Bench: Move primitive-Signal benches to top of bench-signal.js

The fresh-take agents (Challenge + Survey + Neutral) all flagged that
set-same-10m and sub-unsub-100k regressing under reference safety is
inexplicable from the primitive-Signal hot path itself (protect()
early-returns before reading this.safety; bytecode is identical to
clone mode).

The convergent hypothesis is that the regression is inherited
cross-bench state: the upstream list-Signal benches do dramatically
different allocation/cloning work in clone vs reference mode, leaving
V8 with different JIT feedback / heap layout / GC pressure when the
primitive benches execute later in the same Chrome session.

Running the primitives first isolates them. If the regressions persist
at the top of the script, the cause is intrinsic to the primitive path.
If they disappear, the cause is cross-bench state — diagnostic, not a
production code change.

Author: jlukic

packages/reactivity/bench/tachometer/bench-signal.js

@@ -21,6 +21,45 @@ const makeRecords = (n) => {
 
 let sink = null;
 
+/*******************************
+      Primitive Signal hot paths
+      (placed first to isolate from
+       cross-bench heap/JIT state)
+*******************************/
+
+// set-same-10m — exercises the equality short-circuit. With no
+// subscribers attached, set(same) collapses to an equality check + early
+// return. V8 JIT inlines aggressively here (each set is ~8ns), so 10M
+// iterations are needed to land above the σ-floor. A regression that
+// bypasses the short-circuit (e.g., always-notify) inflates the per-set
+// cost an order of magnitude and lights up immediately.
+{
+  const sig = new Signal(42);
+  // purpose: Sets a signal to its current value 10000000 times. Exercises the no-op fast path when nothing changes.
+  performance.mark(startMark('set-same-10m'));
+  for (let i = 0; i < 10_000_000; i++) {
+    sig.set(42);
+  }
+  performance.measure('set-same-10m', startMark('set-same-10m'));
+}
+
+// sub-unsub-100k — measures the per-create/per-destroy cost of a
+// subscriber that reads one signal. Components with frequent mount/unmount
+// (modal dialogs, list virtualization, route transitions) hit this path
+// continuously. 100k cycles to clear the σ-floor at ~340ns/cycle.
+{
+  const sig = new Signal(0);
+  // purpose: Creates and tears down a subscriber on one signal across 100000 cycles. Subscription churn cost.
+  performance.mark(startMark('sub-unsub-100k'));
+  for (let i = 0; i < 100_000; i++) {
+    const r = Reaction.create(() => {
+      sink = sig.get();
+    });
+    r.stop();
+  }
+  performance.measure('sub-unsub-100k', startMark('sub-unsub-100k'));
+}
+
 /*******************************
       Reactive machinery
 *******************************/
@@ -223,43 +262,6 @@ let sink = null;
   r.stop();
 }
 
-/*******************************
-      Signal hot paths
-*******************************/
-
-// set-same-10m — exercises the equality short-circuit. With no
-// subscribers attached, set(same) collapses to an equality check + early
-// return. V8 JIT inlines aggressively here (each set is ~8ns), so 10M
-// iterations are needed to land above the σ-floor. A regression that
-// bypasses the short-circuit (e.g., always-notify) inflates the per-set
-// cost an order of magnitude and lights up immediately.
-{
-  const sig = new Signal(42);
-  // purpose: Sets a signal to its current value 10000000 times. Exercises the no-op fast path when nothing changes.
-  performance.mark(startMark('set-same-10m'));
-  for (let i = 0; i < 10_000_000; i++) {
-    sig.set(42);
-  }
-  performance.measure('set-same-10m', startMark('set-same-10m'));
-}
-
-// sub-unsub-100k — measures the per-create/per-destroy cost of a
-// subscriber that reads one signal. Components with frequent mount/unmount
-// (modal dialogs, list virtualization, route transitions) hit this path
-// continuously. 100k cycles to clear the σ-floor at ~340ns/cycle.
-{
-  const sig = new Signal(0);
-  // purpose: Creates and tears down a subscriber on one signal across 100000 cycles. Subscription churn cost.
-  performance.mark(startMark('sub-unsub-100k'));
-  for (let i = 0; i < 100_000; i++) {
-    const r = Reaction.create(() => {
-      sink = sig.get();
-    });
-    r.stop();
-  }
-  performance.measure('sub-unsub-100k', startMark('sub-unsub-100k'));
-}
-
 /*******************************
       Reaction scheduler
 *******************************/