Add ocs_doc_api: object-oriented CAD entity API (v2)

New crate crates/ocs_doc_api: object-centric facade (DocApi -> Document ->
collections -> typed handles), transport-agnostic wire layer (DocApiEnvelope =
single op | read-only query batch), per-op autocommit (no write transactions),
bulk ops with upfront-validation all-or-nothing, structured ApiError, and
build-time codegen (spec/entities.toml -> ops/query enums, api_reference.md,
binding_schema.json).

ocs_plugin_api: append-only PluginRequest::DocApiRequest / PluginResponse::
DocApiResponse (serde_bytes payload) + defaulted HostApi::doc_api_dispatch.

Host: DocApiBackend impl for HostSession (src/app/doc_api.rs) mapping to scene
primitives (solid_models lift-on-miss, register_prepared_solid_model, meshes
metrics), entity conversions (doc_api_convert.rs), HostSession accessors +
doc_api_dispatch override.

Tests: 592 host lib (incl. 7 DocApi integration tests: create/boolean/query,
unknown-id, transform-many all-or-nothing, query-batch cap, 2D/geometric/DWG
roundtrips), 8 crate unit tests. Examples + README/ARCHITECTURE/IMPLEMENTATION docs.

crates/ocs_doc_api/src/ops.rs

@@ -0,0 +1,97 @@
+//! Write operations — the typed, transport-agnostic vocabulary for changing the
+//! document (plan §5). The `Operation` enum itself is GENERATED into
+//! `crate::gen` by `build.rs` from `spec/entities.toml`; this module re-exports
+//! it and holds the hand-written payload mirrors.
+
+use serde::{Deserialize, Serialize};
+
+pub use crate::gen::Operation;
+
+/// Boolean operation kind for [`Operation::SolidBoolean`].
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+pub enum BoolOp {
+    Union,
+    Intersection,
+    Difference,
+}
+
+/// Construction spec for a B-rep solid primitive (plain-data mirror of the
+/// non-serde `cadkernel::brep::make::*` arguments).
+#[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
+pub enum SolidPrimitive {
+    Cuboid { origin: [f64; 3], size: [f64; 3] },
+    Sphere { centre: [f64; 3], radius: f64 },
+    Cylinder { base: [f64; 3], radius: f64, height: f64 },
+    Cone { base: [f64; 3], radius: f64, height: f64 },
+    Torus { centre: [f64; 3], major_radius: f64, minor_radius: f64 },
+    Wedge { origin: [f64; 3], size: [f64; 3] },
+}
+
+/// Construction spec for a minimal 2D curve entity (phase-1 set; profiles/inputs).
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub enum Curve2Spec {
+    Line { start: [f64; 3], end: [f64; 3] },
+    Circle { centre: [f64; 3], radius: f64 },
+    Polyline { points: Vec<[f64; 3]>, closed: bool },
+    Point { position: [f64; 3] },
+}
+
+/// A generic entity-construction payload used by the bulk op
+/// [`crate::ops::Operation::CreateMany`]. Mirrors the per-family construction
+/// specs so one bulk op can carry many homogeneous (or mixed) creations.
+#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
+pub enum EntitySpec {
+    Curve(Curve2Spec),
+    Solid(SolidPrimitive),
+}
+
+/// 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.
+#[derive(Debug, Clone, Copy, PartialEq, Serialize, Deserialize)]
+pub struct PlacementSpec {
+    pub x_axis: [f64; 3],
+    pub y_axis: [f64; 3],
+    pub z_axis: [f64; 3],
+    pub origin: [f64; 3],
+}
+
+impl PlacementSpec {
+    /// Identity placement (no transform).
+    pub const IDENTITY: PlacementSpec = PlacementSpec {
+        x_axis: [1.0, 0.0, 0.0],
+        y_axis: [0.0, 1.0, 0.0],
+        z_axis: [0.0, 0.0, 1.0],
+        origin: [0.0, 0.0, 0.0],
+    };
+
+    /// Pure translation to `origin` (axes unchanged).
+    pub fn at(origin: [f64; 3]) -> Self {
+        Self { origin, ..Self::IDENTITY }
+    }
+}
+
+/// The item-count cap for a single bulk op envelope (plan §5.3): bounds
+/// host-side execution time and payload. Over-cap → `ApiError::Validation`.
+pub const BULK_ITEM_CAP: usize = 100_000;
+
+/// Convenience accessors used by the facade/executor.
+impl crate::gen::Operation {
+    /// The op name used in `ApiError::Validation { op, .. }`.
+    pub fn op_name(&self) -> &'static str {
+        use crate::gen::Operation::*;
+        match self {
+            CreateSolid(_) => "CreateSolid",
+            CreateCurve(_) => "CreateCurve",
+            Extrude { .. } => "Extrude",
+            Revolve { .. } => "Revolve",
+            Transform { .. } => "Transform",
+            SolidBoolean { .. } => "SolidBoolean",
+            AddVertex { .. } => "AddVertex",
+            Delete { .. } => "Delete",
+            CreateMany(_) => "CreateMany",
+            TransformMany { .. } => "TransformMany",
+            DeleteMany(_) => "DeleteMany",
+        }
+    }
+}