refactor(plugin): extract shared session state and decision pruning

plugin/core/session-state.ts

@@ -0,0 +1,31 @@
+import type { Decision } from "../rules.js";
+
+export type DecisionRecord = {
+  decision: Decision;
+  createdAt: number;
+  needsRestore?: boolean;
+};
+
+export const MAX_SESSION_DECISIONS = 2000;
+export const DECISION_TTL_MS = 5 * 60 * 1000;
+
+export const sessionDecision = new Map<string, DecisionRecord>();
+export const sessionAllowed = new Map<string, boolean>();
+export const sessionInjected = new Set<string>();
+export const sessionChannelId = new Map<string, string>();
+export const sessionAccountId = new Map<string, string>();
+export const sessionTurnHandled = new Set<string>();
+
+export function pruneDecisionMap(now = Date.now()): void {
+  for (const [k, v] of sessionDecision.entries()) {
+    if (now - v.createdAt > DECISION_TTL_MS) sessionDecision.delete(k);
+  }
+
+  if (sessionDecision.size <= MAX_SESSION_DECISIONS) return;
+  const keys = sessionDecision.keys();
+  while (sessionDecision.size > MAX_SESSION_DECISIONS) {
+    const k = keys.next();
+    if (k.done) break;
+    sessionDecision.delete(k.value);
+  }
+}