diff --git a/src/bioetl/application/core/batch_writer_columns_mixin.py b/src/bioetl/application/core/batch_writer_columns_mixin.py
index 718c8b5696..7d49af0ecd 100644
--- a/src/bioetl/application/core/batch_writer_columns_mixin.py
+++ b/src/bioetl/application/core/batch_writer_columns_mixin.py
@@ -3,6 +3,7 @@
 
 from __future__ import annotations
 
+import itertools
 from typing import TYPE_CHECKING, Literal
 
 if TYPE_CHECKING:
@@ -86,14 +87,7 @@ def _get_schema_columns(
 
     def _collect_record_columns(self, records: list[GoldRecord]) -> list[str]:
         """Collect columns in stable first-seen order."""
-        columns: list[str] = []
-        seen: set[str] = set()
-        for record in records:
-            for key in record:
-                if key not in seen:
-                    seen.add(key)
-                    columns.append(key)
-        return columns
+        return list(dict.fromkeys(itertools.chain.from_iterable(records)))
 
     def _get_column_order(self, columns: Sequence[str]) -> list[str] | None:
         """Resolve explicit column order from configured column groups."""
diff --git a/src/bioetl/infrastructure/adapters/common/deduplication.py b/src/bioetl/infrastructure/adapters/common/deduplication.py
index 18e1a8f9b9..3fc438c996 100644
--- a/src/bioetl/infrastructure/adapters/common/deduplication.py
+++ b/src/bioetl/infrastructure/adapters/common/deduplication.py
@@ -35,14 +35,7 @@
 
 def deduplicate_preserving_order(values: Iterable[str]) -> list[str]:
     """Return unique values while preserving the original order."""
-    unique_values: list[str] = []
-    seen_values: set[str] = set()
-    for value in values:
-        if value in seen_values:
-            continue
-        seen_values.add(value)
-        unique_values.append(value)
-    return unique_values
+    return list(dict.fromkeys(values))
 
 
 def iter_deduplicated_records(
diff --git a/src/bioetl/infrastructure/config/base_config_loader.py b/src/bioetl/infrastructure/config/base_config_loader.py
index 48057368dd..cd7a1d1ab8 100644
--- a/src/bioetl/infrastructure/config/base_config_loader.py
+++ b/src/bioetl/infrastructure/config/base_config_loader.py
@@ -144,13 +144,7 @@ def _merge_lists(
         """
         # Default: simple concatenation with deduplication for string lists
         if base and isinstance(base[0], str):
-            seen: set[str] = set()
-            result: list[str] = []
-            for item in base + override:
-                if item not in seen:
-                    seen.add(item)
-                    result.append(item)
-            return result
+            return list(dict.fromkeys(base + override))
         # Non-string lists: just concatenate
         return base + override
 
diff --git a/src/bioetl/infrastructure/config/filter_config_loader.py b/src/bioetl/infrastructure/config/filter_config_loader.py
index a3e073a641..41f64e3c03 100644
--- a/src/bioetl/infrastructure/config/filter_config_loader.py
+++ b/src/bioetl/infrastructure/config/filter_config_loader.py
@@ -304,15 +304,7 @@ def _merge_string_lists(
         Returns:
             Merged list with unique values, base items first.
         """
-        seen: set[str] = set()
-        result: list[str] = []
-
-        for item in base + override:
-            if item not in seen:
-                seen.add(item)
-                result.append(item)
-
-        return result
+        return list(dict.fromkeys(base + override))
 
 
 __all__ = ["FilterConfigLoader"]
diff --git a/src/bioetl/infrastructure/config_merge.py b/src/bioetl/infrastructure/config_merge.py
index 5bbffbaab6..4d337c3369 100644
--- a/src/bioetl/infrastructure/config_merge.py
+++ b/src/bioetl/infrastructure/config_merge.py
@@ -35,14 +35,8 @@ def _default_concat_list_merger(
     if all(isinstance(item, str) for item in base) and all(
         isinstance(item, str) for item in override
     ):
-        seen: set[str] = set()
-        merged: list[Any] = []  # Any: YAML config values are heterogeneous
-        for item in base + override:
-            item_str = str(item)
-            if item_str not in seen:
-                seen.add(item_str)
-                merged.append(item)
-        return merged
+        # Items are already strings, so list(dict.fromkeys(...)) is safe and preserves order.
+        return list(dict.fromkeys(base + override))
 
     return [*base, *override]