From 5d91dcf127a50652a92f940640c41373b1941eb6 Mon Sep 17 00:00:00 2001
From: "Gareth.Y" <91742523+linjiaye929@users.noreply.github.com>
Date: Wed, 28 Oct 2026 21:03:16 -0700
Subject: [PATCH] fix: preserve custom ID case in exported span parents

---
 py/src/braintrust/span_identifier_v4.py   |  6 ++--
 py/src/braintrust/test_span_components.py | 34 +++++++++++++++++++++++
 2 files changed, 38 insertions(+), 2 deletions(-)

diff --git a/py/src/braintrust/span_identifier_v4.py b/py/src/braintrust/span_identifier_v4.py
index a8a67ff99..c0e5f75ac 100644
--- a/py/src/braintrust/span_identifier_v4.py
+++ b/py/src/braintrust/span_identifier_v4.py
@@ -21,7 +21,8 @@ def _try_make_hex_trace_id(s):
         if isinstance(s, str) and len(s) == 32:  # 32 hex chars = 16 bytes
             ret = bytes.fromhex(s)
             assert len(ret) == 16
-            return ret, True
+            if ret.hex() == s:
+                return ret, True
     except Exception:
         pass
     return None, False
@@ -33,7 +34,8 @@ def _try_make_hex_span_id(s):
         if isinstance(s, str) and len(s) == 16:  # 16 hex chars = 8 bytes
             ret = bytes.fromhex(s)
             assert len(ret) == 8
-            return ret, True
+            if ret.hex() == s:
+                return ret, True
     except Exception:
         pass
     return None, False
diff --git a/py/src/braintrust/test_span_components.py b/py/src/braintrust/test_span_components.py
index fa12a94e1..cb83057c6 100644
--- a/py/src/braintrust/test_span_components.py
+++ b/py/src/braintrust/test_span_components.py
@@ -76,6 +76,40 @@ def test_otel_ids_fail_roundtrip(self):
 class TestSpanComponentsV4:
     """Test SpanComponentsV4 functionality and OTEL compatibility."""
 
+    @pytest.mark.parametrize(
+        ("span_id", "root_span_id"),
+        [
+            ("ABCDEF1234567890", "abcdef0123456789abcdef0123456789"),
+            ("abcdef1234567890", "ABCDEF0123456789ABCDEF0123456789"),
+            ("AbCdEf1234567890", "AbCdEf0123456789AbCdEf0123456789"),
+            ("abcdef1234567890", "abcdef0123456789abcdef0123456789"),
+            ("0123456789012345", "01234567890123456789012345678901"),
+            ("custom-span", "custom-root"),
+            ("72EAC0DD-0775-4D40-BAC8-1DFC8CC14059", "72EAC0DD-0775-4D40-BAC8-1DFC8CC14059"),
+        ],
+    )
+    def test_exported_custom_ids_preserve_parent_link(self, span_id, root_span_id, with_memory_logger):
+        from braintrust.test_helpers import init_test_logger, preserve_env_vars
+
+        with preserve_env_vars("BRAINTRUST_LEGACY_IDS"):
+            os.environ.pop("BRAINTRUST_LEGACY_IDS", None)
+            log = init_test_logger("custom-id-roundtrip")
+            with log.start_span(name="parent", span_id=span_id, root_span_id=root_span_id) as parent:
+                exported = parent.export()
+            with log.start_span(name="child", parent=exported):
+                pass
+
+        rows = with_memory_logger.pop()
+        parent_row = next(row for row in rows if row["span_attributes"]["name"] == "parent")
+        child_row = next(row for row in rows if row["span_attributes"]["name"] == "child")
+        assert parent_row["span_id"] == span_id
+        assert parent_row["root_span_id"] == root_span_id
+        assert child_row["span_parents"] == [parent_row["span_id"]]
+        assert child_row["root_span_id"] == parent_row["root_span_id"]
+        decoded = SpanComponentsV4.from_str(exported)
+        assert decoded.span_id == span_id
+        assert decoded.root_span_id == root_span_id
+
     def test_otel_hex_strings_preserved(self):
         """Test that V4 preserves OTEL hex strings exactly."""
         otel_gen = OTELIDGenerator()