ocs_doc_api: fix branch-review findings (tab auth, bulge center, budget, caps, dead code)

CRITICAL:
- execute_doc_api: reject tab_id != bound tab (confused deputy); test
  doc_api_tab_mismatch_is_rejected.
- bulge_arc_segment: fix negative/CW bulge center (apothem magnitude + sign picks
  side; was double-sign-mirrored); test CW-vs-CCW center offset.
- cold-tess budget: move mass_cache/cold_tess_used to per-tab Scene so the budget
  persists across DocApi dispatches (was reset per request); budget-exhausted ->
  approximate meshes.metrics fallback instead of error.

WARNING:
- Loft: add BULK_ITEM_CAP (was uncapped -> unbounded kernel call from one request).
- CreateMany: pre-validate EntitySpec::Curve (ellipse ratio) in prepare phase ->
  all-or-nothing restored; regression test.
- Partial Ellipse: offset start/end_parameter by rot_z on rotation; regression test.
- resolve_body: add with_body borrow accessor (host overrides to borrow cache in
  place, O(1)); bounds() uses it instead of deep-cloning the B-rep per query.
- add_raster_image: validate file path (non-empty, image extension, reject
  UNC/traversal); regression test.

SUGGESTION:
- deploy: bump API_VERSION 5 -> 6 so DocApi plugins are gated at handshake on old
  hosts (append-only wire + defaulted method keep old V2-V5 plugins loading).
- dead code: wire query_name into apply_queries error labels; host uses crate's
  ObjectId::from_handle/to_handle (drop local duplicates); delete is_null/backend_mut.
- mock drift: test mock now stores curve specs + computes curve bounds (aligns with
  example mock); Spline/Dimension bounds delegate to points_aabb.

623 host lib + 8 crate + 3 consistency + 34 plugin_api green.

src/scene/mod.rs

@@ -1804,6 +1804,14 @@ pub struct Scene {
     pub block_meshes: HashMap<Handle, MeshLodSet>,
     /// Kernel B-reps used by solid operations and exact-geometry saves.
     pub solid_models: HashMap<Handle, cadkernel::brep::Body>,
+    /// Memoized DocApi volume/centroid per (handle, geometry_epoch) so repeated
+    /// mass queries on the same solid are O(1). Persists across DocApi dispatches.
+    #[cfg(not(target_arch = "wasm32"))]
+    pub doc_api_mass_cache: std::collections::HashMap<Handle, (u64, f64, [f64; 3])>,
+    /// Per-tab cold-tessellation budget for expensive DocApi volume/centroid
+    /// computations (bounded DoS surface). Persists across DocApi dispatches.
+    #[cfg(not(target_arch = "wasm32"))]
+    pub doc_api_cold_tess_used: usize,
     /// GPU render data for raster images (RasterImage entities), keyed by handle.
     pub images: HashMap<Handle, ImageModel>,
     /// The viewport that is currently "entered" (MSPACE mode).
@@ -2067,6 +2075,10 @@ impl Scene {
             material_base_dir: None,
             block_meshes: HashMap::default(),
             solid_models: HashMap::default(),
+            #[cfg(not(target_arch = "wasm32"))]
+            doc_api_mass_cache: std::collections::HashMap::default(),
+            #[cfg(not(target_arch = "wasm32"))]
+            doc_api_cold_tess_used: 0,
             images: HashMap::default(),
             active_viewport: None,
             bg_color: [33.0 / 255.0, 40.0 / 255.0, 48.0 / 255.0, 1.0],