Reject NaN and Inf in float32 vector input

NaN/Inf values in vectors break heap/sort invariants in KNN, causing
wrong or unpredictable results. Now rejected at parse time in
fvec_from_value() for both blob and JSON text input paths, with a
clear error message identifying the offending element index.

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

sqlite-vec.c

@@ -984,8 +984,18 @@ static int fvec_from_value(sqlite3_value *value, f32 **vector,
       return SQLITE_NOMEM;
     }
     memcpy(buf, blob, bytes);
+    size_t n = bytes / sizeof(f32);
+    for (size_t i = 0; i < n; i++) {
+      if (isnan(buf[i]) || isinf(buf[i])) {
+        *pzErr = sqlite3_mprintf(
+            "invalid float32 vector: element %d is %s",
+            (int)i, isnan(buf[i]) ? "NaN" : "Inf");
+        sqlite3_free(buf);
+        return SQLITE_ERROR;
+      }
+    }
     *vector = buf;
-    *dimensions = bytes / sizeof(f32);
+    *dimensions = n;
     *cleanup = sqlite3_free;
     return SQLITE_OK;
   }
@@ -1053,6 +1063,13 @@ static int fvec_from_value(sqlite3_value *value, f32 **vector,
       }
 
       f32 res = (f32)result;
+      if (isnan(res) || isinf(res)) {
+        sqlite3_free(x.z);
+        *pzErr = sqlite3_mprintf(
+            "invalid float32 vector: element %d is %s",
+            (int)x.length, isnan(res) ? "NaN" : "Inf");
+        return SQLITE_ERROR;
+      }
       array_append(&x, (const void *)&res);
 
       offset += (endptr - ptr);

tests/test-loadable.py

@@ -365,6 +365,34 @@ def test_vec_distance_l1():
     )
 
 
+def test_vec_reject_nan_inf():
+    """NaN and Inf in float32 vectors should be rejected."""
+    import struct, math
+
+    # NaN via blob
+    nan_blob = struct.pack("4f", 1.0, float("nan"), 3.0, 4.0)
+    with pytest.raises(sqlite3.OperationalError, match="NaN"):
+        db.execute("SELECT vec_length(?)", [nan_blob])
+
+    # Inf via blob
+    inf_blob = struct.pack("4f", 1.0, float("inf"), 3.0, 4.0)
+    with pytest.raises(sqlite3.OperationalError, match="Inf"):
+        db.execute("SELECT vec_length(?)", [inf_blob])
+
+    # -Inf via blob
+    ninf_blob = struct.pack("4f", 1.0, float("-inf"), 3.0, 4.0)
+    with pytest.raises(sqlite3.OperationalError, match="Inf"):
+        db.execute("SELECT vec_length(?)", [ninf_blob])
+
+    # NaN via JSON
+    # Note: JSON doesn't have NaN literal, but strtod may parse "NaN"
+    # This tests the blob path which is the primary input method
+
+    # Valid vectors still work
+    ok_blob = struct.pack("4f", 1.0, 2.0, 3.0, 4.0)
+    assert db.execute("SELECT vec_length(?)", [ok_blob]).fetchone()[0] == 4
+
+
 def test_vec_distance_l2():
     vec_distance_l2 = lambda *args, a="?", b="?": db.execute(
         f"select vec_distance_l2({a}, {b})", args