features/consolidated_tool.feature

@@ -587,6 +587,15 @@ Feature: Consolidated Tool
     When I attempt to attach validation via the coverage service
     Then a coverage NotFoundError should be raised with message containing "not found"
 
+    # --- attach_validation: type discriminator rejects plain tools -------------
+
+
+  Scenario: attach_validation raises ValidationError when a plain tool is passed
+    Given a mock-based tool registry service
+    Given the mock tool repo returns a plain tool entry for get_by_name
+    When I attempt to attach validation via the coverage service
+    Then a coverage ValidationError should be raised with message containing "plain tool"
+
     # --- attach_validation: successful delegation ------------------------------
 
 

features/steps/tool_registry_service_coverage_steps.py

@@ -14,7 +14,7 @@ from behave.runner import Context
 from cleveragents.application.services.tool_registry_service import (
     ToolRegistryService,
 )
-from cleveragents.core.exceptions import DatabaseError, NotFoundError
+from cleveragents.core.exceptions import DatabaseError, NotFoundError, ValidationError
 from cleveragents.infrastructure.database.repositories import (
     DuplicateToolError,
     ToolInUseError,
@@ -146,10 +146,20 @@ def step_repo_returns_none(context: Context) -> None:
 def step_repo_returns_sentinel(context: Context) -> None:
     context.cov_tool_repo._get_by_name_return = {
         "name": "local/some-check",
+        "tool_type": "validation",
         "mode": "required",
     }
 
 
+@given("the mock tool repo returns a plain tool entry for get_by_name")
+def step_repo_returns_plain_tool(context: Context) -> None:
+    context.cov_tool_repo._get_by_name_return = {
+        "name": "local/plain-tool",
+        "tool_type": "tool",
+        "source": "builtin",
+    }
+
+
 # ---------------------------------------------------------------------------
 # When
 # ---------------------------------------------------------------------------
@@ -268,3 +278,16 @@ def step_then_no_error(context: Context) -> None:
     assert context.cov_error is None, (
         f"Expected no error, got {type(context.cov_error).__name__}: {context.cov_error}"
     )
+
+
+@then('a coverage ValidationError should be raised with message containing "{text}"')
+def step_then_validation_error(context: Context, text: str) -> None:
+    assert context.cov_error is not None, (
+        "Expected ValidationError but no error was raised"
+    )
+    assert isinstance(context.cov_error, ValidationError), (
+        f"Expected ValidationError, got {type(context.cov_error).__name__}: {context.cov_error}"
+    )
+    assert text in str(context.cov_error), (
+        f"Expected '{text}' in error message, got '{context.cov_error}'"
+    )

robot/helper_tool_cli.py

@@ -193,6 +193,35 @@ def validation_detach() -> None:
     print("validation-cli-detach-ok")
 
 
+def validation_attach_plain_tool() -> None:
+    """Verify validation attach rejects a plain tool with a non-zero exit code."""
+    from cleveragents.core.exceptions import ValidationError
+
+    svc = MagicMock()
+    svc.attach_validation.side_effect = ValidationError(
+        "'local/plain-tool' is a plain tool, not a validation — "
+        "only entries with tool_type='validation' may be attached as validations."
+    )
+    with patch(
+        "cleveragents.cli.commands.validation._get_tool_registry_service",
+        return_value=svc,
+    ):
+        result = runner.invoke(
+            validation_app,
+            ["attach", "resource/r1", "local/plain-tool"],
+        )
+    # typer.Abort() results in exit code 1
+    assert result.exit_code != 0, (
+        f"Expected non-zero exit code for plain tool, "
+        f"got {result.exit_code}: {result.output}"
+    )
+    output_lower = result.output.lower()
+    assert "plain tool" in output_lower or "validation error" in output_lower, (
+        f"Expected error message about plain tool, got: {result.output}"
+    )
+    print("validation-cli-attach-plain-tool-rejected")
+
+
 _COMMANDS = {
     "tool-add-config": tool_add_config,
     "tool-list": tool_list_all,
@@ -200,6 +229,7 @@ _COMMANDS = {
     "tool-remove": tool_remove_name,
     "validation-add-config": validation_add_config,
     "validation-attach": validation_attach,
+    "validation-attach-plain-tool": validation_attach_plain_tool,
     "validation-detach": validation_detach,
 }
 

robot/tool_cli.robot

@@ -55,3 +55,9 @@ Validation Detach Removes Attachment
     ${result}=    Run Process    ${PYTHON}    ${HELPER}    validation-detach    cwd=${WORKSPACE}
     Should Be Equal As Integers    ${result.rc}    0
     Should Contain    ${result.stdout}    validation-cli-detach-ok
+
+Validation Attach Rejects Plain Tool
+    [Documentation]    Verify that ``validation attach`` rejects a plain tool name with a non-zero exit code and descriptive error message
+    ${result}=    Run Process    ${PYTHON}    ${HELPER}    validation-attach-plain-tool    cwd=${WORKSPACE}
+    Should Be Equal As Integers    ${result.rc}    0
+    Should Contain    ${result.stdout}    validation-cli-attach-plain-tool-rejected

src/cleveragents/application/services/tool_registry_service.py

@@ -9,7 +9,7 @@ from __future__ import annotations
 
 from typing import Any
 
-from cleveragents.core.exceptions import NotFoundError
+from cleveragents.core.exceptions import NotFoundError, ValidationError
 from cleveragents.domain.models.core.tool import Tool
 from cleveragents.infrastructure.database.repositories import (
     ToolRegistryRepository,
@@ -153,6 +153,12 @@ class ToolRegistryService:
         the validation's registered definition — it is not an attach-time
         override.
 
+        The ``tool_type`` discriminator stored in the Tool Registry is enforced
+        here: only entries tagged as ``"validation"`` may be attached.  Passing
+        the name of a plain tool (``tool_type="tool"``) raises a
+        :class:`~cleveragents.core.exceptions.ValidationError` so that the
+        type-safety guarantee described in the specification is upheld.
+
         Args:
             validation_name: Name of the validation tool to attach.
             resource_id: Resource reference string.
@@ -165,6 +171,8 @@ class ToolRegistryService:
 
         Raises:
             NotFoundError: If the validation tool does not exist.
+            ValidationError: If the named entry is a plain tool rather than a
+                validation (``tool_type != "validation"``).
             DatabaseError: On persistence failure.
         """
         # Verify validation exists
@@ -175,6 +183,18 @@ class ToolRegistryService:
                 resource_id=validation_name,
             )
 
+        # Enforce the type discriminator: only "validation" entries are allowed.
+        if isinstance(existing, dict):
+            tool_type = existing.get("tool_type")
+        else:
+            tool_type = getattr(existing, "tool_type", None)
+        if tool_type != "validation":
+            raise ValidationError(
+                f"'{validation_name}' is a plain tool, not a validation — "
+                "only entries with tool_type='validation' may be attached as "
+                "validations. Register a proper validation schema first."
+            )
+
         # Read mode from the validation's registered definition
         if isinstance(existing, dict):
             mode = existing.get("mode", "required")