diff --git a/pstack-evidence.md b/pstack-evidence.md
new file mode 100644
index 000000000..416ce5f12
--- /dev/null
+++ b/pstack-evidence.md
@@ -0,0 +1,7 @@
+# pstack evidence — bm #1853
+
+## Principles applied
+- fix-root-causes: leftover search_index_rebuilt blocks CREATE; drop it before rebuild.
+- Laziness Protocol: one DROP IF EXISTS before CREATE; no broader migration rewrite.
+- Prove It Works / Test Behavior: regression seeds leftover empty FTS5 table and asserts upgrade reaches script_ngrams with rows intact.
+- Read poteto-mode SKILL.md this session (absolute path under pstack cache).
diff --git a/src/basic_memory/alembic/versions/d2e3f4a5b6c7_add_script_ngrams_to_full_text_search.py b/src/basic_memory/alembic/versions/d2e3f4a5b6c7_add_script_ngrams_to_full_text_search.py
index 913297889..8443803dc 100644
--- a/src/basic_memory/alembic/versions/d2e3f4a5b6c7_add_script_ngrams_to_full_text_search.py
+++ b/src/basic_memory/alembic/versions/d2e3f4a5b6c7_add_script_ngrams_to_full_text_search.py
@@ -38,6 +38,10 @@ def rebuild_sqlite_search_index(*, include_script_ngrams: bool) -> None:
         return
 
     script_definition = "script_ngrams," if include_script_ngrams else ""
+    # A killed mid-migration run can leave an empty search_index_rebuilt while
+    # alembic_version stays behind (issue #1853). Drop the leftover so a retry
+    # can CREATE again instead of failing with "table already exists".
+    op.execute("DROP TABLE IF EXISTS search_index_rebuilt")
     op.execute(f"""
         CREATE VIRTUAL TABLE search_index_rebuilt USING fts5(
             id UNINDEXED,
diff --git a/tests/test_script_ngram_search_migration.py b/tests/test_script_ngram_search_migration.py
index 7efe08ed8..a2b877ed2 100644
--- a/tests/test_script_ngram_search_migration.py
+++ b/tests/test_script_ngram_search_migration.py
@@ -101,3 +101,45 @@ def test_postgres_upgrade_and_downgrade_manage_both_script_indexes(monkeypatch)
     assert "idx_search_index_fts_chunks_script_ngrams_fts" in sql
     assert "to_tsvector('simple', script_ngrams)" in sql
     assert "DROP COLUMN IF EXISTS script_ngrams" in sql
+
+def test_sqlite_upgrade_survives_leftover_search_index_rebuilt(tmp_path, monkeypatch) -> None:
+    """Issue #1853: interrupted upgrade left search_index_rebuilt; retry must succeed."""
+    database_path = tmp_path / "leftover-rebuilt.db"
+    engine = create_engine(f"sqlite:///{database_path}")
+    with engine.begin() as connection:
+        connection.exec_driver_sql("""
+            CREATE VIRTUAL TABLE search_index USING fts5(
+                id UNINDEXED, title, content_stems, content_snippet, permalink,
+                file_path UNINDEXED, type UNINDEXED, project_id UNINDEXED,
+                from_id UNINDEXED, to_id UNINDEXED, relation_type UNINDEXED,
+                entity_id UNINDEXED, category UNINDEXED, metadata UNINDEXED,
+                created_at UNINDEXED, updated_at UNINDEXED,
+                tokenize='unicode61 tokenchars 0x2F', prefix='1,2,3,4'
+            )
+        """)
+        connection.exec_driver_sql("""
+            INSERT INTO search_index (id, title, content_stems, project_id)
+            VALUES (1, 'Probe', 'words', 1)
+        """)
+        # Simulate the leftover empty FTS5 table from a killed CREATE.
+        connection.exec_driver_sql(
+            "CREATE VIRTUAL TABLE search_index_rebuilt USING fts5(x)"
+        )
+        monkeypatch.setattr(
+            migration,
+            "op",
+            Operations(MigrationContext.configure(connection)),
+        )
+        migration.upgrade()
+
+    with sqlite3.connect(database_path) as connection:
+        leftover = connection.execute(
+            "SELECT 1 FROM sqlite_master WHERE type = 'table' AND name = 'search_index_rebuilt'"
+        ).fetchone()
+        assert leftover is None
+        columns = [row[1] for row in connection.execute("PRAGMA table_info(search_index)")]
+        assert "script_ngrams" in columns
+        assert connection.execute(
+            "SELECT id, title, script_ngrams FROM search_index"
+        ).fetchall() == [(1, "Probe", "")]
+