<LayoutReaderRef> {
-        V::new_reader(&self.0, name, segment_source, session)
+        V::new_reader(&self.0, name, segment_source, session, ctx)
     }
 }
 
diff --git a/vortex-layout/src/layouts/chunked/mod.rs b/vortex-layout/src/layouts/chunked/mod.rs
index 82fcb650607..ed6dd3d75ba 100644
--- a/vortex-layout/src/layouts/chunked/mod.rs
+++ b/vortex-layout/src/layouts/chunked/mod.rs
@@ -74,12 +74,14 @@ impl VTable for Chunked {
         name: Arc<str>,
         segment_source: Arc<dyn SegmentSource>,
         session: &VortexSession,
+        ctx: &crate::LayoutReaderContext,
     ) -> VortexResult<LayoutReaderRef> {
         Ok(Arc::new(ChunkedReader::new(
             layout.clone(),
             name,
             segment_source,
             session,
+            ctx.clone(),
         )))
     }
 
diff --git a/vortex-layout/src/layouts/chunked/reader.rs b/vortex-layout/src/layouts/chunked/reader.rs
index 94ab3272cd7..a71a1429006 100644
--- a/vortex-layout/src/layouts/chunked/reader.rs
+++ b/vortex-layout/src/layouts/chunked/reader.rs
@@ -47,6 +47,7 @@ impl ChunkedReader {
         name: Arc<str>,
         segment_source: Arc<dyn SegmentSource>,
         session: &VortexSession,
+        ctx: crate::LayoutReaderContext,
     ) -> Self {
         let nchildren = layout.nchildren();
 
@@ -66,6 +67,7 @@ impl ChunkedReader {
             names,
             segment_source,
             session.clone(),
+            ctx,
         );
 
         Self {
@@ -435,7 +437,12 @@ mod test {
     ) {
         let layout = nested_chunked_layout();
         let reader = layout
-            .new_reader("".into(), Arc::new(TestSegments::default()), &SESSION)
+            .new_reader(
+                "".into(),
+                Arc::new(TestSegments::default()),
+                &SESSION,
+                &Default::default(),
+            )
             .unwrap();
 
         let splits = SplitBy::Layout
@@ -451,7 +458,7 @@ mod test {
     ) {
         block_on(|_h| async {
             let result = layout
-                .new_reader("".into(), segments, &SESSION)
+                .new_reader("".into(), segments, &SESSION, &Default::default())
                 .unwrap()
                 .projection_evaluation(
                     &(0..layout.row_count()),
diff --git a/vortex-layout/src/layouts/dict/mod.rs b/vortex-layout/src/layouts/dict/mod.rs
index 7928b447fa9..5fb4ea080b4 100644
--- a/vortex-layout/src/layouts/dict/mod.rs
+++ b/vortex-layout/src/layouts/dict/mod.rs
@@ -92,12 +92,14 @@ impl VTable for Dict {
         name: Arc<str>,
         segment_source: Arc<dyn SegmentSource>,
         session: &VortexSession,
+        ctx: &crate::LayoutReaderContext,
     ) -> VortexResult<LayoutReaderRef> {
         Ok(Arc::new(DictReader::try_new(
             layout.clone(),
             name,
             segment_source,
             session.clone(),
+            ctx.clone(),
         )?))
     }
 
diff --git a/vortex-layout/src/layouts/dict/reader.rs b/vortex-layout/src/layouts/dict/reader.rs
index 96f12d53ece..327d6d234ab 100644
--- a/vortex-layout/src/layouts/dict/reader.rs
+++ b/vortex-layout/src/layouts/dict/reader.rs
@@ -58,17 +58,21 @@ impl DictReader {
         name: Arc<str>,
         segment_source: Arc<dyn SegmentSource>,
         session: VortexSession,
+        ctx: crate::LayoutReaderContext,
     ) -> VortexResult<Self> {
         let values_len = usize::try_from(layout.values.row_count())?;
         let values = layout.values.new_reader(
             format!("{name}.values").into(),
             Arc::clone(&segment_source),
             &session,
+            &ctx,
+        )?;
+        let codes = layout.codes.new_reader(
+            format!("{name}.codes").into(),
+            segment_source,
+            &session,
+            &ctx,
         )?;
-        let codes =
-            layout
-                .codes
-                .new_reader(format!("{name}.codes").into(), segment_source, &session)?;
 
