diff --git a/src/ifcedit/ifcedit/coerce.py b/src/ifcedit/ifcedit/coerce.py
index 0e92bded6d..4a48925293 100644
--- a/src/ifcedit/ifcedit/coerce.py
+++ b/src/ifcedit/ifcedit/coerce.py
@@ -25,13 +25,21 @@ import typing
 import ifcopenshell
 
 
-def coerce_value(value_str: str, type_hint, model: ifcopenshell.file | None = None):
+def coerce_value(
+    value_str: str,
+    type_hint,
+    model: ifcopenshell.file | None = None,
+    lookup_file: ifcopenshell.file | None = None,
+):
     """Convert a CLI string argument to the proper Python type based on a type hint.
 
     Args:
         value_str: The raw string from the CLI.
         type_hint: The type annotation from the function signature.
-        model: An open IFC model, needed to resolve entity instance references by ID.
+        model: The main open IFC model, needed to resolve entity instance references by ID.
+        lookup_file: Override file for entity resolution (e.g. a library file for
+            project.append_asset). When provided, entity IDs are looked up here instead
+            of in model.
 
     Returns:
         The converted Python value.
@@ -40,6 +48,9 @@ def coerce_value(value_str: str, type_hint, model: ifcopenshell.file | None = No
         ValueError: If the value cannot be converted.
         TypeError: If the type hint is not supported.
     """
+    # When a library file has been opened, entity IDs are resolved from it, not the main model.
+    effective_lookup = lookup_file if lookup_file is not None else model
+
     if type_hint is None:
         return value_str
 
@@ -55,7 +66,7 @@ def coerce_value(value_str: str, type_hint, model: ifcopenshell.file | None = No
         # Try each non-None type in order
         for t in non_none_types:
             try:
-                return coerce_value(value_str, t, model)
+                return coerce_value(value_str, t, model, lookup_file)
             except (ValueError, TypeError):
                 continue
         raise ValueError(f"Cannot convert '{value_str}' to any of {non_none_types}")
@@ -73,10 +84,10 @@ def coerce_value(value_str: str, type_hint, model: ifcopenshell.file | None = No
     # list types
     if origin is list:
         if args and _is_entity_type(args[0]):
-            return _coerce_entity_list(value_str, model)
+            return _coerce_entity_list(value_str, effective_lookup)
         if args:
             items = _split_list(value_str)
-            return [coerce_value(item.strip(), args[0], model) for item in items]
+            return [coerce_value(item.strip(), args[0], model, lookup_file) for item in items]
         return _split_list(value_str)
 
     # dict types
@@ -93,9 +104,13 @@ def coerce_value(value_str: str, type_hint, model: ifcopenshell.file | None = No
     if type_hint is bool:
         return value_str.lower() in ("true", "1", "yes")
 
+    # ifcopenshell.file — open from path string
+    if type_hint is ifcopenshell.file:
+        return ifcopenshell.open(value_str)
+
     # entity_instance
     if _is_entity_type(type_hint):
-        return _coerce_entity(value_str, model)
+        return _coerce_entity(value_str, effective_lookup)
 
     # Fallback: try json.loads for complex types, then plain string
     try:
@@ -113,24 +128,24 @@ def _is_entity_type(hint) -> bool:
     return False
 
 
-def _coerce_entity(value_str: str | int, model: ifcopenshell.file | None) -> ifcopenshell.entity_instance:
+def _coerce_entity(value_str: str | int, lookup_file: ifcopenshell.file | None) -> ifcopenshell.entity_instance:
     """Resolve a step ID string like '123' or '#123' to an entity instance."""
-    if model is None:
+    if lookup_file is None:
         raise ValueError("Cannot resolve entity reference without an IFC model")
     if isinstance(value_str, int):
         entity_id = value_str
     else:
         entity_id = int(value_str.strip().lstrip("#"))
     try:
-        return model.by_id(entity_id)
+        return lookup_file.by_id(entity_id)
     except RuntimeError:
         raise ValueError(f"Entity #{entity_id} not found in model")
 
