diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1088eb3..456a584 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,22 @@ and this project adheres to [Clever Semantic Versioning](https://www.w3.org/subm
 
 ### Added
 
+- **`tool_agent_class` Injection Parameter for `AgentFactory` and `create_executor` (issue #73)** (`agents/factory.py`, `agents/llm.py`, `runtime.py`, `runtime_dispatch.py`, `core/application.py`): Eliminates the monkey-patching workaround required by `cleveragents-webapp` to substitute a platform-controlled `ToolAgent` subclass at runtime.
+
+  `AgentFactory.__init__` now accepts a keyword-only `tool_agent_class: type[ToolAgent] = ToolAgent` argument.  When provided, the supplied subclass is used in place of the module-level `ToolAgent` default everywhere the factory constructs or registers tool agents — specifically, the `"tool"` entry in `self.agent_types` is populated with the supplied class so `create_agent()` instantiates it directly.
+
+  `Executor.__init__` and `create_executor()` accept the same parameter and store it on `self.tool_agent_class`.  All six dispatch paths that construct or dispatch tool agents are updated to honour this attribute: `_execute_tool` uses `executor.tool_agent_class(...)` instead of `ToolAgent(...)`; `_execute_graph` and `_execute_graph_stream` forward `tool_agent_class=executor.tool_agent_class` to `AgentFactory` (so graph nodes with tool-typed agents pick up the subclass); `_execute_llm` and `_execute_llm_stream` forward `tool_agent_class=executor.tool_agent_class` to `AgentFactory` (so the single-LLM actor's internal tool-calling loop uses the subclass); and `_execute_multi_actor` forwards `tool_agent_class=executor.tool_agent_class` to the sub-`Executor` (so every actor inside a multi-actor bundle — tool, graph, or LLM — honours the injected subclass).
+
+  `LLMAgent.__init__` accepts the same keyword-only `tool_agent_class` argument (validated as a `ToolAgent` subclass) and `AgentFactory._create_agent_instance` forwards it when creating `"llm"`-typed agents.  The multi-turn tool-call loop in `LLMAgent._execute_tool_loop` constructs its ephemeral tool executors via `self._tool_agent_class(...)` (covering the regular loop, the budget-exhaustion synthesis round, and the stuck-model synthesis round), so the LLM tool-calling path no longer falls back to the module-level `ToolAgent`.
+
+  `ReactiveCleverAgentsApp` no longer redundantly re-registers the module-level `ToolAgent` (the factory already owns the `"tool"` registration), and the now-unused `ToolAgent` import was removed from `runtime_dispatch.py` (the dispatch path uses `executor.tool_agent_class`).
+
+  Both `AgentFactory`, `Executor`, and `LLMAgent` validate that the supplied class is a subclass of `ToolAgent` at construction time (fail-fast, per `CONTRIBUTING.md §Argument Validation`).
+
+  **Backward-compatibility:** callers that do not pass `tool_agent_class` receive identical behaviour to the previous release — the default is `ToolAgent` itself.
+
+  **Module:** `src/cleveractors/agents/factory.py` (`AgentFactory.__init__`, `_create_agent_instance`), `src/cleveractors/agents/llm.py` (`LLMAgent.__init__`, `_execute_tool_loop`), `src/cleveractors/runtime.py` (`Executor.__init__`, `create_executor`), `src/cleveractors/runtime_dispatch.py` (`_execute_tool`, `_execute_graph`, `_execute_graph_stream`, `_execute_llm`, `_execute_llm_stream`, `_execute_multi_actor`), `src/cleveractors/core/application.py` (`load_configuration`, `_create_agents`).  BDD: scenarios in `features/tool_agent_class_injection.feature`.
+
 - **LLM Agent Token-Budget Awareness and Tool Output Pruning (issue #61, #65)** (`llm.py`): Two complementary mechanisms to prevent context-window exhaustion in the multi-turn tool-call loop, with accurate token tracking for billing.
 
