fix(config): report computed fields as read-only on update (#1454)

PUT /v1/config/{path} answered "does not exist in model" when the
target was a computed field such as eos_device_instruction_entity_ids.
Raise an explicit read-only error instead, so API clients can tell
read-only fields from unknown ones.

Closes #913

CHANGELOG.md

@@ -106,6 +106,9 @@ compatibility changes and a short test procedure. These changes are not yet a ta
 - GENETIC reads its horizon, interval and prediction settings once at the start of a run. A
   configuration change during a run (for example a client adapting the control horizon) no
   longer fails the run with an out-of-bounds error; it applies to the next run.
+- Updating a read-only computed configuration field, e.g. `adapter.homeassistant.eos_solution_entity_ids`
+  via `PUT /v1/config/{path}`, now reports a read-only error instead of claiming the field does
+  not exist ([#913](https://github.com/Akkudoktor-EOS/EOS/issues/913)).
 
 ## 0.3.0 (2026-03-17)
 

src/akkudoktoreos/core/pydantic.py

@@ -569,6 +569,11 @@ class PydanticModelNestedValueMixin:
             raise TypeError(f"Model '{model}' is not of class type.")
 
         if key not in model.model_fields:
+            if key in model.model_computed_fields:
+                raise TypeError(
+                    f"Field '{key}' of model '{model.__name__}' is a read-only computed "
+                    "field and cannot be updated."
+                )
             raise TypeError(f"Field '{key}' does not exist in model '{model.__name__}'.")
 
         field_annotation = model.model_fields[key].annotation

tests/test_config.py

@@ -486,6 +486,18 @@ def test_set_nested_key(path, value, expected, exception, config_eos):
                 f"Expected exception {exception}, but got {type(e)}: {e}"
             )
 
+def test_set_nested_key_read_only_computed_field(config_eos):
+    """Setting a computed field is reported as read-only, not as missing."""
+    path = "adapter/homeassistant/eos_device_instruction_entity_ids"
+    with pytest.raises(TypeError, match="read-only computed field"):
+        config_eos.set_nested_value(path, ["sensor.eos_battery1"])
+
+
+def test_set_nested_key_unknown_field_still_reports_missing(config_eos):
+    """A field that does not exist keeps the original 'does not exist' message."""
+    with pytest.raises(TypeError, match="does not exist in model"):
+        config_eos.set_nested_value("adapter/homeassistant/no_such_field", 1)
+
 
 @pytest.mark.parametrize(
     "path, expected_value, exception",

tests/test_pydantic.py

@@ -3,7 +3,7 @@ from typing import Any, Optional
 import pandas as pd
 import pendulum
 import pytest
-from pydantic import Field, ValidationError
+from pydantic import BaseModel, Field, ValidationError, computed_field
 
 from akkudoktoreos.core.pydantic import (
     PydanticBaseModel,
@@ -199,6 +199,20 @@ class TestPydanticModelNestedValueMixin:
         with pytest.raises(TypeError):
             PydanticModelNestedValueMixin._get_key_types(User, "unknown_field")
 
+    def test_get_key_types_for_computed_field(self):
+        """Test _get_key_types reports a computed field as read-only."""
+
+        class WithComputed(BaseModel):
+            value: int = 1
+
+            @computed_field  # type: ignore[prop-decorator]
+            @property
+            def doubled(self) -> int:
+                return self.value * 2
+
+        with pytest.raises(TypeError, match="read-only computed field"):
+            PydanticModelNestedValueMixin._get_key_types(WithComputed, "doubled")
+
     def test_get_key_types_for_instance_raises(self, user_instance):
         """Test _get_key_types raises an error for an instance."""
         with pytest.raises(TypeError):