Agents: summarize dropped messages during compaction safeguard pruning (#2418)

src/agents/pi-extensions/compaction-safeguard-runtime.ts

@@ -0,0 +1,34 @@
+export type CompactionSafeguardRuntimeValue = {
+  maxHistoryShare?: number;
+};
+
+// Session-scoped runtime registry keyed by object identity.
+// Follows the same WeakMap pattern as context-pruning/runtime.ts.
+const REGISTRY = new WeakMap<object, CompactionSafeguardRuntimeValue>();
+
+export function setCompactionSafeguardRuntime(
+  sessionManager: unknown,
+  value: CompactionSafeguardRuntimeValue | null,
+): void {
+  if (!sessionManager || typeof sessionManager !== "object") {
+    return;
+  }
+
+  const key = sessionManager as object;
+  if (value === null) {
+    REGISTRY.delete(key);
+    return;
+  }
+
+  REGISTRY.set(key, value);
+}
+
+export function getCompactionSafeguardRuntime(
+  sessionManager: unknown,
+): CompactionSafeguardRuntimeValue | null {
+  if (!sessionManager || typeof sessionManager !== "object") {
+    return null;
+  }
+
+  return REGISTRY.get(sessionManager as object) ?? null;
+}