Reject IVF binary quantizer when dimensions not divisible by 8

The binary quantizer uses D/8 for buffer sizes and memset, which
truncates for non-multiple-of-8 dimensions, causing OOB writes.
Rather than using ceiling division, enforce the constraint at
table creation time with a clear parse error.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: asg017

sqlite-vec.c

@@ -3074,6 +3074,9 @@ int vec0_parse_vector_column(const char *source, int source_length,
         if (rc != SQLITE_OK) {
           return SQLITE_ERROR;
         }
+        if (ivfConfig.quantizer == VEC0_IVF_QUANTIZER_BINARY && (dimensions % 8) != 0) {
+          return SQLITE_ERROR;
+        }
 #else
         return SQLITE_ERROR; // IVF not compiled in
 #endif

tests/test-ivf-quantization.py

@@ -253,3 +253,20 @@ def test_ivf_quantized_delete(db):
     db.execute("DELETE FROM t WHERE rowid = 5")
     # _ivf_vectors should have 9 rows
     assert db.execute("SELECT count(*) FROM t_ivf_vectors00").fetchone()[0] == 9
+
+
+def test_ivf_binary_rejects_non_multiple_of_8_dims(db):
+    """Binary quantizer requires dimensions divisible by 8."""
+    with pytest.raises(sqlite3.OperationalError):
+        db.execute(
+            "CREATE VIRTUAL TABLE t USING vec0("
+            "  v float[12] indexed by ivf(quantizer=binary)"
+            ")"
+        )
+
+    # Dimensions divisible by 8 should work
+    db.execute(
+        "CREATE VIRTUAL TABLE t2 USING vec0("
+        "  v float[16] indexed by ivf(quantizer=binary)"
+        ")"
+    )