Improve cross_device MemFuse recall with source tags and recallContext.

Auto-enable device/location prefixes for cross_device scenarios, thread question_device into keyword and embedding paths, and boost lexical scores from source-tag tokens.

Co-authored-by: Cursor <cursoragent@cursor.com>

memory-v2-pgvector.test.mjs

@@ -353,6 +353,26 @@ test('extractKeywordTerms prioritizes proper nouns over generic English terms',
   assert.equal(terms.includes('soccer'), true);
 });
 
+test('mergeKeywordTerms prioritizes recallContext device tokens', () => {
+  const { mergeKeywordTerms } = pgvectorMemoryBackendInternals;
+  const terms = mergeKeywordTerms(
+    'What happened this morning?',
+    { device: 'phone_sarah', user: 'Sarah' },
+    { maxTerms: 8 },
+  );
+  assert.equal(terms.includes('sarah'), true);
+  assert.equal(terms.includes('phone'), true);
+  assert.ok(terms.indexOf('phone') < terms.indexOf('morning'));
+});
+
+test('latinWordQueryCoverage boosts tagged device tokens in source prefix', () => {
+  const { latinWordQueryCoverage } = pgvectorMemoryBackendInternals;
+  const query = 'What did Ethan do at soccer practice?';
+  const tagged = '[watch_ethan · field] Ethan fell during soccer practice';
+  const untagged = 'Ethan fell during soccer practice';
+  assert.ok(latinWordQueryCoverage(query, tagged) >= latinWordQueryCoverage(query, untagged));
+});
+
 test('selectKeywordCandidateRows keeps priority-term gold under broad OR truncation', () => {
   const { selectKeywordCandidateRows, extractKeywordTerms } = pgvectorMemoryBackendInternals;
   const query = 'Why did David promise Ethan extra LEGO time on weekends?';