diff --git a/src/services/sqlite/observations/store.ts b/src/services/sqlite/observations/store.ts
index 20727332..e012ed56 100644
--- a/src/services/sqlite/observations/store.ts
+++ b/src/services/sqlite/observations/store.ts
@@ -22,7 +22,7 @@ export function computeObservationContentHash(
   narrative: string | null
 ): string {
   return createHash('sha256')
-    .update((memorySessionId || '') + (title || '') + (narrative || ''))
+    .update([memorySessionId || '', title || '', narrative || ''].join('\x00'))
     .digest('hex')
     .slice(0, 16);
 }
diff --git a/tests/sqlite/data-integrity.test.ts b/tests/sqlite/data-integrity.test.ts
index 81204d99..307c4600 100644
--- a/tests/sqlite/data-integrity.test.ts
+++ b/tests/sqlite/data-integrity.test.ts
@@ -69,6 +69,16 @@ describe('TRIAGE-03: Data Integrity', () => {
       expect(hash.length).toBe(16);
     });
 
+    it('computeObservationContentHash avoids collision from field boundary ambiguity', () => {
+      // These tuples would collide without a delimiter between fields
+      const hash1 = computeObservationContentHash('session-abc', 'debug log', '');
+      const hash2 = computeObservationContentHash('session-ab', 'cdebug log', '');
+      const hash3 = computeObservationContentHash('session-', 'abcdebug log', '');
+      const hash4 = computeObservationContentHash('', 'session-abcdebug log', '');
+      const hashes = new Set([hash1, hash2, hash3, hash4]);
+      expect(hashes.size).toBe(4);
+    });
+
     it('storeObservation deduplicates identical observations within 30s window', () => {
       const memId = createSessionWithMemoryId(db, 'content-dedup-1', 'mem-dedup-1');
       const obs = createObservationInput({ title: 'Same Title', narrative: 'Same Narrative' });