perf(render): in-place GPU wire arena for move/edit (phase 4, OCS_WIRE_GPU_PATCH)

On a geometry edit the resident set gets a fresh content id, so the batched wire
path (build_wire_buffers) re-emits and re-uploads EVERY wire instance — the whole
buffer even when one line moved. Behind the OCS_WIRE_GPU_PATCH flag (default off,
native only), add a persistent per-entity instance arena: one long-lived
VERTEX|COPY_DST instance buffer + its WireConst storage, with a per-entity slab
table. An in-place edit (move / rotate / scale / colour — same segment count)
becomes a queue.write_buffer of just that entity`s slab.

Scope is deliberately IN-PLACE ONLY. draw_depth_map normalises each entity`s
draw-order z-bias by the block`s entity count, so an Add or Remove re-scales EVERY
entity`s z-bias — which a per-slab patch can`t honour — and a segment-count change
relocates the entity. patch() returns false for any of those (and for mesh-edge /
scissored sets), and the caller falls back to the identical full batched rebuild,
so correctness never rides on the fast path. An adversarial review of an earlier
append/tombstone design surfaced exactly these draw-order hazards; restricting to
in-place removes them while keeping the common interactive-edit win.

The Scene hands the changed handles to the arena via model_wire_gpu_patch,
recorded by try_resident_patch for the Model block and matched by content id in
prepare(); scissored paper viewports and mixed 2D/3D sets keep the batched path.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/scene/pipeline/mod.rs

@@ -10,6 +10,11 @@ pub mod mesh_gpu;
 pub mod text_gpu;
 pub mod uniforms;
 pub mod viewcube;
+/// Persistent per-entity wire instance arena (native), enabled by
+/// `OCS_WIRE_GPU_PATCH` — patches one entity's slab via `write_buffer` instead
+/// of re-uploading the whole wire set on an edit.
+#[cfg(not(target_arch = "wasm32"))]
+pub mod wire_arena;
 pub mod wire_gpu;
 
 use iced::wgpu;
@@ -44,7 +49,7 @@ pub struct Pipeline {
     /// xray pipelines). `Some` on native; `None` on web (fat instance, no
     /// storage). Passed to `WireGpu::from_run` / `from_batch` so they can build
     /// each batch's per-wire bind group.
-    wire_const_bgl: Option<wgpu::BindGroupLayout>,
+    pub(crate) wire_const_bgl: Option<wgpu::BindGroupLayout>,
     wipeout_pipeline: wgpu::RenderPipeline,
     /// Phase 4-B — single-draw batched hatch pipeline. Per-instance
     /// data lives in storage buffers; one draw call covers every
@@ -144,6 +149,14 @@ pub struct Pipeline {
     /// their camera uniforms + scissor stay per-slot, only the geometry is
     /// deduplicated. Never mutated in place, only reassigned on content change.
     pub(crate) gpu_wires: std::sync::Arc<Vec<WireGpu>>,
+    /// Persistent per-entity wire instance arena (native, `OCS_WIRE_GPU_PATCH`).
+    /// When active, `gpu_wires` is a thin wrapper over this arena's buffers and an
+    /// edit patches one entity's slab in place instead of rebuilding every wire.
+    #[cfg(not(target_arch = "wasm32"))]
+    pub(crate) wire_arena: Option<wire_arena::WireArena>,
+    /// The Model content id `wire_arena` currently mirrors (`u64::MAX` = none).
+    #[cfg(not(target_arch = "wasm32"))]
+    pub(crate) wire_arena_id: u64,
     /// Pixel scissor rects [x, y, w, h] for viewport-clipped wires. Recomputed each frame.
     wire_pixel_scissors: Vec<Option<[u32; 4]>>,
     /// Ghost copies (25% alpha) of selected wires for the X-ray depth pass.
@@ -1304,6 +1317,10 @@ impl Pipeline {
             blit_uniform_buffer,
             surface_format: format,
             gpu_wires: std::sync::Arc::new(vec![]),
+            #[cfg(not(target_arch = "wasm32"))]
+            wire_arena: None,
+            #[cfg(not(target_arch = "wasm32"))]
+            wire_arena_id: u64::MAX,
             wire_pixel_scissors: vec![],
             gpu_selected_wires: vec![],
             gpu_preview_wires: vec![],