ocs_doc_api: Phase 3 attributes + nested block traversal

- SetAttribute op + GetAttributes/GetBlockEntities queries (append-only).
- backend set_attribute (add/update Insert attribute), attributes (tag,value pairs),
  block_entities (read-only traversal via BlockRecord.entity_handles -> id+kind+bounds).
- facade Entity::set_attribute/attributes, Document::block_entities.
- spec Insert methods; api_reference + binding_schema regenerated; mocks + baseline.
- Query enum: drop Copy (GetBlockEntities carries String).
- Test phase3_attributes_and_block_traversal -> 608 host lib + 3 consistency green.

crates/ocs_doc_api/tests/mock_backend.rs

@@ -27,6 +27,8 @@ struct MockBackend {
     hatch_boundaries: HashMap<ObjectId, Vec<Vec<[f64; 2]>>>,
     /// Stored dimension measurements.
     dimension_measurements: HashMap<ObjectId, f64>,
+    /// Stored insert attributes.
+    attributes_store: HashMap<ObjectId, Vec<(String, String)>>,
 }
 
 impl MockBackend {
@@ -120,6 +122,25 @@ impl DocApiBackend for MockBackend {
     fn dimension_measurement(&self, id: ObjectId) -> ApiResult<f64> {
         self.dimension_measurements.get(&id).copied().ok_or(ApiError::UnknownId(id))
     }
+    fn set_attribute(&mut self, id: ObjectId, tag: &str, value: &str) -> ApiResult<()> {
+        if !self.entity_exists(id) {
+            return Err(ApiError::UnknownId(id));
+        }
+        let attrs = self.attributes_store.entry(id).or_default();
+        if let Some(a) = attrs.iter_mut().find(|(t, _)| t == tag) {
+            a.1 = value.to_string();
+        } else {
+            attrs.push((tag.to_string(), value.to_string()));
+        }
+        Ok(())
+    }
+    fn attributes(&self, id: ObjectId) -> ApiResult<Vec<(String, String)>> {
+        self.attributes_store.get(&id).cloned().ok_or(ApiError::UnknownId(id))
+    }
+    fn block_entities(&self, _block_name: &str) -> ApiResult<Vec<EntityView>> {
+        Ok(Vec::new())
+    }
+}
     fn add_vertex(&mut self, id: ObjectId, _at: usize, _point: [f64; 3]) -> ApiResult<()> {
         if self.entity_exists(id) {
             Ok(())

crates/ocs_doc_api/tests/spec_wire_consistency.rs

@@ -58,6 +58,7 @@ fn operation_variants() -> Vec<String> {
         Operation::SetTextContent { id: ObjectId::from_u64(0), value: String::new() },
         Operation::CreateHatch(ocs_doc_api::ops::HatchSpec { boundary: vec![], solid: true }),
         Operation::CreateDimensionLinear(ocs_doc_api::ops::DimensionSpec { first_point: [0.0; 3], second_point: [0.0; 3], definition_point: [0.0; 3] }),
+        Operation::SetAttribute { id: ObjectId::from_u64(0), tag: String::new(), value: String::new() },
     ];
     // Derive the variant names by serializing a probe of each and reading the
     // bincode variant index -> name map is not available; instead match by
@@ -85,6 +86,8 @@ fn query_variants() -> Vec<String> {
         Query::GetTextContent { id: ObjectId::from_u64(0) },
         Query::GetHatchBoundary { id: ObjectId::from_u64(0) },
         Query::GetDimensionMeasurement { id: ObjectId::from_u64(0) },
+        Query::GetAttributes { id: ObjectId::from_u64(0) },
+        Query::GetBlockEntities { block_name: String::new() },
     ];
     marker
         .iter()
@@ -140,6 +143,7 @@ const OPERATION_BASELINE: &[&str] = &[
     "SetTextContent",
     "CreateHatch",
     "CreateDimensionLinear",
+    "SetAttribute",
 ];
 
 /// Recorded baseline of the `Query` variant order.
@@ -153,6 +157,8 @@ const QUERY_BASELINE: &[&str] = &[
     "GetTextContent",
     "GetHatchBoundary",
     "GetDimensionMeasurement",
+    "GetAttributes",
+    "GetBlockEntities",
 ];
 
 #[test]