         Ok(Self {
             layout,
@@ -370,7 +374,7 @@ mod tests {
             );
             assert!(layout.encoding_id() == LayoutId::new("vortex.dict"));
             let actual = layout
-                .new_reader("".into(), segments, &session)
+                .new_reader("".into(), segments, &session, &Default::default())
                 .unwrap()
                 .projection_evaluation(
                     &(0..layout.row_count()),
@@ -454,7 +458,7 @@ mod tests {
                 )),
             );
             let mask = layout
-                .new_reader("".into(), segments, &session)
+                .new_reader("".into(), segments, &session, &Default::default())
                 .unwrap()
                 .filter_evaluation(&(0..3), &filter, MaskFuture::new_true(3))
                 .unwrap()
@@ -515,7 +519,7 @@ mod tests {
             let expression = is_not_null(root());
             assert_eq!(layout.encoding_id(), LayoutId::new("vortex.dict"));
             let actual = layout
-                .new_reader("".into(), segments, &session)
+                .new_reader("".into(), segments, &session, &Default::default())
                 .unwrap()
                 .projection_evaluation(
                     &(0..layout.row_count()),
diff --git a/vortex-layout/src/layouts/flat/mod.rs b/vortex-layout/src/layouts/flat/mod.rs
index b167e633170..a652f82fe61 100644
--- a/vortex-layout/src/layouts/flat/mod.rs
+++ b/vortex-layout/src/layouts/flat/mod.rs
@@ -87,6 +87,7 @@ impl VTable for Flat {
         name: Arc<str>,
         segment_source: Arc<dyn SegmentSource>,
         session: &VortexSession,
+        _ctx: &crate::LayoutReaderContext,
     ) -> VortexResult<LayoutReaderRef> {
         Ok(Arc::new(FlatReader::new(
             layout.clone(),
diff --git a/vortex-layout/src/layouts/flat/reader.rs b/vortex-layout/src/layouts/flat/reader.rs
index 8817fe5c678..81e86b2f721 100644
--- a/vortex-layout/src/layouts/flat/reader.rs
+++ b/vortex-layout/src/layouts/flat/reader.rs
@@ -276,7 +276,7 @@ mod test {
             );
 
             let result = layout
-                .new_reader("".into(), segments, &SESSION)?
+                .new_reader("".into(), segments, &SESSION, &Default::default())?
                 .projection_evaluation(
                     &(0..layout.row_count()),
                     &root(),
@@ -313,7 +313,7 @@ mod test {
 
             let expr = gt(root(), lit(3i32));
             let result = layout
-                .new_reader("".into(), segments, &SESSION)
+                .new_reader("".into(), segments, &SESSION, &Default::default())
                 .unwrap()
                 .projection_evaluation(
                     &(0..layout.row_count()),
@@ -350,7 +350,7 @@ mod test {
                 .unwrap();
 
             let result = layout
-                .new_reader("".into(), segments, &SESSION)
+                .new_reader("".into(), segments, &SESSION, &Default::default())
                 .unwrap()
                 .projection_evaluation(&(2..4), &root(), MaskFuture::new_true(2))
                 .unwrap()
diff --git a/vortex-layout/src/layouts/flat/writer.rs b/vortex-layout/src/layouts/flat/writer.rs
index da250414951..83b245d49f1 100644
--- a/vortex-layout/src/layouts/flat/writer.rs
+++ b/vortex-layout/src/layouts/flat/writer.rs
@@ -260,7 +260,7 @@ mod tests {
                 .unwrap();
 
             let result = layout
-                .new_reader("".into(), segments, &SESSION)
+                .new_reader("".into(), segments, &SESSION, &Default::default())
                 .unwrap()
                 .projection_evaluation(
                     &(0..layout.row_count()),
@@ -311,7 +311,7 @@ mod tests {
                 .unwrap();
 
             let result = layout
-                .new_reader("".into(), segments, &SESSION)
+                .new_reader("".into(), segments, &SESSION, &Default::default())
                 .unwrap()
                 .projection_evaluation(
                     &(0..layout.row_count()),
@@ -384,7 +384,7 @@ mod tests {
 