   **Token-budget awareness** (`token_budget_percent` config, default off): tracks actual token consumption from LLM response metadata before each invocation. Emits a warning at 75% budget consumption. When the budget ceiling is exceeded, injects a synthesis prompt, permits one final tool-call round, then forces a text-only response. Token counts from all rounds (including budget-exhaustion synthesis, stuck-model synthesis, and pruning passes) are accumulated for accurate billing.
diff --git a/features/application_coverage_gaps.feature b/features/application_coverage_gaps.feature
index 111be59..7c255a1 100644
--- a/features/application_coverage_gaps.feature
+++ b/features/application_coverage_gaps.feature
@@ -166,11 +166,6 @@ Feature: Application Error Handling, Stream Routing, and Tool Execution
     When start_interactive_session encounters a RuntimeError (apg)
     Then the error should be wrapped in CleverAgentsException with session message (apg)
 
-  Scenario: _create_agents registers built-in agent types
-    Given an app with config and agent_factory (apg)
-    When _create_agents is called (apg)
-    Then LLMAgent and ToolAgent types should be registered in the factory (apg)
-
   Scenario: _sanitize_json_string returns already-valid JSON unchanged
     Given a fresh application gaps test context (apg)
     When _sanitize_json_string is called with a valid JSON string (apg)
diff --git a/features/steps/application_coverage_gaps_steps.py b/features/steps/application_coverage_gaps_steps.py
index 375ade3..844acd9 100644
--- a/features/steps/application_coverage_gaps_steps.py
+++ b/features/steps/application_coverage_gaps_steps.py
@@ -1044,28 +1044,12 @@ def step_apg_assert_session_wrap(context):
 
 
 # ---- _create_agents register built-in types ----
-
-
-@when("_create_agents is called (apg)")
-def step_apg_call_create_agents(context):
-    app = context.apg_app
-    factory = app.agent_factory
-    with (
-        patch.object(factory, "register_agent_type") as reg,
-        patch.object(factory, "get_agent_types", return_value=[]),
-    ):
-        app._create_agents()
-    context.apg_results["registered_calls"] = [
-        c[0][0] for c in reg.call_args_list if c[0]
-    ]
-
-
-@then("LLMAgent and ToolAgent types should be registered in the factory (apg)")
-def step_apg_assert_types_registered(context):
-    calls = context.apg_results.get("registered_calls", [])
-    assert "llm" in calls
-    assert "tool" in calls
-
+# The former "_create_agents registers built-in agent types" scenario and its
+# step definitions were removed: ``_create_agents`` no longer redundantly
+# re-registers the built-in agent types (the factory's ``__init__`` owns that
+# registration, issue #73).  ``_create_agents`` itself is still exercised
+# end-to-end by every scenario that loads a configuration via
+# ``load_configuration``.
 
 # ---- _sanitize_json_string fast path ----
 
diff --git a/features/steps/credential_executor_paths_steps.py b/features/steps/credential_executor_paths_steps.py
index 9409d0a..50e9d62 100644
--- a/features/steps/credential_executor_paths_steps.py
+++ b/features/steps/credential_executor_paths_steps.py
@@ -79,6 +79,8 @@ async def step_execute_multi_actor(context: Any, message: str) -> None:
         credentials: Any,
         limits: Any,
         pricing: Any,
+        tool_agent_class: Any = None,
+        **_extra_kwargs: Any,
     ) -> None:
         context._sub_executor_credentials = copy.deepcopy(credentials)
         # Patch execute on the sub-executor to avoid real LLM calls
@@ -90,7 +92,23 @@ async def step_execute_multi_actor(context: Any, message: str) -> None:
                 nodes=[],
             )
         )
-        original_init(self_exec, config_dict, credentials, limits, pricing)
+        # Forward tool_agent_class (keyword-only on Executor.__init__) so the
+        # sub-Executor honours the parent's injected subclass; this mirrors the
+        # real _execute_multi_actor call site, which forwards the attribute
+        # (issue #73).  When the kwarg is absent, fall back to Executor's own
+        # default (ToolAgent) by omitting it.  Other keyword-only args are
+        # accepted via _extra_kwargs for forward-compatibility.
+        if tool_agent_class is not None:
+            original_init(
+                self_exec,
+                config_dict,
+                credentials,
+                limits,
+                pricing,
+                tool_agent_class=tool_agent_class,
+            )
+        else:
+            original_init(self_exec, config_dict, credentials, limits, pricing)
 
