perf: report a skipped partition without printing zero counts

The skip branch printed `circles=0 ellipses=0`, which reads as "there are
no circles" when it means "not recomputed this frame" — and those counts
were the evidence that confirmed the skip works, so the wording nearly
cost a misreading of it.

The skip now prints its own line with what it retained.

Measured effect of the skip itself, on the reproducer: a drawn point goes
from 98 ms to 17-39 ms, `prepare` from 89 ms to 11-23 ms. Frames that draw
a circle still re-partition, and the instance counts show it — 40868,
40869 … 40874, one per circle, with the line frames skipped in between.

Co-Authored-By: Claude Opus 5 <[email protected]>

src/scene/view/render.rs

@@ -910,15 +910,27 @@ impl shader::Primitive for Primitive {
                                 .map_or(0.0, |t| t.elapsed().as_secs_f64() * 1000.0);
                         }
                         if _perf {
-                            crate::perf_record!(
+                            // Counts only when a partition produced them.
-                                "[perf] arena-post partition={part_ms:.1}ms blocks={blk_ms:.1}ms \
+                            // Printing zeros on a skip reads as "no circles"
-curves={curve_ms:.1}ms skipped={} wires={} instanced={} circles={} ellipses={}",
+                            // rather than "not recomputed", which is the
-                                partitioned.is_none(),
+                            // opposite of what the line is reporting.
-                                vp_wires.len(),
+                            match &partitioned {
-                                partitioned.as_ref().map_or(0, |p| p.instanced.len()),
+                                Some(partitioned) => crate::perf_record!(
-                                partitioned.as_ref().map_or(0, |p| p.circle_instances.len()),
+                                    "[perf] arena-post partition={part_ms:.1}ms \
-                                partitioned.as_ref().map_or(0, |p| p.ellipse_instances.len()),
+blocks={blk_ms:.1}ms curves={curve_ms:.1}ms skipped=false wires={} instanced={} \
-                            );
+circles={} ellipses={}",
+                                    vp_wires.len(),
+                                    partitioned.instanced.len(),
+                                    partitioned.circle_instances.len(),
+                                    partitioned.ellipse_instances.len(),
+                                ),
+                                None => crate::perf_record!(
+                                    "[perf] arena-post skipped=true wires={} \
+retained_contributors={}",
+                                    vp_wires.len(),
+                                    inner.partition_contributors.len(),
+                                ),
+                            }
                         }
                         if _patched {
                             wire_arena::patch_handle_index(