feat(shell): wire Document.var_table + canonical loader populates from PenDocument

Closes the gap between `VariableTable` (commits `62b08b93` /
`dbfd2f1a`) and the canonical `.op` loader: opening a file now
preserves `.variables` + `.themes` straight onto
`Document.var_table` instead of dropping them at the door.

  - `Document.var_table: VariableTable` field — Default = empty
    table. Patched 9 test fixtures (`tests_geometry.rs` × 7 +
    `canvas_viewport.rs` + `layer_panel_tests.rs`) to seed with
    `VariableTable::default()` alongside `history`.
  - `pen_doc_adapter::build_var_table(&PenDocument) -> VariableTable`
    maps `jian_ops_schema::variable::*` → shell-core types: the
    enums are isomorphic (Color/Number/Boolean/String;
    Bool/Num/Str; Scalar/Themed). Theme axes copy through directly.
  - `persistence.rs` open path: when the canonical branch fires,
    `build_var_table` runs alongside `pen_document_to_payload`. The
    result is held in a local `Option<VariableTable>` because
    `apply_payload` doesn't know about variables; after it resets
    the document, the held value is assigned to `doc.var_table`.

Round-trip: load → `doc.var_table.find("color-1")` returns the
right `Variable`, `doc.var_table.resolve("color-1")` returns the
themed value under the current `active_theme` (empty default —
picks the `theme = None` entry, mirroring `Variable::resolve`'s
fallback). UI for switching `active_theme` (Variables panel) +
paint-time `$ref` substitution are the remaining follow-ups for #5.

Tests: 184 shell-core + 19 shell-native (no new assertions in this
commit; variables algorithm tests landed in `dbfd2f1a`). Desktop
builds clean.

crates/openpencil-desktop/src/pen_doc_adapter.rs

@@ -81,6 +81,68 @@ pub fn pen_document_to_payload(doc: &PenDocument) -> LoadedDoc {
     }
 }
 
+/// Copy `PenDocument.variables` + `.themes` into a shell-core
+/// `VariableTable`. Caller assigns the result to `Document.var_table`
+/// AFTER `apply_payload` (which clears it via Default). Lossless on
+/// the supported `VariableDefinition` variants; unknown future
+/// `VariableKind`s round-trip via their `Color/Number/Boolean/String`
+/// label since the enums are isomorphic.
+pub fn build_var_table(doc: &PenDocument) -> openpencil_shell_core::document::VariableTable {
+    use openpencil_shell_core::document::{
+        ThemeAxis, ThemedValue, Variable, VariableKind, VariableScalar, VariableTable,
+        VariableValue,
+    };
+    let mut out = VariableTable::default();
+    if let Some(themes) = &doc.themes {
+        for (axis_name, values) in themes {
+            out.themes.push(ThemeAxis {
+                name: axis_name.clone(),
+                values: values.clone(),
+            });
+        }
+    }
+    if let Some(vars) = &doc.variables {
+        for (name, def) in vars {
+            let kind = match def.kind {
+                jian_ops_schema::variable::VariableKind::Color => VariableKind::Color,
+                jian_ops_schema::variable::VariableKind::Number => VariableKind::Number,
+                jian_ops_schema::variable::VariableKind::Boolean => VariableKind::Boolean,
+                jian_ops_schema::variable::VariableKind::String => VariableKind::String,
+            };
+            let value = match &def.value {
+                jian_ops_schema::variable::VariableValue::Scalar(s) => {
+                    VariableValue::Scalar(map_scalar(s))
+                }
+                jian_ops_schema::variable::VariableValue::Themed(arr) => VariableValue::Themed(
+                    arr.iter()
+                        .map(|tv| ThemedValue {
+                            value: map_scalar(&tv.value),
+                            theme: tv.theme.clone(),
+                        })
+                        .collect(),
+                ),
+            };
+            out.variables.push(Variable {
+                name: name.clone(),
+                kind,
+                value,
+            });
+        }
+    }
+    out
+}
+
+fn map_scalar(
+    s: &jian_ops_schema::variable::VariableScalar,
+) -> openpencil_shell_core::document::VariableScalar {
+    use openpencil_shell_core::document::VariableScalar;
+    match s {
+        jian_ops_schema::variable::VariableScalar::Bool(b) => VariableScalar::Bool(*b),
+        jian_ops_schema::variable::VariableScalar::Num(n) => VariableScalar::Num(*n),
+        jian_ops_schema::variable::VariableScalar::Str(s) => VariableScalar::Str(s.clone()),
+    }
+}
+
 fn build_page(id: &str, name: &str, roots: &[PenNode], page_idx: usize) -> PagePayload {
     let mut layout_rects: BTreeMap<String, [f32; 4]> = BTreeMap::new();
     for root in roots {

