feat(agent): opt-in tool-result context pruning

src/agents/pi-extensions/context-pruning/runtime.ts

@@ -0,0 +1,39 @@
+import type { EffectiveContextPruningSettings } from "./settings.js";
+
+export type ContextPruningRuntimeValue = {
+  settings: EffectiveContextPruningSettings;
+  contextWindowTokens?: number | null;
+  isToolPrunable: (toolName: string) => boolean;
+};
+
+// Session-scoped runtime registry keyed by object identity.
+// Important: this relies on Pi passing the same SessionManager object instance into
+// ExtensionContext (ctx.sessionManager) that we used when calling setContextPruningRuntime.
+const REGISTRY = new WeakMap<object, ContextPruningRuntimeValue>();
+
+export function setContextPruningRuntime(
+  sessionManager: unknown,
+  value: ContextPruningRuntimeValue | 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 getContextPruningRuntime(
+  sessionManager: unknown,
+): ContextPruningRuntimeValue | null {
+  if (!sessionManager || typeof sessionManager !== "object") {
+    return null;
+  }
+
+  return REGISTRY.get(sessionManager as object) ?? null;
+}