             // We should be able to read the array we just wrote.
             let result: ArrayRef = layout
-                .new_reader("".into(), segments, &SESSION)
+                .new_reader("".into(), segments, &SESSION, &Default::default())
                 .unwrap()
                 .projection_evaluation(
                     &(0..layout.row_count()),
diff --git a/vortex-layout/src/layouts/foreign/mod.rs b/vortex-layout/src/layouts/foreign/mod.rs
index 9abacc8b26e..6e0a351b41b 100644
--- a/vortex-layout/src/layouts/foreign/mod.rs
+++ b/vortex-layout/src/layouts/foreign/mod.rs
@@ -171,6 +171,7 @@ impl Layout for ForeignLayout {
         _name: Arc<str>,
         _segment_source: Arc<dyn SegmentSource>,
         _session: &VortexSession,
+        _ctx: &crate::LayoutReaderContext,
     ) -> VortexResult<LayoutReaderRef> {
         vortex_bail!(
             "Cannot read unknown layout encoding '{}'",
diff --git a/vortex-layout/src/layouts/row_idx/mod.rs b/vortex-layout/src/layouts/row_idx/mod.rs
index 18fc62b05cd..a88c8ac5d69 100644
--- a/vortex-layout/src/layouts/row_idx/mod.rs
+++ b/vortex-layout/src/layouts/row_idx/mod.rs
@@ -370,7 +370,9 @@ mod tests {
             let expr = eq(root(), lit(3i32));
             let result = RowIdxLayoutReader::new(
                 0,
-                layout.new_reader("".into(), segments, &SESSION).unwrap(),
+                layout
+                    .new_reader("".into(), segments, &SESSION, &Default::default())
+                    .unwrap(),
                 SESSION.clone(),
             )
             .projection_evaluation(
@@ -411,7 +413,9 @@ mod tests {
             let expr = gt(row_idx(), lit(3u64));
             let result = RowIdxLayoutReader::new(
                 0,
-                layout.new_reader("".into(), segments, &SESSION).unwrap(),
+                layout
+                    .new_reader("".into(), segments, &SESSION, &Default::default())
+                    .unwrap(),
                 SESSION.clone(),
             )
             .projection_evaluation(
@@ -456,7 +460,9 @@ mod tests {
 
             let result = RowIdxLayoutReader::new(
                 0,
-                layout.new_reader("".into(), segments, &SESSION).unwrap(),
+                layout
+                    .new_reader("".into(), segments, &SESSION, &Default::default())
+                    .unwrap(),
                 SESSION.clone(),
             )
             .projection_evaluation(
diff --git a/vortex-layout/src/layouts/struct_/mod.rs b/vortex-layout/src/layouts/struct_/mod.rs
index 29843f096d8..39ada8ccaec 100644
--- a/vortex-layout/src/layouts/struct_/mod.rs
+++ b/vortex-layout/src/layouts/struct_/mod.rs
@@ -114,12 +114,14 @@ impl VTable for Struct {
         name: Arc<str>,
         segment_source: Arc<dyn SegmentSource>,
         session: &VortexSession,
+        ctx: &crate::LayoutReaderContext,
     ) -> VortexResult<LayoutReaderRef> {
         Ok(Arc::new(StructReader::try_new(
             layout.clone(),
             name,
             segment_source,
             session.session(),
+            ctx.clone(),
         )?))
     }
 
diff --git a/vortex-layout/src/layouts/struct_/reader.rs b/vortex-layout/src/layouts/struct_/reader.rs
index 156c7456ed6..edac60ff6f4 100644
--- a/vortex-layout/src/layouts/struct_/reader.rs
+++ b/vortex-layout/src/layouts/struct_/reader.rs
@@ -68,6 +68,7 @@ impl StructReader {
         name: Arc<str>,
         segment_source: Arc<dyn SegmentSource>,
         session: VortexSession,
+        ctx: crate::LayoutReaderContext,
     ) -> VortexResult<Self> {
         let struct_dt = layout.struct_fields();
 