crates/openpencil-desktop/src/persistence.rs

@@ -392,7 +392,11 @@ fn load_from_path(doc: &mut Document, path: &std::path::Path) -> Result<(), Stri
     // its own Save), then fall back to the canonical `.op` /
     // `.pen` schema so files from the TS editor, Jian apps, or
     // anything else emitting the format load through the shared
-    // parser instead of a private adapter.
+    // parser instead of a private adapter. Side-channel: when the
+    // canonical path fires, also harvest `variables` + `themes` into
+    // a VariableTable for assignment after apply_payload (which
+    // resets Document state via Default).
+    let mut canonical_var_table: Option<openpencil_shell_core::document::VariableTable> = None;
     let payload = match serde_json::from_slice::<DocPayload>(&bytes) {
         Ok(p) => p,
         Err(_) => {
@@ -402,9 +406,7 @@ fn load_from_path(doc: &mut Document, path: &std::path::Path) -> Result<(), Stri
             for w in &loaded.warnings {
                 eprintln!("[open] schema warning: {:?}", w);
             }
-            // jian-core's `LayoutEngine` runs inside the adapter,
-            // so the returned payload already carries absolute
-            // scene-coord rects on every node.
+            canonical_var_table = Some(crate::pen_doc_adapter::build_var_table(&loaded.value));
             let adapted = crate::pen_doc_adapter::pen_document_to_payload(&loaded.value);
             adapted.payload
         }
@@ -412,6 +414,9 @@ fn load_from_path(doc: &mut Document, path: &std::path::Path) -> Result<(), Stri
     let page_count = payload.pages.len();
     let node_count: usize = payload.pages.iter().map(|p| count_nodes(&p.children)).sum();
     apply_payload(doc, payload)?;
+    if let Some(tbl) = canonical_var_table {
+        doc.var_table = tbl;
+    }
     let bb = active_page_bbox(doc);
     eprintln!(
         "[open] {} pages, {} nodes; content bbox {:?}; viewport pan=({:.1},{:.1}) zoom={:.2}",

crates/openpencil-shell-core/src/document.rs

@@ -272,6 +272,9 @@ pub struct Document {
     pub ui: UiState,
     /// Undo / redo stacks. Push BEFORE a transactional mutation.
     pub history: History,
+    /// Design variables + theme registry. Populated by the canonical
+    /// `.op` loader; lookup via `Variable::resolve` / `VariableTable::resolve`.
+    pub var_table: VariableTable,
 }
 
 /// Document undo / redo stacks. Snapshot = deep copy of the

crates/openpencil-shell-core/src/document/mutators.rs

@@ -48,6 +48,7 @@ impl Document {
             chat: ChatState::default(),
             ui: UiState::default(),
             history: History::default(),
+            var_table: VariableTable::default(),
         }
     }
 
@@ -95,6 +96,7 @@ impl Document {
             chat: ChatState::default(),
             ui: UiState::default(),
             history: History::default(),
+            var_table: VariableTable::default(),
         };
         debug_assert!(
             doc.validate().is_ok(),

crates/openpencil-shell-core/src/document/tests_geometry.rs

@@ -472,6 +472,7 @@ fn document_validate_catches_duplicate_node_id() {
         chat: ChatState::default(),
         ui: UiState::default(),
         history: crate::document::History::default(),
+            var_table: crate::document::VariableTable::default(),
     };
     let result = doc.validate();
     assert!(result.is_err());
@@ -506,6 +507,7 @@ fn document_validate_catches_empty_pages() {
         chat: ChatState::default(),
         ui: UiState::default(),
         history: crate::document::History::default(),
+            var_table: crate::document::VariableTable::default(),
     };
     let result = doc.validate();
     assert!(result.is_err());
@@ -530,6 +532,7 @@ fn document_validate_catches_empty_pages() {
         chat: ChatState::default(),
         ui: UiState::default(),
         history: crate::document::History::default(),
+            var_table: crate::document::VariableTable::default(),
     };
     let err2 = doc2.validate().unwrap_err();
     assert!(
@@ -559,6 +562,7 @@ fn document_selected_node_scopes_to_active_page() {
         chat: ChatState::default(),
         ui: UiState::default(),
         history: crate::document::History::default(),
+            var_table: crate::document::VariableTable::default(),
     };
     // Selection is on a non-active page → returns None.
     assert!(doc.selected_node().is_none());
@@ -588,6 +592,7 @@ fn document_active_page_returns_indexed_page() {
         chat: ChatState::default(),
         ui: UiState::default(),
         history: crate::document::History::default(),
+            var_table: crate::document::VariableTable::default(),
     };
     assert_eq!(doc.active_page().unwrap().name, "second");
 }
@@ -605,6 +610,7 @@ fn document_active_page_returns_none_when_index_out_of_range() {
         chat: ChatState::default(),
         ui: UiState::default(),
         history: crate::document::History::default(),
+            var_table: crate::document::VariableTable::default(),
     };
     assert!(doc.active_page().is_none());
 }
@@ -657,6 +663,7 @@ fn add_page_returns_none_on_id_overflow() {
         chat: ChatState::default(),
         ui: UiState::default(),
         history: crate::document::History::default(),
+            var_table: crate::document::VariableTable::default(),
     };
     let mut doc = doc;
     assert_eq!(doc.add_page(), None);

crates/openpencil-shell-core/src/widgets/canvas_viewport.rs

@@ -810,6 +810,7 @@ mod tests {
             chat: crate::document::ChatState::default(),
             ui: crate::document::UiState::default(),
             history: crate::document::History::default(),
+            var_table: crate::document::VariableTable::default(),
         };
         let viewport = CanvasViewport::from_document(&doc);
         let mut backend = RecordingBackend::default();

crates/openpencil-shell-core/src/widgets/layer_panel_tests.rs

@@ -135,6 +135,7 @@ fn from_document_scopes_to_active_page_only() {
         chat: crate::document::ChatState::default(),
         ui: crate::document::UiState::default(),
         history: crate::document::History::default(),
+            var_table: crate::document::VariableTable::default(),
     };
     let panel = LayerPanel::from_document(&doc);
     assert_eq!(panel.items.len(), 1);