fix: latch is_sidechain independently of created_at; update list_sessions_from_store docstring

Author: qing-ant

src/claude_agent_sdk/_internal/session_summary.py

@@ -140,10 +140,10 @@ def fold_session_summary(
         if ms is not None and ms > summary["mtime"]:
             summary["mtime"] = ms
 
-        if "created_at" not in summary:
-            if ms is not None:
-                summary["created_at"] = ms
+        if "is_sidechain" not in summary:
             summary["is_sidechain"] = entry.get("isSidechain") is True
+        if "created_at" not in summary and ms is not None:
+            summary["created_at"] = ms
 
         if "cwd" not in summary:
             cwd = entry.get("cwd")

src/claude_agent_sdk/_internal/sessions.py

@@ -1548,11 +1548,11 @@ async def list_sessions_from_store(
         the store path — the store operates on a single ``project_key``.
 
     .. note::
-        This performs one full ``store.load()`` per session in the listing
-        to derive summaries. On remote backends with many or large sessions
-        this can be expensive (e.g., S3 egress, Postgres large-row reads).
-        Consider denormalizing summary metadata into your adapter's
-        ``list_sessions()`` index.
+        If the store implements ``list_session_summaries``, this is a single
+        store call. Otherwise falls back to one ``store.load()`` per session
+        (bounded at 16 concurrent), which on remote backends with many or
+        large sessions can be expensive (e.g., S3 egress, Postgres large-row
+        reads).
     """
     project_path = _canonicalize_path(str(directory) if directory is not None else ".")
     project_key = _sanitize_path(project_path)

tests/test_session_summary.py

@@ -153,6 +153,21 @@ def test_sidechain_from_first_entry(self) -> None:
         )
         assert s["is_sidechain"] is True
 
+    def test_sidechain_latched_when_first_entry_lacks_timestamp(self) -> None:
+        """Regression: is_sidechain must latch on entry 0 even if its timestamp
+        is absent/unparseable, so entry 1 cannot overwrite it to False."""
+        s = fold_session_summary(
+            None,
+            KEY,
+            [
+                {"type": "user", "isSidechain": True},
+                {"type": "x", "timestamp": "2024-01-01T00:00:00Z"},
+            ],
+        )
+        assert s["is_sidechain"] is True
+        # created_at still picks up the first parseable timestamp.
+        assert s["created_at"] == 1704067200000
+
     def test_first_prompt_skips_meta_tool_result_and_compact(self) -> None:
         s = fold_session_summary(
             None,