     try:
         with patch.object(Executor, "__init__", capturing_init):
diff --git a/features/steps/runtime_coverage_steps.py b/features/steps/runtime_coverage_steps.py
index 65c5474..64c7ec7 100644
--- a/features/steps/runtime_coverage_steps.py
+++ b/features/steps/runtime_coverage_steps.py
@@ -62,7 +62,6 @@ async def step_execute_actor(context: Any, msg: str) -> None:
 
     with (
         patch("cleveractors.runtime_dispatch.TemplateRenderer") as mock_renderer,
-        patch("cleveractors.runtime_dispatch.ToolAgent") as mock_tool,
         patch("cleveractors.agents.llm.LLMAgent") as mock_llm,
         patch("cleveractors.runtime_dispatch.AgentFactory") as mock_factory,
         patch("cleveractors.runtime_dispatch.PureLangGraph") as mock_pure_graph,
@@ -88,12 +87,6 @@ async def step_execute_actor(context: Any, msg: str) -> None:
 
         mock_llm.return_value = mock_llm_instance
 
-        mock_tool_instance = MagicMock()
-        mock_tool_instance.process_message = AsyncMock(
-            return_value="Mock tool response"
-        )
-        mock_tool.return_value = mock_tool_instance
-
         mock_graph_instance = MagicMock()
         # PureLangGraph.execute() returns a 3-tuple (AC4): (response, state, node_usages)
         mock_graph_instance.execute = AsyncMock(
diff --git a/features/steps/runtime_extended_coverage_steps.py b/features/steps/runtime_extended_coverage_steps.py
index ad2f0fc..91fd0e1 100644
--- a/features/steps/runtime_extended_coverage_steps.py
+++ b/features/steps/runtime_extended_coverage_steps.py
@@ -10,6 +10,7 @@ from behave import given, then, when
 from behave.api.async_step import async_run_until_complete
 from behave.runner import Context
 
+from cleveractors.agents.tool import ToolAgent
 from cleveractors.core.exceptions import ConfigurationError
 from cleveractors.runtime import Executor, create_executor
 
@@ -290,10 +291,6 @@ async def step_rxe_execute(context: Context, message: str) -> None:
     mock_llm_inst.cleanup = AsyncMock()
     mock_llm_inst._last_token_usage = (100, 50)
 
-    mock_tool_inst = MagicMock()
-    mock_tool_inst.process_message = AsyncMock(return_value="Mock tool response")
-    mock_tool_inst.cleanup = AsyncMock()
-
     mock_graph_inst = MagicMock()
     # PureLangGraph.execute() returns a 3-tuple (AC4, issue #14)
     mock_graph_inst.execute = AsyncMock(return_value=("Mock graph response", {}, []))
@@ -309,14 +306,12 @@ async def step_rxe_execute(context: Context, message: str) -> None:
         # and check credentials.
         with (
             patch("cleveractors.agents.llm.LLMAgent") as mock_llm,
-            patch("cleveractors.runtime_dispatch.ToolAgent") as mock_tool,
             patch("cleveractors.runtime_dispatch.PureLangGraph") as mock_pure_graph,
             patch(
                 "cleveractors.langgraph.pure_graph.PureGraphConfig"
             ) as mock_pg_config,
         ):
             mock_llm.return_value = mock_llm_inst
-            mock_tool.return_value = mock_tool_inst
             mock_pure_graph.return_value = mock_graph_inst
             mock_pg_config.return_value = MagicMock()
 
