fix(sidebar): keep multiple messageful imported/CLI sessions discoverable (#4218) (#4232)

* Fix imported lineage sidebar discoverability

* chore(release): stamp v0.51.429 (Release OP) for #4218

---------

Co-authored-by: Dennis Soong <dso2ng@gmail.com>
Co-authored-by: nesquena-hermes <agent@nesquena-hermes>

CHANGELOG.md

@@ -3,6 +3,12 @@
 
 ## [Unreleased]
 
+## [v0.51.429] — 2026-06-15 — Release OP (preserve multiple messageful imported/CLI sessions in the sidebar)
+
+### Fixed
+
+- **Multiple imported / CLI sessions that share a lineage with a fuller pre-compression snapshot are no longer collapsed out of the sidebar.** The sidebar's "prefer the fuller snapshot" grouping would hide continuation rows behind a single snapshot even when several of those rows actually have their own messages — making real sessions undiscoverable. Now, when more than one messageful session shares the lineage, the continuations are kept visible; the single-inactive-continuation replacement and the fuller-snapshot preference (when only one row has messages) are unchanged. (#4218)
+
 ## [v0.51.428] — 2026-06-15 — Release OO (bound non-git project-context file walk, #4164)
 
 ### Fixed

api/models.py

@@ -2716,6 +2716,13 @@ def _prefer_fuller_snapshots_for_sidebar(sessions: list[dict]) -> list[dict]:
         if newest_visible_ts > snapshot_ts:
             continue
 
+        messageful_visible = [
+            session for session in visible
+            if _sidebar_message_count(session) > 0
+        ]
+        if len(messageful_visible) > 1:
+            continue
+
         continuation_ids_to_hide.update(
             str(session.get('session_id'))
             for session in visible

tests/test_session_discoverability_invariants.py

@@ -60,3 +60,54 @@ def test_intentional_background_sessions_are_not_rescued_into_sidebar():
     )
 
     assert result == []
+
+
+def _lineage_row(session_id, *, root="lineage", count=1, ts=1.0, snapshot=False, source="cli"):
+    return {
+        "session_id": session_id,
+        "title": session_id,
+        "source_tag": source,
+        "session_source": source,
+        "_lineage_root_id": root,
+        "message_count": count,
+        "user_message_count": 1 if count else 0,
+        "last_message_at": ts,
+        "updated_at": ts,
+        "pre_compression_snapshot": snapshot,
+    }
+
+
+def test_fuller_snapshot_does_not_hide_multirow_imported_cli_lineage():
+    """Multiple messageful imported/CLI rows in one lineage are user-facing segments."""
+    from api.models import _prefer_fuller_snapshots_for_sidebar
+
+    rows = [
+        _lineage_row("imported-a", count=3, ts=100.0),
+        _lineage_row("imported-b", count=4, ts=200.0),
+        _lineage_row("snapshot", count=20, ts=300.0, snapshot=True),
+    ]
+
+    result = _prefer_fuller_snapshots_for_sidebar(rows)
+
+    assert [row["session_id"] for row in result] == [
+        "imported-a",
+        "imported-b",
+        "snapshot",
+    ]
+    snapshot = next(row for row in result if row["session_id"] == "snapshot")
+    assert snapshot["_show_pre_compression_snapshot"] is True
+
+
+def test_fuller_snapshot_still_replaces_single_inactive_continuation():
+    """The existing single-continuation cleanup stays intact."""
+    from api.models import _prefer_fuller_snapshots_for_sidebar
+
+    rows = [
+        _lineage_row("continuation", count=3, ts=100.0, source="webui"),
+        _lineage_row("snapshot", count=20, ts=300.0, snapshot=True, source="webui"),
+    ]
+
+    result = _prefer_fuller_snapshots_for_sidebar(rows)
+
+    assert [row["session_id"] for row in result] == ["snapshot"]
+    assert result[0]["_show_pre_compression_snapshot"] is True