diff --git a/src/services/memory/index.js b/src/services/memory/index.js
index 494dc1d..41d8d6a 100644
--- a/src/services/memory/index.js
+++ b/src/services/memory/index.js
@@ -214,7 +214,11 @@ export async function getRelevantMemories(params) {
     return cached;
   }
 
-  const ranked = await filterAndRankMemories([...memoryStore.values()], queryParams);
+  const source = typeof repository.listMemories === 'function'
+    ? await repository.listMemories(queryParams)
+    : [...memoryStore.values()];
+
+  const ranked = await filterAndRankMemories(source, queryParams);
   await updateMemoryUsage(repository, ranked.map((memory) => memory.id));
   cache.set(cacheKey, ranked);
 
diff --git a/test/memory-pinning.test.mjs b/test/memory-pinning.test.mjs
new file mode 100644
index 0000000..2c6ae90
--- /dev/null
+++ b/test/memory-pinning.test.mjs
@@ -0,0 +1,72 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { getRelevantMemories, pinMemory } from '../src/services/memory/index.js';
+
+test('pinMemory pins the memory and clears the cache', async () => {
+  const records = [
+    { id: 'm1', agent_id: 'agent-a', type: 'event', tags: ['ops'], pinned: false, last_seen: 10, merged_into: null },
+  ];
+
+  let listMemoriesCallCount = 0;
+  const repository = {
+    async listMemories() {
+      listMemoriesCallCount++;
+      return records;
+    },
+    async getMemoryById(id) {
+      return records.find((record) => record.id === id) ?? null;
+    },
+    async setPinned(id, pinned) {
+      const index = records.findIndex((record) => record.id === id);
+      if (index < 0) return null;
+      records[index] = { ...records[index], pinned };
+      return records[index];
+    },
+    async updateMemoryUsage() { return null; }
+  };
+
+  // 1. Populate cache
+  await getRelevantMemories({ agent_id: 'agent-a', repository });
+  assert.equal(listMemoriesCallCount, 1, 'Repository should be queried initially');
+
+  // 2. Verify cache hit
+  await getRelevantMemories({ agent_id: 'agent-a', repository });
+  assert.equal(listMemoriesCallCount, 1, 'Repository should NOT be queried on cache hit');
+
+  // 3. Pin memory
+  const pinned = await pinMemory('m1', { repository });
+  assert.ok(pinned);
+  assert.equal(pinned.pinned, true);
+  assert.equal(records[0].pinned, true);
+
+  // 4. Verify cache miss (cleared)
+  await getRelevantMemories({ agent_id: 'agent-a', repository });
+  assert.equal(listMemoriesCallCount, 2, 'Repository should be queried again after cache clear');
+});
+
+test('pinMemory returns null for non-existent ID but still clears cache', async () => {
+  const records = [];
+  let listMemoriesCallCount = 0;
+  const repository = {
+    async listMemories() {
+      listMemoriesCallCount++;
+      return records;
+    },
+    async setPinned(id, pinned) {
+      return null;
+    },
+    async updateMemoryUsage() { return null; }
+  };
+
+  // 1. Populate cache (use different agent_id to avoid cache collision with previous test)
+  await getRelevantMemories({ agent_id: 'agent-b', repository });
+  assert.equal(listMemoriesCallCount, 1);
+
+  // 2. Pin non-existent memory
+  const result = await pinMemory('non-existent', { repository });
+  assert.equal(result, null);
+
+  // 3. Verify cache cleared
+  await getRelevantMemories({ agent_id: 'agent-b', repository });
+  assert.equal(listMemoriesCallCount, 2, 'Cache should be cleared even if ID not found');
+});