diff --git a/api/models.py b/api/models.py
index 98cf40a5..68f60cc8 100644
--- a/api/models.py
+++ b/api/models.py
@@ -11727,6 +11727,16 @@ def _merge_session_messages_append_only_impl(
             ):
                 continue
             if row_id_fast_path_allowed:
+                # This state row replays the sidecar row it resolved to, so it
+                # consumes that position in the replay sequence exactly like the
+                # ordinary and multimodal-mirror paths do. Without this the
+                # checkpoint never reads as consumed and a later state-only
+                # reply after an edited checkpoint is truncated.
+                if (
+                    state_replay_idx < len(sidecar_visible_messages)
+                    and sidecar_visible_messages[state_replay_idx] is existing
+                ):
+                    state_replay_idx += 1
                 existing_api_content = _session_message_api_content_key(existing)
                 incoming_api_content = _session_message_api_content_key(msg)
                 if (
diff --git a/tests/test_7754_image_row_replay_checkpoint.py b/tests/test_7754_image_row_replay_checkpoint.py
new file mode 100644
index 00000000..066fe269
--- /dev/null
+++ b/tests/test_7754_image_row_replay_checkpoint.py
@@ -0,0 +1,65 @@
+"""#7754: a marked native-image state row that replays its sidecar row must consume that replay slot.
+
+Before the fix, the row-id fast path for a marked native-image mirror row `continue`d without
+advancing the replay index. The edited checkpoint then never read as consumed, and a rerun reply
+that exists only in state.db was truncated. Master (no marker branch) keeps that reply.
+"""
+
+import api.models as models
+
+
+def _merge(*, marked):
+    field = models._WEBUI_UNMATCHED_NATIVE_IMAGE_MIRROR_FIELD
+    image_row = {
+        "role": "user",
+        "content": "look",
+        "timestamp": 860.0,
+        "_state_db_row_id": 42,
+        "api_content": "PAYLOAD-A",
+    }
+    sidecar = [
+        {"role": "user", "content": "u1", "timestamp": 100.0},
+        {"role": "assistant", "content": "a1", "timestamp": 101.0},
+        dict(image_row),
+        {"role": "assistant", "content": "a_img", "timestamp": 861.0},
+        {"role": "user", "content": "uE", "timestamp": 900.0},
+    ]
+    state_image_row = dict(image_row)
+    if marked:
+        state_image_row[field] = True
+    state = [
+        {"role": "user", "content": "u1", "timestamp": 100.0},
+        {"role": "assistant", "content": "a1", "timestamp": 101.0},
+        state_image_row,
+        {"role": "assistant", "content": "a_img", "timestamp": 861.0},
+        {"role": "user", "content": "u_old", "timestamp": 870.0},
+        {"role": "assistant", "content": "a_old", "timestamp": 871.0},
+        {"role": "user", "content": "uE", "timestamp": 900.0},
+        {"role": "assistant", "content": "aE", "timestamp": 901.0},
+    ]
+    return models.merge_session_messages_append_only(
+        sidecar,
+        state,
+        truncation_watermark=900.0,
+        truncation_boundary=861.0,
+        incoming_provenance="state_db",
+    )
+
+
+def _contents(rows):
+    return [row.get("content") for row in rows]
+
+
+def test_marked_image_row_keeps_state_only_reply_after_edited_checkpoint():
+    merged = _merge(marked=True)
+    assert _contents(merged) == ["u1", "a1", "look", "a_img", "uE", "aE"]
+
+
+def test_marked_and_unmarked_image_rows_merge_identically():
+    assert _contents(_merge(marked=True)) == _contents(_merge(marked=False))
+
+
+def test_removed_rows_between_boundary_and_watermark_stay_out():
+    contents = _contents(_merge(marked=True))
+    assert "u_old" not in contents
+    assert "a_old" not in contents