diff --git a/infrastructure/chatgpt/chatgpt_column_classifier.py b/infrastructure/chatgpt/chatgpt_column_classifier.py
index 15389184..a42b9b4b 100644
--- a/infrastructure/chatgpt/chatgpt_column_classifier.py
+++ b/infrastructure/chatgpt/chatgpt_column_classifier.py
@@ -5,8 +5,8 @@ from enum import Enum
 from typing import Any, Optional, TypeVar
 
 from infrastructure.column_classifier import (
+    BaseColumnClassifier,
     ClassificationError,
-    ColumnClassifier,
 )
 from infrastructure.chatgpt.chatgpt import ChatGPT
 from infrastructure.chatgpt.exceptions import ChatGPTClientError
@@ -14,7 +14,7 @@ from infrastructure.chatgpt.exceptions import ChatGPTClientError
 E = TypeVar("E", bound=Enum)
 
 
-class ChatGptColumnClassifier(ColumnClassifier[E]):
+class ChatGptColumnClassifier(BaseColumnClassifier[E]):
     """ColumnClassifier backed by ChatGPT, parametrised by a category enum.
 
     The same classification path -- prompt, JSON parsing, UNKNOWN fallback --
diff --git a/infrastructure/column_classifier.py b/infrastructure/column_classifier.py
index adc88c6a..b16fd8c0 100644
--- a/infrastructure/column_classifier.py
+++ b/infrastructure/column_classifier.py
@@ -16,12 +16,14 @@ class ClassificationError(Exception):
     """
 
 
-class ColumnClassifier(ABC, Generic[E]):
-    """Port: resolves free-text descriptions into a category enum ``E``.
+class BaseColumnClassifier(ABC, Generic[E]):
+    """Adapter base: shared scaffolding for concrete column classifiers.
 
     One classifier handles one landlord-CSV column. Implementations decide
-    *how* the mapping is performed (an LLM, a lookup table, a rules engine);
-    ``LandlordDescriptionOverridesOrchestrator`` depends only on this interface.
+    *how* the mapping is performed (an LLM, a lookup table, a rules engine).
+    Consumers do not depend on this class -- they depend on the structural
+    ``ColumnClassifier`` Protocol declared in the orchestration layer; this
+    ABC merely gives adapters a common base for the ``classify`` contract.
     """
 
     @abstractmethod
diff --git a/orchestration/classifiable_column.py b/orchestration/classifiable_column.py
index 9b6fda10..b8aeb08a 100644
--- a/orchestration/classifiable_column.py
+++ b/orchestration/classifiable_column.py
@@ -2,9 +2,8 @@ from __future__ import annotations
 
 from dataclasses import dataclass
 from enum import Enum
-from typing import Generic, TypeVar
+from typing import Generic, Protocol, TypeVar, runtime_checkable
 
-from infrastructure.column_classifier import ColumnClassifier
 from repositories.landlord_overrides.landlord_override_repository import (
     LandlordOverrideRepository,
 )
@@ -12,6 +11,26 @@ from repositories.landlord_overrides.landlord_override_repository import (
 E = TypeVar("E", bound=Enum)
 
 
+@runtime_checkable
+class ColumnClassifier(Protocol[E]):
+    """Port: resolves free-text descriptions into a category enum ``E``.
+
+    The orchestration layer owns this contract because it is the consumer.
+    Any object exposing a matching ``classify`` satisfies it structurally --
+    e.g. ``infrastructure.chatgpt.ChatGptColumnClassifier`` -- so orchestration
+    never imports an adapter.
+    """
+
+    def classify(self, descriptions: set[str]) -> dict[str, E]:
+        """Classify each description into a category enum member.
+
+        Every input description appears as a key in the result. A description
+        that cannot be resolved maps to the enum's UNKNOWN member. A wholesale
+        failure raises the adapter's ``ClassificationError``.
+        """
+        ...
+
+
 @dataclass(frozen=True)
 class ClassifiableColumn(Generic[E]):
     """Pairs a column's classifier with the repository that persists its results.
diff --git a/tests/orchestration/test_landlord_description_overrides_orchestrator.py b/tests/orchestration/test_landlord_description_overrides_orchestrator.py
index 18188941..1b9785c9 100644
--- a/tests/orchestration/test_landlord_description_overrides_orchestrator.py
+++ b/tests/orchestration/test_landlord_description_overrides_orchestrator.py
@@ -5,11 +5,10 @@ from typing import Any, Optional
 
 from domain.addresses.unstandardised_address import AddressList, UnstandardisedAddress
 from domain.epc.built_form_type import BuiltFormType
-from infrastructure.column_classifier import ColumnClassifier
 from domain.epc.property_type import PropertyType
 from domain.epc.wall_type import WallType
 from domain.postcode import Postcode
-from orchestration.classifiable_column import ClassifiableColumn
+from orchestration.classifiable_column import ClassifiableColumn, ColumnClassifier
 from orchestration.landlord_description_overrides_orchestrator import (
     LandlordDescriptionOverridesOrchestrator,
 )