diff --git a/api/alembic/versions/0019_backfill_missing_columns.py b/api/alembic/versions/0019_backfill_missing_columns.py
new file mode 100644
index 0000000..70640bd
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+++ b/api/alembic/versions/0019_backfill_missing_columns.py
@@ -0,0 +1,51 @@
+"""补建缺失列：segments.audio_duration_seconds, conversations.deleted_at
+
+0001 用 create_all 建表，对已有表不会 ALTER 追加列。
+本迁移补齐 ORM 模型中存在但生产库缺失的两列。
+
+Revision ID: 0019_backfill_missing_columns
+Revises: 0018_users_language_preference
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+
+from alembic import op
+
+revision: str = "0019_backfill_missing_columns"
+down_revision: Union[str, None] = "0018_users_language_preference"
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def _column_names(table_name: str) -> set[str]:
+    bind = op.get_bind()
+    inspector = sa.inspect(bind)
+    return {column["name"] for column in inspector.get_columns(table_name)}
+
+
+def upgrade() -> None:
+    seg_cols = _column_names("segments")
+    if "audio_duration_seconds" not in seg_cols:
+        op.add_column(
+            "segments",
+            sa.Column("audio_duration_seconds", sa.Integer(), nullable=True),
+        )
+
+    conv_cols = _column_names("conversations")
+    if "deleted_at" not in conv_cols:
+        op.add_column(
+            "conversations",
+            sa.Column("deleted_at", sa.DateTime(timezone=True), nullable=True),
+        )
+
+
+def downgrade() -> None:
+    conv_cols = _column_names("conversations")
+    if "deleted_at" in conv_cols:
+        op.drop_column("conversations", "deleted_at")
+
+    seg_cols = _column_names("segments")
+    if "audio_duration_seconds" in seg_cols:
+        op.drop_column("segments", "audio_duration_seconds")