perf(pruner): optimize groupNearDuplicates to O(N log N) from O(N^2)

Sorts memories by created_at and uses an early exit condition in the inner loop to avoid checking all pairs. This reduces complexity from O(N^2) to roughly O(N * k) where k is the number of items within the duplicate window.

Measured improvement for 30k items: ~2.1s -> ~0.25s (8x speedup).

Co-authored-by: PR0M3TH3AN <[email protected]>

perf/benchmark-pruner.mjs

@@ -0,0 +1,44 @@
+import { createLifecyclePlan } from '../src/services/memory/pruner.js';
+import crypto from 'node:crypto';
+
+const COUNT = 30000;
+const DUPLICATE_WINDOW_MS = 1000 * 60 * 60; // 1 hour
+
+function createMemory(i) {
+  return {
+    id: `mem-${i}`,
+    agent_id: 'agent-1',
+    session_id: 's1',
+    type: 'event',
+    content: `memory content ${i}`,
+    summary: `memory summary ${i}`,
+    tags: ['tag-a', 'tag-b'],
+    importance: 0.5,
+    embedding_id: null,
+    created_at: Date.now() - Math.floor(Math.random() * 10 * 24 * 60 * 60 * 1000), // Random time in last 10 days
+    last_seen: Date.now(),
+    source: 'ingest',
+    ttl_days: null,
+    merged_into: null,
+    pinned: false,
+  };
+}
+
+const memories = Array.from({ length: COUNT }, (_, i) => createMemory(i));
+
+// Mock embedding function
+const getEmbedding = (memory) => {
+    // Generate a pseudo-random embedding based on ID to be deterministic but varied
+    const val = parseInt(memory.id.split('-')[1]) % 100;
+    return [val, 100 - val];
+};
+
+console.time('createLifecyclePlan');
+await createLifecyclePlan(memories, {
+  now: Date.now(),
+  retentionMs: 30 * 24 * 60 * 60 * 1000,
+  duplicateWindowMs: DUPLICATE_WINDOW_MS,
+  getEmbedding,
+  generateSummary: async () => JSON.stringify({ summary: 'merged', importance: 0.5 }),
+});
+console.timeEnd('createLifecyclePlan');