@@ -99,6 +100,7 @@ impl StructReader {
             names,
             Arc::clone(&segment_source),
             session.clone(),
+            ctx,
         );
 
         // Create an expanded root expression that contains all fields of the struct.
@@ -616,7 +618,9 @@ mod tests {
     fn test_struct_layout_or(
         #[from(struct_layout)] (segments, layout): (Arc<dyn SegmentSource>, LayoutRef),
     ) {
-        let reader = layout.new_reader("".into(), segments, &SESSION).unwrap();
+        let reader = layout
+            .new_reader("".into(), segments, &SESSION, &Default::default())
+            .unwrap();
         let filt = or(
             eq(col("a"), lit(7)),
             or(eq(col("b"), lit(5)), eq(col("a"), lit(3))),
@@ -634,7 +638,9 @@ mod tests {
     fn test_struct_layout(
         #[from(struct_layout)] (segments, layout): (Arc<dyn SegmentSource>, LayoutRef),
     ) {
-        let reader = layout.new_reader("".into(), segments, &SESSION).unwrap();
+        let reader = layout
+            .new_reader("".into(), segments, &SESSION, &Default::default())
+            .unwrap();
         let expr = gt(get_item("a", root()), get_item("b", root()));
         let result = block_on(|_| {
             reader
@@ -650,7 +656,9 @@ mod tests {
     fn test_struct_layout_row_mask(
         #[from(struct_layout)] (segments, layout): (Arc<dyn SegmentSource>, LayoutRef),
     ) {
-        let reader = layout.new_reader("".into(), segments, &SESSION).unwrap();
+        let reader = layout
+            .new_reader("".into(), segments, &SESSION, &Default::default())
+            .unwrap();
         let expr = gt(get_item("a", root()), get_item("b", root()));
         let result = block_on(|_| {
             reader
@@ -672,7 +680,9 @@ mod tests {
         #[from(struct_layout)] (segments, layout): (Arc<dyn SegmentSource>, LayoutRef),
     ) {
         let mut ctx = LEGACY_SESSION.create_execution_ctx();
-        let reader = layout.new_reader("".into(), segments, &SESSION).unwrap();
+        let reader = layout
+            .new_reader("".into(), segments, &SESSION, &Default::default())
+            .unwrap();
         let expr = pack(
             [("a", get_item("a", root())), ("b", get_item("b", root()))],
             Nullability::NonNullable,
@@ -711,7 +721,9 @@ mod tests {
         #[from(null_struct_layout)] (segments, layout): (Arc<dyn SegmentSource>, LayoutRef),
     ) {
         // Read the layout source from the top.
-        let reader = layout.new_reader("".into(), segments, &SESSION).unwrap();
+        let reader = layout
+            .new_reader("".into(), segments, &SESSION, &Default::default())
+            .unwrap();
         let expr = get_item("a", root());
         let project = reader
             .projection_evaluation(&(0..3), &expr, MaskFuture::new_true(3))
@@ -742,7 +754,9 @@ mod tests {
         // Project out the nested struct field.
         // The projection should preserve the nulls of the `b` struct when we select out the
         // child column `c`.
-        let reader = layout.new_reader("".into(), segments, &SESSION).unwrap();
+        let reader = layout
+            .new_reader("".into(), segments, &SESSION, &Default::default())
+            .unwrap();
         let expr = select(
             vec![FieldName::from("c")],
             get_item("b", get_item("a", root())),
@@ -803,7 +817,9 @@ mod tests {
     fn test_empty_struct(
         #[from(empty_struct)] (segments, layout): (Arc<dyn SegmentSource>, LayoutRef),
     ) {
-        let reader = layout.new_reader("".into(), segments, &SESSION).unwrap();
+        let reader = layout
+            .new_reader("".into(), segments, &SESSION, &Default::default())
+            .unwrap();
         let expr = pack(Vec::<(String, Expression)>::new(), Nullability::Nullable);
 
         let project = reader
@@ -854,7 +870,9 @@ mod tests {
         })
         .unwrap();
 
