refactor: what counts as an event moves into its own evaluator, so a search can ask the same question the trigger asks

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/condition.cpp

@@ -0,0 +1,49 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: 2026 Martino Ferrari
+
+#include "condition.hpp"
+
+namespace udpscope {
+
+void EventDetector::configure(const EventCondition& c) noexcept {
+  if (c == cond_) return;
+  cond_ = c;
+  reset();
+}
+
+void EventDetector::reset() noexcept {
+  have_prev_ = false;
+  prev_ = 0.0;
+}
+
+double EventDetector::feed(double value, double t) noexcept {
+  if (!have_prev_) {
+    prev_ = value;
+    have_prev_ = true;
+    return kNoEvent;
+  }
+  double event = kNoEvent;
+  switch (cond_.type) {
+    case TriggerType::Edge:
+      event = feed_edge(value, t);
+      break;
+    case TriggerType::PulseWidth:
+    case TriggerType::Window:
+    case TriggerType::Dropout:
+      break;  // implemented in the tasks that add their panel rows
+  }
+  // After the handler: every crossing test above reads `prev_` as the previous sample.
+  prev_ = value;
+  return event;
+}
+
+double EventDetector::feed_edge(double value, double t) noexcept {
+  const bool up = crossed_up(value);
+  const bool down = crossed_down(value);
+  const bool fired = (cond_.edge == TriggerEdge::Rising && up) ||
+                     (cond_.edge == TriggerEdge::Falling && down) ||
+                     (cond_.edge == TriggerEdge::Both && (up || down));
+  return fired ? t : kNoEvent;
+}
+
+}  // namespace udpscope