@@ -349,7 +344,15 @@ async def step_rxe_execute(context: Context, message: str) -> None:
 
     with (
         patch("cleveractors.runtime_dispatch.TemplateRenderer") as mock_renderer,
-        patch("cleveractors.runtime_dispatch.ToolAgent") as mock_tool,
+        # executor.tool_agent_class is the real ToolAgent class; patch its
+        # process_message so tool actors return a canned response without
+        # executing actual tools (issue #73: module-level ToolAgent patch no
+        # longer intercepts construction via executor.tool_agent_class).
+        patch.object(
+            ToolAgent,
+            "process_message",
+            AsyncMock(return_value="Mock tool response"),
+        ),
         patch("cleveractors.agents.llm.LLMAgent") as mock_llm,
         patch("cleveractors.runtime_dispatch.AgentFactory") as mock_factory,
         patch("cleveractors.runtime_dispatch.PureLangGraph") as mock_pure_graph,
@@ -358,7 +361,6 @@ async def step_rxe_execute(context: Context, message: str) -> None:
         mock_renderer_inst = MagicMock()
         mock_renderer.return_value = mock_renderer_inst
         mock_llm.return_value = mock_llm_inst
-        mock_tool.return_value = mock_tool_inst
         mock_pure_graph.return_value = mock_graph_inst
         mock_pg_config.return_value = MagicMock()
         mock_factory.return_value = mock_factory_inst
diff --git a/features/steps/tool_agent_class_injection_steps.py b/features/steps/tool_agent_class_injection_steps.py
new file mode 100644
index 0000000..fd97299
--- /dev/null
+++ b/features/steps/tool_agent_class_injection_steps.py
@@ -0,0 +1,720 @@
+"""Step definitions for tool_agent_class injection BDD tests (issue #73).
+
+Tests that AgentFactory and create_executor accept a ``tool_agent_class``
+keyword argument and use it in place of the module-level ``ToolAgent``
+default for all internal tool-agent construction paths.
+"""
+
+from __future__ import annotations
+
+from typing import Any
+from unittest.mock import Mock, patch
+
+from behave import given, then, when  # type: ignore[import-untyped]
+from behave.api.async_step import (
+    async_run_until_complete,  # type: ignore[import-untyped]
+)
+from langchain_core.language_models.chat_models import BaseChatModel
+from langchain_core.messages import AIMessage
+
+from cleveractors.agents.factory import AgentFactory
+from cleveractors.agents.tool import ToolAgent
+from cleveractors.core.exceptions import ConfigurationError
+from cleveractors.runtime import Executor, create_executor
+from cleveractors.templates.renderer import TemplateRenderer
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+
+
+def _make_tool_agent_subclass(name: str = "CustomToolAgent") -> type[ToolAgent]:
+    """Dynamically create a named ToolAgent subclass for test isolation."""
+    return type(name, (ToolAgent,), {})
+
+
+def _make_minimal_factory_config(agent_name: str = "tool_agent") -> dict[str, Any]:
+    """Minimal AgentFactory config with a single tool-typed agent."""
+    return {
+        "agents": {
+            agent_name: {
+                "type": "tool",
+                "config": {"tools": ["echo"]},
+            }
+        }
+    }
+
+
+def _make_valid_executor_config() -> dict[str, Any]:
+    """Minimal Executor config dict for basic validation tests."""
+    return {
+        "type": "llm",
+        "provider": "openai",
+        "model": "gpt-4o-mini",
+        "system_prompt": "You are a helper.",
+    }
+
+
+def _make_valid_tool_executor_config() -> dict[str, Any]:
+    """Minimal Executor config dict for a tool actor."""
+    return {
+        "type": "tool",
+        "name": "test_tool_actor",
+        "tools": ["echo"],
+    }
+
+
+def _make_single_llm_executor_config_with_tools() -> dict[str, Any]:
+    """Minimal Executor config for a single LLM actor that declares tools.
+
+    The ``config.tools`` entry engages ``LLMAgent._execute_tool_loop`` so the
+    injected ``tool_agent_class`` is instantiated when the mock chat model
+    emits a tool call.  This config drives the ``_execute_llm`` dispatch path
+    (issue #73): that path builds an ``AgentFactory`` internally, so the test
+    verifies the executor forwards ``tool_agent_class`` to the factory and on
+    into the LLM agent's tool loop.
+    """
+    return {
+        "type": "llm",
+        "name": "llm_with_tools",
+        "provider": "openai",
+        "model": "gpt-4o-mini",
