diff --git a/core/wren/src/wren/genbi/composer.py b/core/wren/src/wren/genbi/composer.py
index 726b8d5860..f4afc11c11 100644
--- a/core/wren/src/wren/genbi/composer.py
+++ b/core/wren/src/wren/genbi/composer.py
@@ -51,14 +51,21 @@ def _data_mode_guidance(data_mode: str) -> str:
     raise ValueError(f"unknown data-mode {data_mode!r}; expected one of {DATA_MODES}")
 
 
-def _format_model_inventory(models: list[dict]) -> str:
+def _format_model_inventory(models: list[dict] | None) -> str:
     """One markdown bullet per model with its column names."""
     if not models:
         return "- (no models found — run `wren context build` first)"
     lines = []
     for model in models:
-        cols = ", ".join(c.get("name", "?") for c in model.get("columns", []))
+        if not isinstance(model, dict):
+            continue
+        raw_cols = model.get("columns") or []
+        if not isinstance(raw_cols, list):
+            raw_cols = []
+        cols = ", ".join(c.get("name", "?") for c in raw_cols if isinstance(c, dict))
         lines.append(f"- **{model.get('name', '?')}**: {cols}")
+    if not lines:
+        return "- (no models found — run `wren context build` first)"
     return "\n".join(lines)
 
 
diff --git a/core/wren/tests/unit/test_genbi_format_model_inventory.py b/core/wren/tests/unit/test_genbi_format_model_inventory.py
new file mode 100644
index 0000000000..b8415d81ed
--- /dev/null
+++ b/core/wren/tests/unit/test_genbi_format_model_inventory.py
@@ -0,0 +1,30 @@
+from wren.genbi.composer import _format_model_inventory
+
+
+def test_formats_clean_models():
+    text = _format_model_inventory(
+        [{"name": "orders", "columns": [{"name": "id"}, {"name": "total"}]}]
+    )
+    assert "orders" in text
+    assert "id" in text
+
+
+def test_skips_non_dict_models_and_columns():
+    text = _format_model_inventory(
+        [
+            None,
+            "x",
+            {
+                "name": "t",
+                "columns": [None, {"name": "a"}, "bad"],
+            },
+        ]
+    )
+    assert "t" in text
+    assert "a" in text
+    assert "None" not in text
+
+
+def test_all_junk_falls_back_to_empty_message():
+    text = _format_model_inventory([None, "x", 1])
+    assert "no models found" in text