 
-def _coerce_entity_list(value_str: str, model: ifcopenshell.file | None) -> list[ifcopenshell.entity_instance]:
+def _coerce_entity_list(value_str: str, lookup_file: ifcopenshell.file | None) -> list[ifcopenshell.entity_instance]:
     """Resolve a comma-separated list of step IDs to entity instances."""
     items = _split_list(value_str)
-    return [_coerce_entity(item.strip(), model) for item in items]
+    return [_coerce_entity(item.strip(), lookup_file) for item in items]
 
 
 def _split_list(value_str: str) -> list[str]:
diff --git a/src/ifcedit/ifcedit/discover.py b/src/ifcedit/ifcedit/discover.py
index 3059b3b363..3828cf989b 100644
--- a/src/ifcedit/ifcedit/discover.py
+++ b/src/ifcedit/ifcedit/discover.py
@@ -165,10 +165,15 @@ def _extract_params(fn) -> list[dict]:
 
 def _format_type_hint(hint) -> str | None:
     """Format a type hint to a readable string."""
+    import ifcopenshell
+
     if hint is None:
         return None
     if hint is type(None):
         return "None"
+    # ifcopenshell.file params are passed as a file path string
+    if hint is ifcopenshell.file:
+        return "file_path"
     origin = typing.get_origin(hint)
     args = typing.get_args(hint)
 
diff --git a/src/ifcedit/ifcedit/run.py b/src/ifcedit/ifcedit/run.py
index c361715c06..91d8be6774 100644
--- a/src/ifcedit/ifcedit/run.py
+++ b/src/ifcedit/ifcedit/run.py
@@ -28,6 +28,17 @@ import ifcopenshell
 from ifcedit.coerce import coerce_value
 
 
+def _is_file_type(hint) -> bool:
+    """Check if a type hint refers to ifcopenshell.file (or Optional[ifcopenshell.file])."""
+    if hint is ifcopenshell.file:
+        return True
+    origin = typing.get_origin(hint)
+    args = typing.get_args(hint)
+    if origin is typing.Union and ifcopenshell.file in args:
+        return True
+    return False
+
+
 def run_api(
     model: ifcopenshell.file,
     module: str,
@@ -58,12 +69,36 @@ def run_api(
 
     sig = inspect.signature(fn)
     coerced_kwargs = {}
+
+    # Pass 1: coerce ifcopenshell.file-typed params first (e.g. library= in append_asset).
+    # The opened file is then used as the lookup file for entity resolution in pass 2.
+    opened_files: list[ifcopenshell.file] = []
     for name, value_str in raw_kwargs.items():
         if name not in sig.parameters:
             return {"ok": False, "error": f"Unknown parameter '{name}' for {module}.{function}"}
         hint = hints.get(name)
+        if not _is_file_type(hint):
+            continue
         try:
-            coerced_kwargs[name] = coerce_value(value_str, hint, model)
+            coerced = coerce_value(value_str, hint, model)
+            coerced_kwargs[name] = coerced
+            if isinstance(coerced, ifcopenshell.file):
+                opened_files.append(coerced)
+        except (ValueError, TypeError) as e:
+            return {"ok": False, "error": f"Cannot convert parameter '{name}': {e}"}
+
+    # Pass 2: coerce remaining params. Entity instance IDs are resolved from the opened
+    # library file (if any), since you are always appending from another file, never
+    # from the current model.
+    lookup_file = opened_files[0] if opened_files else None
+    for name, value_str in raw_kwargs.items():
+        if name in coerced_kwargs:
+            continue
+        if name not in sig.parameters:
+            return {"ok": False, "error": f"Unknown parameter '{name}' for {module}.{function}"}
+        hint = hints.get(name)
+        try:
+            coerced_kwargs[name] = coerce_value(value_str, hint, model, lookup_file=lookup_file)
         except (ValueError, TypeError) as e:
             return {"ok": False, "error": f"Cannot convert parameter '{name}': {e}"}
 
diff --git a/src/ifcedit/tests/conftest.py b/src/ifcedit/tests/conftest.py
index 941bb90426..017578a343 100644
--- a/src/ifcedit/tests/conftest.py
+++ b/src/ifcedit/tests/conftest.py
@@ -8,6 +8,7 @@ import ifcopenshell.api.root
 import ifcopenshell.api.spatial
 import ifcopenshell.api.unit
 import pytest
+import ifcopenshell.api.material
 
