Extract elapsedAtLeast to core/util, dedupe the throttle rationale, and correct the alloc-count/PLAN citations

src/core/util/CMakeLists.txt

@@ -5,3 +5,8 @@ reasampler_test(file_bytes LINK file_bytes)
 add_library(curve_law INTERFACE)
 target_include_directories(curve_law INTERFACE ${REASAMPLER_SRC_DIR})
 reasampler_test(curve_law LINK curve_law)
+
+# The GetTickCount()-wraparound-safe throttle-gate test is header-only, hence INTERFACE.
+add_library(elapsed_at_least INTERFACE)
+target_include_directories(elapsed_at_least INTERFACE ${REASAMPLER_SRC_DIR})
+reasampler_test(elapsed_at_least LINK elapsed_at_least)

src/core/util/elapsed_at_least.h

@@ -0,0 +1,19 @@
+#pragma once
+// elapsed_at_least — the ONE "has at least this long passed" test behind every
+// GetTickCount()-style throttle gate (panel_input's detect cadence, panel_drag's tooltip
+// delay). Unsigned subtraction is the deliberate implementation, not an oversight: it is
+// exactly correct across a GetTickCount() wraparound (~49.7 days uptime) because `now -
+// since`, computed mod 2^32, IS the true forward millisecond distance even when `now`'s
+// raw value is numerically less than `since`'s. A signed or `now < since` guard would
+// instead wedge the gate shut for up to the wrap period.
+
+namespace reasampler::util {
+
+// True once at least `interval` ms separate `since` from `now` (both GetTickCount()-style
+// millisecond counters). `since == 0, interval == 0` reads true, so a zero-initialized
+// "last fired" tick opens the gate on its very first call.
+inline bool elapsedAtLeast(unsigned int now, unsigned int since, unsigned int interval) {
+    return now - since >= interval;
+}
+
+}  // namespace reasampler::util