+        "system_prompt": "You are a helper.",
+        "config": {
+            "tools": [{"name": "echo"}],
+        },
+    }
+
+
+def _make_multi_actor_executor_config_with_tool_sub() -> dict[str, Any]:
+    """Minimal multi-actor bundle config whose default actor is a tool actor.
+
+    Drives the ``_execute_multi_actor`` dispatch path (issue #73): that path
+    builds a sub-:class:`Executor` from the selected actor's config, so the
+    test verifies the parent executor forwards ``tool_agent_class`` to the
+    sub-executor.  The tool sub-actor then runs via ``_execute_tool``, which
+    constructs the agent through ``executor.tool_agent_class(...)``.
+    """
+    return {
+        "type": "multi_actor",
+        "cleveragents": {"default_actor": "tool_sub"},
+        "actors": {
+            "tool_sub": {
+                "type": "tool",
+                "name": "tool_sub",
+                "tools": ["echo"],
+            },
+        },
+    }
+
+
+def _mock_ai_message(
+    text: str,
+    tool_calls: list[dict[str, Any]] | None = None,
+) -> Mock:
+    """Build a mock AIMessage for the LLMAgent tool-loop test.
+
+    Mirrors the response shape used by ``llm_agent_tool_calling_steps``:
+    a ``Mock(spec=AIMessage)`` carrying ``content``, ``tool_calls`` and
+    ``usage_metadata`` so the LLMAgent billing/extraction helpers work.
+    """
+    response = Mock(spec=AIMessage)
+    response.content = text
+    response.tool_calls = tool_calls if tool_calls is not None else None
+    response.usage_metadata = {"input_tokens": 10, "output_tokens": 20}
+    return response
+
+
+# ---------------------------------------------------------------------------
+# Given steps
+# ---------------------------------------------------------------------------
+
+
+@given("a minimal AgentFactory config with a single tool agent")
+def step_minimal_factory_config(context: Any) -> None:
+    context.factory_agent_name = "tool_agent"
+    context.factory_config = _make_minimal_factory_config("tool_agent")
+
+
+@given('a minimal AgentFactory config with a single tool agent named "{agent_name}"')
+def step_minimal_factory_config_named(context: Any, agent_name: str) -> None:
+    context.factory_agent_name = agent_name
+    context.factory_config = _make_minimal_factory_config(agent_name)
+
+
+@given('a custom ToolAgent subclass named "{subclass_name}"')
+def step_custom_tool_agent_subclass(context: Any, subclass_name: str) -> None:
+    context.custom_tool_agent_class = _make_tool_agent_subclass(subclass_name)
+
+
+@given('a custom ToolAgent subclass named "{subclass_name}" that records instantiation')
+def step_custom_tool_agent_subclass_recording(context: Any, subclass_name: str) -> None:
+    context.instantiation_count = 0
+    outer = context
+
+    class RecordingToolAgent(ToolAgent):
+        def __init__(self, *args: Any, **kwargs: Any) -> None:
+            super().__init__(*args, **kwargs)
+            outer.instantiation_count += 1
+
+    RecordingToolAgent.__name__ = subclass_name
+    RecordingToolAgent.__qualname__ = subclass_name
+    context.custom_tool_agent_class = RecordingToolAgent
+
+
+@given("a valid Executor config dict")
+def step_valid_executor_config(context: Any) -> None:
+    context.executor_config = _make_valid_executor_config()
+
+
+@given("a valid tool Executor config dict")
+def step_valid_tool_executor_config(context: Any) -> None:
+    context.executor_config = _make_valid_tool_executor_config()
+
+
+@given("a single-llm Executor config with tools")
+def step_single_llm_executor_config_with_tools(context: Any) -> None:
+    context.executor_config = _make_single_llm_executor_config_with_tools()
+
+
+@given("a multi-actor Executor config with a tool sub-actor")
+def step_multi_actor_executor_config_with_tool_sub(context: Any) -> None:
+    context.executor_config = _make_multi_actor_executor_config_with_tool_sub()
+
+
+@given("an AgentFactory config with a single llm agent that has tools")
+def step_llm_factory_config_with_tools(context: Any) -> None:
+    """AgentFactory config with one LLM agent that declares an ``echo`` tool.
+
+    The LLM agent never makes a real provider call: the When step injects a
+    mock chat model via ``chat_model`` setter, so no API key / LangChain
+    client construction happens.  ``tools`` is what matters — it engages the
+    multi-turn tool-call loop in ``LLMAgent._execute_tool_loop``.
+    """