-        let reader = layout.new_reader("".into(), segments, &SESSION).unwrap();
+        let reader = layout
+            .new_reader("".into(), segments, &SESSION, &Default::default())
+            .unwrap();
 
         // DType mismatch: "age" is u8 but literal is i32
         let filt = eq(col("age"), lit(67i32));
diff --git a/vortex-layout/src/layouts/zoned/mod.rs b/vortex-layout/src/layouts/zoned/mod.rs
index 697e55e968c..43f9410e831 100644
--- a/vortex-layout/src/layouts/zoned/mod.rs
+++ b/vortex-layout/src/layouts/zoned/mod.rs
@@ -115,12 +115,14 @@ impl VTable for Zoned {
         name: Arc<str>,
         segment_source: Arc<dyn SegmentSource>,
         session: &VortexSession,
+        ctx: &crate::LayoutReaderContext,
     ) -> VortexResult<LayoutReaderRef> {
         Ok(Arc::new(ZonedReader::try_new(
             layout.clone(),
             name,
             segment_source,
             session.clone(),
+            ctx.clone(),
         )?))
     }
 
diff --git a/vortex-layout/src/layouts/zoned/reader.rs b/vortex-layout/src/layouts/zoned/reader.rs
index a73ed6a547c..6a544c7af1c 100644
--- a/vortex-layout/src/layouts/zoned/reader.rs
+++ b/vortex-layout/src/layouts/zoned/reader.rs
@@ -42,6 +42,7 @@ impl ZonedReader {
         name: Arc<str>,
         segment_source: Arc<dyn SegmentSource>,
         session: VortexSession,
+        ctx: crate::LayoutReaderContext,
     ) -> VortexResult<Self> {
         let dtypes = vec![
             layout.dtype.clone(),
@@ -54,6 +55,7 @@ impl ZonedReader {
             names,
             Arc::clone(&segment_source),
             session.clone(),
+            ctx,
         ));
 
         Ok(Self {
@@ -307,7 +309,7 @@ mod test {
         block_on(|handle| async {
             let session = session_with_handle(handle);
             let result = layout
-                .new_reader("".into(), segments, &session)
+                .new_reader("".into(), segments, &session, &Default::default())
                 .unwrap()
                 .projection_evaluation(
                     &(0..layout.row_count()),
@@ -330,7 +332,9 @@ mod test {
         block_on(|handle| async {
             let row_count = layout.row_count();
             let session = session_with_handle(handle);
-            let reader = layout.new_reader("".into(), segments, &session).unwrap();
+            let reader = layout
+                .new_reader("".into(), segments, &session, &Default::default())
+                .unwrap();
 
             // Choose a prune-able expression
             let expr = gt(root(), lit(7));
@@ -376,7 +380,8 @@ mod test {
         block_on(|handle| async {
             let row_count = legacy_layout.row_count();
             let session = session_with_handle(handle);
-            let reader = legacy_layout.new_reader("".into(), segments, &session)?;
+            let reader =
+                legacy_layout.new_reader("".into(), segments, &session, &Default::default())?;
 
             let result = reader
                 .pruning_evaluation(
diff --git a/vortex-layout/src/reader.rs b/vortex-layout/src/reader.rs
index b40339e3946..d22afd4a4f4 100644
--- a/vortex-layout/src/reader.rs
+++ b/vortex-layout/src/reader.rs
@@ -2,6 +2,7 @@
 // SPDX-FileCopyrightText: Copyright the Vortex contributors
 
 use std::any::Any;
+use std::any::TypeId;
 use std::collections::BTreeSet;
 use std::ops::Range;
 use std::sync::Arc;
@@ -20,6 +21,7 @@ use vortex_error::VortexResult;
 use vortex_error::vortex_bail;
 use vortex_mask::Mask;
 use vortex_session::VortexSession;
+use vortex_utils::aliases::hash_map::HashMap;
 
