ocs_doc_api: Phase 2b-c (linear Dimension) — Phase 2 complete

- CreateDimensionLinear(DimensionSpec) op + GetDimensionMeasurement query (append-only).
- backend add_dimension_linear (Dimension::Linear via DimensionLinear::new) +
  dimension_measurement (linear/radius/diameter distance).
- Dimension bounds from measured + definition points; Dimension handle + measurement().
- spec Dimension family; api_reference + binding_schema regenerated; mocks + baseline.
- Test phase2c_dimension_linear_create_measurement_bounds -> 607 host lib + 8 crate
  + 3 consistency green. Phase 2 (full 2D + annotations) is now complete.

crates/ocs_doc_api/src/backend.rs

@@ -60,6 +60,12 @@ pub trait DocApiBackend {
     /// A hatch's boundary loops (outer + islands) as closed polylines.
     fn hatch_boundary(&self, id: ObjectId) -> ApiResult<Vec<Vec<[f64; 2]>>>;
 
+    /// Add a linear `DIMENSION`; returns the fresh `ObjectId`.
+    fn add_dimension_linear(&mut self, spec: &crate::ops::DimensionSpec) -> ApiResult<ObjectId>;
+
+    /// A dimension's measured value (distance for linear/radius, degrees for angular).
+    fn dimension_measurement(&self, id: ObjectId) -> ApiResult<f64>;
+
     /// Can `id` be modified in place right now (exists, is the expected family,
     /// not on a locked layer)? Read-only pre-check used before mutations.
     /// Default: existence + not-locked (backends narrow the family check).

crates/ocs_doc_api/src/executor.rs

@@ -221,6 +221,12 @@ pub fn apply_op<B: DocApiBackend>(b: &mut B, op: Operation) -> ApiResult<Receipt
             b.finalize_op();
             OpOutcome::NewId(id)
         }
+        Operation::CreateDimensionLinear(spec) => {
+            b.push_undo(name);
+            let id = b.add_dimension_linear(spec)?;
+            b.finalize_op();
+            OpOutcome::NewId(id)
+        }
     };
     Ok(Receipt {
         outcome: Some(outcome),
@@ -260,6 +266,7 @@ pub fn apply_queries<B: DocApiBackend>(b: &mut B, queries: Vec<Query>) -> ApiRes
             Query::GetGeometryRevision => QueryResult::Revision(b.revision()),
             Query::GetTextContent { id } => QueryResult::TextContent(b.text_content(id)?),
             Query::GetHatchBoundary { id } => QueryResult::HatchBoundary(b.hatch_boundary(id)?),
+            Query::GetDimensionMeasurement { id } => QueryResult::DimensionMeasurement(b.dimension_measurement(id)?),
         };
         results.push(r);
     }

crates/ocs_doc_api/src/facade.rs

@@ -269,6 +269,18 @@ handle!(Ray);
 handle!(XLine);
 handle!(Text);
 handle!(MText);
+handle!(Dimension);
+
+impl Dimension {
+    /// The measured value of this dimension (distance for linear/radius, degrees
+    /// for angular).
+    pub fn measurement(&self) -> ApiResult<f64> {
+        match self.session.one_query(Query::GetDimensionMeasurement { id: self.id })? {
+            QueryResult::DimensionMeasurement(v) => Ok(v),
+            _ => Err(ApiError::Transport("unexpected measurement result".into())),
+        }
+    }
+}
 
 impl Entity {
     pub fn view(&self) -> ApiResult<EntityView> {
@@ -475,6 +487,16 @@ impl CurveCollection {
         Ok(Entity::new(self.session.clone(), id))
     }
 
+    /// A linear DIMENSION between `first_point` and `second_point`, with the
+    /// dimension line placed at `definition_point`. `measurement()` reads the value.
+    pub fn create_dimension_linear(&self, first_point: [f64; 3], second_point: [f64; 3], definition_point: [f64; 3]) -> ApiResult<Dimension> {
+        let receipt = self.session.apply_op(Operation::CreateDimensionLinear(crate::ops::DimensionSpec {
+            first_point, second_point, definition_point,
+        }))?;
+        let id = receipt.outcome.and_then(|o| o.new_id()).ok_or_else(|| ApiError::Transport("create_dimension returned no id".into()))?;
+        Ok(Dimension::new(self.session.clone(), id))
+    }
+
     /// Single-line TEXT annotation.
     pub fn create_text(&self, value: &str, insertion_point: [f64; 3], height: f64, rotation: f64) -> ApiResult<Text> {
         let receipt = self.session.apply_op(Operation::CreateText(crate::ops::TextSpec {

crates/ocs_doc_api/src/gen/api_reference.md

@@ -125,6 +125,18 @@ Filled region over a closed polyline boundary. boundary() returns the loops; bou
 
