diff --git a/docs/CICs/UNFAOPostProcessorManager.md b/docs/CICs/UNFAOPostProcessorManager.md
index 76a7cda..42d31c1 100644
--- a/docs/CICs/UNFAOPostProcessorManager.md
+++ b/docs/CICs/UNFAOPostProcessorManager.md
@@ -77,7 +77,7 @@ Assumptions that are not met **must cause failure**, not fallback behavior. **Kn
 - **Null values in required metadata columns:** Raises `ValueError` with null count and affected column name (C-01 resolved — validation active)
 - **Dataset initialization failure:** Raises `ValueError` in `_save()` if datasets are None
 - **Appwrite upload failure:** Propagates exception from `DatastoreModule`
-- **Wrong forecast file selected:** Raises `ForecastIdentityError` in `_read_forecast_data()` if the newest `category="forecast"` file's identity (name/loa) does not match the configured ensemble (S3/C-25 — a stray upload cannot be silently shipped)
+- **Wrong forecast file selected:** Raises `ForecastIdentityError` in `_read_forecast_data()` if the selected file's identity (name/loa) does not match the configured ensemble (S3/C-25 — a stray upload cannot be silently shipped). Selection pins `{category="forecast", type="ensemble"}` (`LEGACY_FORECAST_FILTERS`) — the ADR-013 §11.4 transition guard: contract artifacts (`sampled_forecast_*`) are unselectable by this legacy reader
 - **Region coverage mismatch:** Raises `CoverageError` in `_check_coverage()` (called from `_validate()`) if a pinned region's delivered cell count is wrong (S1/C-34) or a GAUL-uncovered excluded cell leaks into the delivery (S4/C-30)
 - **Fabricated historical tail:** `_clip_observed_history()` drops months beyond the producer's `last_valid_month_id` so unobserved zero-padding is not shipped as observed history (S2/C-26); **degrades open** (skips the clip with a WARNING) if the boundary cannot be resolved
 - **Upload provenance:** every upload's `description` carries structured provenance (lookup version, region, expected/actual cell counts, unmapped count) via `_delivery_description()` (S5/C-15)
diff --git a/tests/test_selection_guard.py b/tests/test_selection_guard.py
new file mode 100644
index 0000000..05da56a
--- /dev/null
+++ b/tests/test_selection_guard.py
@@ -0,0 +1,41 @@
+"""Golden-string tests for the Hop-A legacy transition guard (ADR-013 §11.4).
+
+The manager cannot be imported in every test environment (it pulls the full
+pipeline-core framework), so — like the design-contract tests — these pin the guard
+at source level: the legacy selection filters must pin BOTH `category` and the legacy
+`type`, so pipeline-core#269's contract uploads (`sampled_forecast_*`) can never be
+selected by the deployed legacy reader.
+"""
+
+import re
+from pathlib import Path
+
+_SRC = (
+    Path(__file__).resolve().parent.parent
+    / "views_postprocessing" / "unfao" / "managers" / "unfao.py"
+).read_text()
+
+
+def test_legacy_forecast_filters_pin_category_and_type():
+    # The golden string (ADR-013 §3.3 spirit): identity of the guard is this exact dict.
+    assert 'LEGACY_FORECAST_FILTERS = {"category": "forecast", "type": "ensemble"}' in _SRC
+
+
+def test_selection_uses_the_guarded_filters():
+    # The store selection must go through the guarded constant — no inline
+    # category-only filter dict may remain on the selection call.
+    assert "get_latest_file_id(filters=LEGACY_FORECAST_FILTERS)" in _SRC
+    assert not re.search(
+        r"get_latest_file_id\(filters=\{[^}]*\}\)", _SRC
+    ), "inline filter dict on the selection call — must use LEGACY_FORECAST_FILTERS"
+
+
+def test_guard_type_is_disjoint_from_contract_vocabulary():
+    # The pinned legacy type must never be one of the contract's types.
+    assert '"type": "ensemble"' in _SRC
+    for contract_type in (
+        "sampled_forecast_shard",
+        "sampled_forecast_manifest",
+        "sampled_forecast_sidecar",
+    ):
+        assert f'"type": "{contract_type}"' not in _SRC
diff --git a/views_postprocessing/unfao/managers/unfao.py b/views_postprocessing/unfao/managers/unfao.py
index c012f25..194d245 100644
--- a/views_postprocessing/unfao/managers/unfao.py
+++ b/views_postprocessing/unfao/managers/unfao.py
@@ -25,6 +25,13 @@
 
 logger = logging.getLogger(__name__)
 
+# Hop-A legacy selection filters (ADR-013 §11.4 transition guard). Declared, not
+# inferred: the legacy production forecast is uploaded by pipeline-core's ensemble run
+# with type="ensemble"; the contract's sampled_forecast_* types are disjoint by design,
+# so pinning the legacy type here makes contract artifacts unselectable by this reader.
+# Golden-string-tested (tests/test_selection_guard.py); change only with ADR-013.
+LEGACY_FORECAST_FILTERS = {"category": "forecast", "type": "ensemble"}
+
 
 class UNFAOPostProcessorManager(PostprocessorManager, ForecastingModelManager):
     def __init__(
@@ -104,13 +111,17 @@ def _read_forecast_data(self):
         try:
             prediction_store_manager = DatastoreModule(appwrite_file_manager_config=appwrite_config)
 
-            # The store is filtered by category alone (newest-wins), so resolve the file,
-            # then verify its identity before delivering it (S3/C-25): a stray upload with
-            # category="forecast" must not be silently shipped as the configured ensemble.
-            file_id = prediction_store_manager.get_latest_file_id(filters={"category": "forecast"})
+            # Resolve the newest legacy forecast, then verify its identity before
+            # delivering it (S3/C-25): a stray upload must not be silently shipped as
+            # the configured ensemble. The `type` pin is the Hop-A legacy transition
+            # guard (ADR-013 §11.4): legacy ensemble forecasts carry type="ensemble"
+            # (pipeline-core EnsemblePathManager._target), disjoint from the contract's
+            # sampled_forecast_* vocabulary — so pipeline-core#269's shard/manifest
+            # uploads can never be selected by this legacy reader.
+            file_id = prediction_store_manager.get_latest_file_id(filters=LEGACY_FORECAST_FILTERS)
             if file_id is None:
                 raise FileNotFoundError(
-                    "No forecast file found in the prediction store (category='forecast')."
+                    f"No forecast file found in the prediction store (filters={LEGACY_FORECAST_FILTERS})."
                 )
             selected = extraction.file_metadata(prediction_store_manager.get_file_metadata(file_id))
             # Identity contract: the producer's FileMetadata `name`/`loa` written on upload