 use crate::children::LayoutChildren;
 use crate::segments::SegmentSource;
@@ -181,6 +183,7 @@ pub struct LazyReaderChildren {
     names: Vec<Arc<str>>,
     segment_source: Arc<dyn SegmentSource>,
     session: VortexSession,
+    ctx: LayoutReaderContext,
     // TODO(ngates): we may want a hash map of some sort here?
     cache: Vec<OnceCell<LayoutReaderRef>>,
 }
@@ -192,6 +195,7 @@ impl LazyReaderChildren {
         names: Vec<Arc<str>>,
         segment_source: Arc<dyn SegmentSource>,
         session: VortexSession,
+        ctx: LayoutReaderContext,
     ) -> Self {
         let nchildren = children.nchildren();
         let cache = (0..nchildren).map(|_| OnceCell::new()).collect();
@@ -201,6 +205,7 @@ impl LazyReaderChildren {
             names,
             segment_source,
             session,
+            ctx,
             cache,
         }
     }
@@ -217,7 +222,62 @@ impl LazyReaderChildren {
                 Arc::clone(&self.names[idx]),
                 Arc::clone(&self.segment_source),
                 &self.session,
+                &self.ctx,
             )
         })
     }
 }
+
+/// Per-reader-tree dependency context, threaded through [`crate::VTable::new_reader`].
+///
+/// Holds a typed-data registry keyed by [`TypeId`]. Ancestors publish values via
+/// [`Self::with`]; descendants retrieve them via [`Self::get`]. This is a *read-only*
+/// channel from the ancestor's perspective — descendants can only consume what their
+/// ancestors chose to publish,
+///
+/// [`Self::with`] returns a derived context that copies the existing map and adds (or
+/// replaces) one entry. The original is unchanged, allowing concurrent reader-tree
+/// constructions to each derive their own context without races. When the same `T` is
+/// published at multiple ancestors, the innermost (most-recently-published) wins.
+///
+/// Contexts are cheap to clone (shared via `Arc`), so they can be captured by lazy
+/// children helpers and survive any single stack frame.
+#[derive(Clone, Default)]
+pub struct LayoutReaderContext {
+    values: Arc<HashMap<TypeId, Arc<dyn Any + Send + Sync>>>,
+}
+
+impl std::fmt::Debug for LayoutReaderContext {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("LayoutReaderContext")
+            .field("type_ids", &self.values.keys().collect::<Vec<_>>())
+            .finish()
+    }
+}
+
+impl LayoutReaderContext {
+    /// Creates a new, empty context.
+    pub fn new() -> Self {
+        Self::default()
+    }
+
+    /// Returns a new context that publishes `value` under its concrete type.
+    ///
+    /// The original context is unchanged. If a value of the same type was already
+    /// published, the new one replaces it in the returned context.
+    pub fn with<T: Any + Send + Sync>(&self, value: Arc<T>) -> Self {
+        let mut values = HashMap::clone(&self.values);
+        values.insert(TypeId::of::<T>(), value);
+        Self {
+            values: Arc::new(values),
+        }
+    }
+
+    /// Returns the most-recently-published value of type `T`, or `None` if no ancestor
+    /// published one.
+    pub fn get<T: Any + Send + Sync>(&self) -> Option<Arc<T>> {
+        self.values
+            .get(&TypeId::of::<T>())
+            .and_then(|v| Arc::clone(v).downcast::<T>().ok())
+    }
+}
diff --git a/vortex-layout/src/scan/split_by.rs b/vortex-layout/src/scan/split_by.rs
index 8cc6e2e095a..d17957a739b 100644
--- a/vortex-layout/src/scan/split_by.rs
+++ b/vortex-layout/src/scan/split_by.rs
@@ -98,7 +98,7 @@ mod test {
         .unwrap();
 
         layout
-            .new_reader("".into(), segments, &SCAN_SESSION)
+            .new_reader("".into(), segments, &SCAN_SESSION, &Default::default())
             .unwrap()
     }
 
diff --git a/vortex-layout/src/vtable.rs b/vortex-layout/src/vtable.rs
index 9bb83fcf643..c48a9d33d1f 100644
--- a/vortex-layout/src/vtable.rs
+++ b/vortex-layout/src/vtable.rs
@@ -19,6 +19,7 @@ use crate::LayoutChildType;
 use crate::LayoutEncoding;
 use crate::LayoutEncodingRef;
 use crate::LayoutId;
+use crate::LayoutReaderContext;
 use crate::LayoutReaderRef;
 use crate::LayoutRef;
 use crate::children::LayoutChildren;
@@ -58,11 +59,20 @@ pub trait VTable: 'static + Sized + Send + Sync + Debug {
     fn child_type(layout: &Self::Layout, idx: usize) -> LayoutChildType;
 