+    context.factory_agent_name = "llm_with_tools"
+    context.factory_config = {
+        "agents": {
+            "llm_with_tools": {
+                "type": "llm",
+                "config": {
+                    "provider": "openai",
+                    "model": "gpt-4o-mini",
+                    "api_key": "test_key",
+                    "tools": [{"name": "echo"}],
+                },
+            }
+        }
+    }
+
+
+# ---------------------------------------------------------------------------
+# When steps — AgentFactory
+# ---------------------------------------------------------------------------
+
+
+@when("I create an AgentFactory without tool_agent_class")
+def step_create_factory_default(context: Any) -> None:
+    context.factory_error = None
+    try:
+        context.factory = AgentFactory(
+            config=context.factory_config,
+            template_renderer=TemplateRenderer(),
+        )
+    except Exception as exc:  # pylint: disable=broad-exception-caught
+        context.factory_error = exc
+
+
+@when("I create an AgentFactory with that custom tool_agent_class")
+def step_create_factory_custom(context: Any) -> None:
+    context.factory_error = None
+    try:
+        context.factory = AgentFactory(
+            config=context.factory_config,
+            template_renderer=TemplateRenderer(),
+            tool_agent_class=context.custom_tool_agent_class,
+        )
+    except Exception as exc:  # pylint: disable=broad-exception-caught
+        context.factory_error = exc
+
+
+@when("I create an AgentFactory with a non-ToolAgent class as tool_agent_class")
+def step_create_factory_invalid_class(context: Any) -> None:
+    context.factory_error = None
+    try:
+        context.factory = AgentFactory(
+            config=context.factory_config,
+            template_renderer=TemplateRenderer(),
+            tool_agent_class=str,  # type: ignore[arg-type]  # intentionally invalid
+        )
+    except Exception as exc:  # pylint: disable=broad-exception-caught
+        context.factory_error = exc
+
+
+@when('I create the agent named "{agent_name}" from the factory')
+def step_create_agent_from_factory(context: Any, agent_name: str) -> None:
+    context.created_agent_error = None
+    try:
+        context.created_agent = context.factory.create_agent(agent_name)
+    except Exception as exc:  # pylint: disable=broad-exception-caught
+        context.created_agent_error = exc
+
+
+# ---------------------------------------------------------------------------
+# When steps — Executor / create_executor
+# ---------------------------------------------------------------------------
+
+
+@when("I create an Executor without tool_agent_class")
+def step_create_executor_default(context: Any) -> None:
+    context.executor_error = None
+    try:
+        context.test_executor = Executor(
+            config_dict=context.executor_config,
+            credentials=None,
+            limits={},
+            pricing={},
+        )
+    except Exception as exc:  # pylint: disable=broad-exception-caught
+        context.executor_error = exc
+
+
+@when("I create an Executor with that custom tool_agent_class")
+def step_create_executor_custom(context: Any) -> None:
+    context.executor_error = None
+    try:
+        context.test_executor = Executor(
+            config_dict=context.executor_config,
+            credentials=None,
+            limits={},
+            pricing={},
+            tool_agent_class=context.custom_tool_agent_class,
+        )
+    except Exception as exc:  # pylint: disable=broad-exception-caught
+        context.executor_error = exc
+
+
+@when("I create an Executor with a non-ToolAgent class as tool_agent_class")
+def step_create_executor_invalid_class(context: Any) -> None:
+    context.executor_error = None
+    try:
+        context.test_executor = Executor(
+            config_dict=context.executor_config,
+            credentials=None,
+            limits={},
+            pricing={},
+            tool_agent_class=str,  # type: ignore[arg-type]  # intentionally invalid
+        )
+    except Exception as exc:  # pylint: disable=broad-exception-caught
+        context.executor_error = exc
+
+
+@when("I call create_executor without tool_agent_class")
+def step_call_create_executor_no_class(context: Any) -> None:
+    context.executor_error = None
+    try:
+        context.test_executor = create_executor(
+            config_dict=context.executor_config,
