Summary

Adds automatic LRU-style eviction to history maps to prevent unbounded memory growth in long-running instances.

Problem

The groupHistories Map (and similar maps in Signal, WhatsApp, iMessage monitors) grows unbounded as users interact with more groups over time:

const groupHistories = new Map<string, HistoryEntry[]>();

While clearHistoryEntries() empties values, keys are never deleted. Growth is O(unique groups), causing slow but steady memory accumulation.

Solution

Added to src/auto-reply/reply/history.ts:

export const MAX_HISTORY_KEYS = 1000;

export function evictOldHistoryKeys<T>(
  historyMap: Map<string, T[]>,
  maxKeys: number = MAX_HISTORY_KEYS,
): void {
  if (historyMap.size <= maxKeys) return;
  const keysToDelete = historyMap.size - maxKeys;
  const iterator = historyMap.keys();
  for (let i = 0; i < keysToDelete; i++) {
    const key = iterator.next().value;
    if (key !== undefined) historyMap.delete(key);
  }
}

Called automatically in appendHistoryEntry() to bound map size. Uses Map's insertion order for LRU-like behavior.

Benefits

• ✅ Bounds memory growth to ~1000 groups maximum
• ✅ Minimal overhead (only runs when threshold exceeded)
• ✅ Uses existing Map insertion order (no extra data structures)
• ✅ Applies to all channel monitors using the shared history functions

Testing

• ✅ Build passes (pnpm build)
• ✅ Lint passes (pnpm lint)
• 🔍 Lightly tested - verified eviction logic with manual testing

AI Disclosure

This PR was AI-assisted (Claude/Codex). The issue was discovered through automated code analysis comparing memory patterns across long-running instances.

Fixes #2384