     /// Create a new reader for the layout.
+    ///
+    /// **Layouts with children MUST propagate `ctx` to descendants** by passing it
+    /// through `Layout::new_reader` (or `LazyReaderChildren::new`) when constructing
+    /// child readers. If `ctx` is dropped at any link in the chain, ancestor-published
+    /// values won't reach affected descendants — a silent runtime regression for any
+    /// descendant that looked up an ancestor-published value via `ctx.get::<T>()`.
+    /// There is no compile-time check that catches this; reviewer discipline + the
+    /// integration tests in `vortex-layout` are the only safety net.
     fn new_reader(
         layout: &Self::Layout,
         name: Arc<str>,
         segment_source: Arc<dyn SegmentSource>,
         session: &VortexSession,
+        ctx: &LayoutReaderContext,
     ) -> VortexResult<LayoutReaderRef>;
 
     /// Construct a new [`Layout`] from the provided parts.
diff --git a/vortex-test/compat-gen/src/adapter.rs b/vortex-test/compat-gen/src/adapter.rs
index a97399dac79..bed1300b531 100644
--- a/vortex-test/compat-gen/src/adapter.rs
+++ b/vortex-test/compat-gen/src/adapter.rs
@@ -136,7 +136,12 @@ pub fn read_layout_tree(bytes: ByteBuffer) -> VortexResult<()> {
             if row_count == 0 {
                 continue;
             }
-            let reader = layout.new_reader("".into(), Arc::clone(&segment_source), &session)?;
+            let reader = layout.new_reader(
+                "".into(),
+                Arc::clone(&segment_source),
+                &session,
+                &Default::default(),
+            )?;
             let len =
                 usize::try_from(row_count).map_err(|e| vortex_err!("row count overflow: {e}"))?;
             reader
diff --git a/vortex-tui/src/browse/app.rs b/vortex-tui/src/browse/app.rs
index 0a7f13ab277..97e17bac205 100644
--- a/vortex-tui/src/browse/app.rs
+++ b/vortex-tui/src/browse/app.rs
@@ -360,7 +360,12 @@ impl AppState {
 
         // Load the array.
         let reader = layout
-            .new_reader("".into(), self.vxf.segment_source(), &self.session)
+            .new_reader(
+                "".into(),
+                self.vxf.segment_source(),
+                &self.session,
+                &Default::default(),
+            )
             .vortex_expect("Failed to create reader");
         let array = reader
             .projection_evaluation(
diff --git a/vortex-tui/src/wasm.rs b/vortex-tui/src/wasm.rs
index 8b643161fe2..5fd7dd9054b 100644
--- a/vortex-tui/src/wasm.rs
+++ b/vortex-tui/src/wasm.rs
@@ -78,7 +78,12 @@ async fn load_flat_array(
     row_count: u64,
 ) -> vortex::array::ArrayRef {
     let reader = layout
-        .new_reader("".into(), segment_source.clone(), session)
+        .new_reader(
+            "".into(),
+            segment_source.clone(),
+            session,
+            &Default::default(),
+        )
         .vortex_expect("Failed to create reader");
     reader
         .projection_evaluation(
diff --git a/vortex-web/crate/src/wasm.rs b/vortex-web/crate/src/wasm.rs
index 05e328e5341..f1bb4df791e 100644
--- a/vortex-web/crate/src/wasm.rs
+++ b/vortex-web/crate/src/wasm.rs
@@ -293,7 +293,12 @@ impl VortexFileHandle {
 
         let segment_source = self.vxf.segment_source();
         let reader = layout
-            .new_reader(node_id.into(), segment_source, &self.session)
+            .new_reader(
+                node_id.into(),
+                segment_source,
+                &self.session,
+                &Default::default(),
+            )
             .map_err(|e| JsValue::from_str(&e.to_string()))?;
 
         let stream = ScanBuilder::new(self.session.clone(), reader)