 
 @pytest.fixture
@@ -40,3 +41,23 @@ def model_file(model, tmp_path):
     path = tmp_path / "test.ifc"
     model.write(str(path))
     return str(path)
+
+
+@pytest.fixture
+def library():
+    """Create an IFC4 library with a single IfcWallType asset."""
+    lib = ifcopenshell.api.project.create_file()
+    ifcopenshell.api.owner.settings.get_user = lambda ifc: (ifc.by_type("IfcPersonAndOrganization") or [None])[0]
+    ifcopenshell.api.owner.settings.get_application = lambda ifc: (ifc.by_type("IfcApplication") or [None])[0]
+    ifcopenshell.api.root.create_entity(lib, ifc_class="IfcProject", name="TestLibrary")
+    ifcopenshell.api.unit.assign_unit(lib)
+    ifcopenshell.api.root.create_entity(lib, ifc_class="IfcWallType", name="WAL01")
+    return lib
+
+
+@pytest.fixture
+def library_file(library, tmp_path):
+    """Write the library fixture to a temp file and return the path."""
+    path = tmp_path / "library.ifc"
+    library.write(str(path))
+    return str(path)
diff --git a/src/ifcedit/tests/test_coerce.py b/src/ifcedit/tests/test_coerce.py
index 6028d910cb..620ab139b7 100644
--- a/src/ifcedit/tests/test_coerce.py
+++ b/src/ifcedit/tests/test_coerce.py
@@ -3,6 +3,7 @@ import json
 from typing import Literal, Optional, Union
 
 import ifcopenshell
+import ifcopenshell.api.project
 import pytest
 
 from ifcedit.coerce import coerce_value
@@ -125,6 +126,20 @@ class TestEntityCoercion:
             coerce_value("42", ifcopenshell.entity_instance, None)
 
 
+class TestFileCoercion:
+    def test_opens_file_from_path(self, model_file):
+        result = coerce_value(model_file, ifcopenshell.file)
+        assert isinstance(result, ifcopenshell.file)
+
+    def test_entity_from_lookup_file(self, model_file):
+        lib = ifcopenshell.open(model_file)
+        wall = lib.by_type("IfcWall")[0]
+        empty_model = ifcopenshell.api.project.create_file()
+        result = coerce_value(str(wall.id()), ifcopenshell.entity_instance, empty_model, lookup_file=lib)
+        assert result.id() == wall.id()
+        assert result.is_a("IfcWall")
+
+
 class TestFallback:
     def test_no_type_hint(self):
         assert coerce_value("hello", None) == "hello"
diff --git a/src/ifcedit/tests/test_run.py b/src/ifcedit/tests/test_run.py
index f2d940ee98..620614ff08 100644
--- a/src/ifcedit/tests/test_run.py
+++ b/src/ifcedit/tests/test_run.py
@@ -1,5 +1,7 @@
 # This file was generated with the assistance of an AI coding tool.
+import ifcopenshell
 import ifcopenshell.api.pset
+import ifcopenshell.api.project
 import ifcopenshell.api.root
 
 from ifcedit.run import run_api, serialize_result
@@ -52,6 +54,21 @@ class TestRunApi:
         assert "not found" in result["error"]
 
 
+class TestAppendAsset:
+    def test_append_asset_from_library(self, model, library_file):
+        lib = ifcopenshell.open(library_file)
+        wall_type = lib.by_type("IfcWallType")[0]
+        result = run_api(
+            model,
+            "project",
+            "append_asset",
+            {"library": library_file, "element": str(wall_type.id())},
+        )
+        assert result["ok"] is True
+        assert result["result"]["type"] == "IfcWallType"
+        assert model.by_type("IfcWallType"), "wall type should have been appended to the model"
+
+
 class TestSerializeResult:
     def test_none(self):
         assert serialize_result(None) is None