[eric] electron: memory pressure now sheds weight (thumbnails pause, caches drop) instead of growing until macOS kills the app (ENG-320)

electron/memoryRelief.js

@@ -0,0 +1,59 @@
+// Memory pressure stops being a telemetry event and starts being ACTED on (ENG-320).
+//
+// The sensor next door has watched sessions climb to 3-4GB for weeks and only ever reported it:
+// 18 of 57 active users tripped it in one day, and the observed end state is macOS killing the
+// app with NO trace at all (one such death was caught live mid-capturePage under heavy webviews).
+// A silent kill costs the whole session; everything this module gives up under pressure is
+// re-fetchable or cosmetic, which is the whole trade.
+//
+// Levers, in order of engagement when the cap is crossed:
+//   1. thumbnails stop:   capture-page composites GPU surfaces (big transient allocations, and the
+//                         last logged act before the observed silent death); callers already treat
+//                         null as "keep the last preview", so this degrades invisibly
+//   2. HTTP caches drop:  refetchable bytes, same clear the ENG-247 boot sweep does
+//
+// Hysteresis mirrors the sensor: enter at the cap, exit below 80% of it, one action set per
+// episode so a session hovering at the line cannot thrash the caches.
+'use strict';
+
+let p_underPressure = false;
+let p_episodes = 0;
+let p_actions = null;
+
+/** Wire the action set once at boot; separated for tests and so this file stays require-clean. */
+function initMemoryRelief(actions) {
+  p_actions = actions || null;
+}
+
+/** Called by the sensor with every sample. Returns true when the pressure state CHANGED. */
+function updateMemoryPressure(totalMb, capMb) {
+  if (!p_underPressure && totalMb >= capMb) {
+    p_underPressure = true;
+    p_episodes += 1;
+    try { console.error('[memory-relief] entering pressure mode at', totalMb, 'MB (episode', p_episodes + ')'); } catch (_) {}
+    if (p_actions) {
+      try { p_actions.clearCaches && p_actions.clearCaches(); } catch (_) {}
+    }
+    return true;
+  }
+  if (p_underPressure && totalMb < capMb * 0.8) {
+    p_underPressure = false;
+    try { console.error('[memory-relief] pressure cleared at', totalMb, 'MB'); } catch (_) {}
+    return true;
+  }
+  return false;
+}
+
+/** The capture-page gate: while under pressure, thumbnails yield rather than composite. */
+function underMemoryPressure() {
+  return p_underPressure;
+}
+
+/** Test hook. */
+function resetMemoryRelief() {
+  p_underPressure = false;
+  p_episodes = 0;
+  p_actions = null;
+}
+
+module.exports = { initMemoryRelief, updateMemoryPressure, underMemoryPressure, resetMemoryRelief };