 - **boundary**(``) -> `Vec<Vec<[f64; 2]>>` — query `GetHatchBoundary`
 
+## `Dimension` (acadrust `Dimension`, collection `curves`)
+
+Linear dimension between two measured points. measurement() reads the distance; bounds from the measured + definition points.
+
+### Constructors (`doc.curves()`)
+
+- **create_dimension_linear**(`first_point: [f64; 3], second_point: [f64; 3], definition_point: [f64; 3]`) -> `Dimension`
+
+### Methods
+
+- **measurement**(``) -> `f64` — query `GetDimensionMeasurement`
+
 ## `Entity` (acadrust `Insert`, collection `entities`)
 
 Block reference. Place an existing BlockRecord by name; transform moves its insert point.

crates/ocs_doc_api/src/gen/binding_schema.json

@@ -277,6 +277,25 @@
       ],
       "name": "Hatch"
     },
+    {
+      "acadrust_variant": "Dimension",
+      "collection": "curves",
+      "handle": "Dimension",
+      "methods": [
+        {
+          "args": [],
+          "bulk": false,
+          "fixed": null,
+          "kind": "query",
+          "name": "measurement",
+          "op": null,
+          "query": "GetDimensionMeasurement",
+          "read_only": true,
+          "returns": "f64"
+        }
+      ],
+      "name": "Dimension"
+    },
     {
       "acadrust_variant": "Insert",
       "collection": "entities",
@@ -361,7 +380,8 @@
       "Ray",
       "XLine",
       "Text",
-      "MText"
+      "MText",
+      "Dimension"
     ],
     "root": "DocApi"
   },

crates/ocs_doc_api/src/gen/ops_gen.rs

@@ -7,7 +7,7 @@
 use serde::{Deserialize, Serialize};
 
 use crate::id::ObjectId;
-use crate::ops::{BoolOp, Curve2Spec, EntitySpec, HatchSpec, InsertSpec, MTextSpec, PlacementSpec, SolidPrimitive, TextSpec, ViewportSpec};
+use crate::ops::{BoolOp, Curve2Spec, DimensionSpec, EntitySpec, HatchSpec, InsertSpec, MTextSpec, PlacementSpec, SolidPrimitive, TextSpec, ViewportSpec};
 
 /// A typed write operation (plan §5). Each variant is ONE atomic host call = one
 /// undo step. Append new variants at the END only.
@@ -38,4 +38,6 @@ pub enum Operation {
     SetTextContent { id: ObjectId, value: String },
     // hatch
     CreateHatch(HatchSpec),
+    // dimensions
+    CreateDimensionLinear(DimensionSpec),
 }

crates/ocs_doc_api/src/gen/query_gen.rs

@@ -23,4 +23,6 @@ pub enum Query {
     GetTextContent { id: ObjectId },
     /// The boundary loops of a Hatch (outer + islands) as polylines.
     GetHatchBoundary { id: ObjectId },
+    /// The measured value of a Dimension (distance or angle).
+    GetDimensionMeasurement { id: ObjectId },
 }

crates/ocs_doc_api/src/ops.rs

@@ -106,6 +106,15 @@ pub struct HatchSpec {
     pub solid: bool,
 }
 
+/// Construction spec for a linear `DIMENSION`: the two measured points and the
+/// dimension-line definition point.
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub struct DimensionSpec {
+    pub first_point: [f64; 3],
+    pub second_point: [f64; 3],
+    pub definition_point: [f64; 3],
+}
+
 /// A rigid similarity (rotation + translation + optional uniform scale/reflection)
 /// as a plain-data mirror of `cadkernel::brep::transform`'s `Placement`
 /// (non-serde). Columns are the new basis axes; `origin` is the translation.
@@ -159,6 +168,7 @@ impl crate::gen::Operation {
             CreateMText(_) => "CreateMText",
             SetTextContent { .. } => "SetTextContent",
             CreateHatch(_) => "CreateHatch",
+            CreateDimensionLinear(_) => "CreateDimensionLinear",
         }
     }
 }

crates/ocs_doc_api/src/query.rs

@@ -47,6 +47,8 @@ pub enum QueryResult {
     TextContent(String),
     /// A hatch's boundary loops (outer + islands), each a closed polyline.
     HatchBoundary(Vec<Vec<[f64; 2]>>),
+    /// A dimension's measured value (distance for linear/radius, degrees for angular).
+    DimensionMeasurement(f64),
 }
 
 /// Convenience: the query name for diagnostics.
@@ -62,6 +64,7 @@ impl crate::gen::Query {
             GetGeometryRevision => "GetGeometryRevision",
             GetTextContent { .. } => "GetTextContent",
             GetHatchBoundary { .. } => "GetHatchBoundary",
+            GetDimensionMeasurement { .. } => "GetDimensionMeasurement",
         }
     }
 }