perf: skip the wire partition when a patch cannot change its output

`arena-post partition=55.2ms blocks=5.9ms curves=2.5ms` — the partition is
almost the whole of the 73 ms an arena patch spends after patching, and it
walks all 236 956 resident wires to serve a one-entity change.

Its three consumers here — the instanced, circle and ellipse uploads —
depend only on wires that are block references or analytical curves. A
patch that touches none of those cannot change any of them, so the walk is
skipped and the uploads already on the slot are kept.

Two things make that sound, and both are checked rather than assumed:

**Depths hold still.** The instances bake a draw depth.
`inserted_draw_depth_label` allocates into a reserved gap instead of
renumbering, so adding an entity leaves every other label alone — the
existing doc comment says so and there is now a test. A rebuild from
scratch *can* move them, so `draw_depth_generation` bumps only there, and
a slot reuses its uploads only while that generation is unchanged.

**Contributors are remembered.** `partition_wires` records which handles
fed those three outputs, and the skip requires that no changed handle is
among them and that no changed handle's new wires would join them. That
catches an entity entering the set and an entity leaving it. The
membership test is shared with the walk it decides to skip, so the two
cannot drift, and it is deliberately conservative: a wire that looks
analytical but fails extraction forces a needless re-partition, never a
stale upload.

`arena-post` gains `skipped=` so a run says how often this actually fires
rather than leaving it to be inferred from the timing.

Not verified on a device yet — the headless harness never reaches
`prepare`, so this needs a GUI run on the reproducer to confirm both the
saving and that nothing goes missing on screen.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/scene/pipeline/mod.rs

@@ -251,6 +251,13 @@ pub struct Pipeline {
     pub(crate) wire_arena_fallback_handles: rustc_hash::FxHashSet<acadrust::Handle>,
     /// The Model content id both arenas currently mirror (`u64::MAX` = none).
     pub(crate) wire_arena_id: u64,
+    /// Entities that fed the instanced / circle / ellipse uploads this slot is
+    /// holding. A patch touching none of them cannot change those uploads, so
+    /// the partition walk over the whole resident set can be skipped.
+    pub(crate) partition_contributors: rustc_hash::FxHashSet<acadrust::Handle>,
+    /// The draw-depth generation those uploads baked. A full depth rebuild
+    /// reassigns every label, so they stop being reusable when it moves.
+    pub(crate) partition_depth_generation: u64,
     /// Last content/camera/viewport tuple used to derive visible instance
     /// ranges from the resident arena.
     pub(crate) wire_cull_key: (u64, u64, u32, u32),
@@ -2338,6 +2345,8 @@ impl Pipeline {
             wire_arena_fallback_kind: None,
             wire_arena_fallback_handles: rustc_hash::FxHashSet::default(),
             wire_arena_id: u64::MAX,
+            partition_contributors: rustc_hash::FxHashSet::default(),
+            partition_depth_generation: u64::MAX,
             wire_cull_key: (u64::MAX, u64::MAX, 0, 0),
             hatch_lod_key: (usize::MAX, u64::MAX, 0, 0, false),
             wipeout_lod_key: (usize::MAX, u64::MAX, 0, 0, false),
@@ -4991,6 +5000,8 @@ impl Pipeline {
         self.wire_arena = None;
         self.wire_arena_mesh = None;
         self.wire_arena_id = u64::MAX;
+        self.partition_contributors.clear();
+        self.partition_depth_generation = u64::MAX;
         self.alloc_size = Size::new(0, 0);
         self.shadow_full = None;
         self.background_source_id = usize::MAX;
@@ -5022,6 +5033,8 @@ impl Pipeline {
         self.wire_arena_fallback_kind = None;
         self.wire_arena_fallback_handles.clear();
         self.wire_arena_id = u64::MAX;
+        self.partition_contributors.clear();
+        self.partition_depth_generation = u64::MAX;
 
         self.gpu_selected_wires.clear();
         self.gpu_selected_block_wires.clear();