+            credentials=None,
+        )
+    except Exception as exc:  # pylint: disable=broad-exception-caught
+        context.executor_error = exc
+
+
+@when("I call create_executor with that custom tool_agent_class")
+def step_call_create_executor_custom(context: Any) -> None:
+    context.executor_error = None
+    try:
+        context.test_executor = create_executor(
+            config_dict=context.executor_config,
+            credentials=None,
+            tool_agent_class=context.custom_tool_agent_class,
+        )
+    except Exception as exc:  # pylint: disable=broad-exception-caught
+        context.executor_error = exc
+
+
+@when("I execute the tool actor using the custom subclass")
+@async_run_until_complete
+async def step_execute_tool_custom_subclass(context: Any) -> None:
+    """Execute a tool actor with a custom subclass and capture instantiation.
+
+    The custom subclass (set up in the recording Given step) increments
+    ``context.instantiation_count`` each time it is constructed.  We patch
+    enough of the tool execution to avoid actual tool invocation while still
+    exercising the constructor call path in ``_execute_tool``.
+    """
+    executor = create_executor(
+        config_dict=context.executor_config,
+        credentials=None,
+        tool_agent_class=context.custom_tool_agent_class,
+    )
+
+    # Patch process_message on the base class so it doesn't actually run tools.
+    # We use a module-level patch on ToolAgent.process_message (the inherited
+    # method) so the custom subclass picks it up without needing to be patched
+    # separately.  The helper accepts ``**_kwargs`` (rather than a parameter
+    # named ``context``) so it never shadows the Behave ``context`` object that
+    # encloses it, while still absorbing the ``context=`` keyword that the real
+    # ``_execute_tool`` and the LLM tool-loop callers pass through.
+    original_process = ToolAgent.process_message
+
+    async def _fake_process(self: Any, message: str, **_kwargs: Any) -> str:
+        return "echo ok"
+
+    ToolAgent.process_message = _fake_process  # type: ignore[method-assign]
+    try:
+        context.execute_result = await executor.execute("echo hello")
+    finally:
+        ToolAgent.process_message = original_process  # type: ignore[method-assign]
+
+
+@when(
+    "I execute the single-llm Executor with a mock chat model "
+    "that returns one tool call then text"
+)
+@async_run_until_complete
+async def step_execute_single_llm_executor(context: Any) -> None:
+    """Execute a single-LLM executor and assert the injected subclass is used.
+
+    Drives the ``_execute_llm`` dispatch path (issue #73).  That path builds an
+    ``AgentFactory`` internally; with the fix it forwards
+    ``tool_agent_class=executor.tool_agent_class`` so the created ``LLMAgent``
+    receives the recording subclass.  We patch ``build_chat_model`` to return a
+    mock chat model that emits one ``echo`` tool call then a plain-text answer,
+    which engages ``LLMAgent._execute_tool_loop`` — the loop instantiates the
+    injected subclass when dispatching the tool call, incrementing
+    ``context.instantiation_count``.  ``ToolAgent.process_message`` is patched
+    so the recording subclass returns a canned string without running real
+    tools.  ``credentials=None`` is safe because ``build_chat_model`` is fully
+    mocked, so the lazy chat-model init never hits a real provider.
+    """
+    executor = create_executor(
+        config_dict=context.executor_config,
+        credentials=None,
+        tool_agent_class=context.custom_tool_agent_class,
+    )
+
+    call_counter = [0]
+
+    async def _mock_ainvoke(messages: Any, **invoke_kwargs: Any) -> Any:
+        call_counter[0] += 1
+        if call_counter[0] == 1:
+            return _mock_ai_message(
+                "Thinking...",
+                tool_calls=[
+                    {
+                        "id": "call_exec_llm_1",
+                        "type": "function",
+                        "function": {
+                            "name": "echo",
+                            "arguments": '{"text": "hello"}',
+                        },
+                    }
+                ],
+            )
+        return _mock_ai_message("Final answer", tool_calls=None)
+
+    mock_model = Mock(spec=BaseChatModel)
+    mock_model.ainvoke = _mock_ainvoke
+    mock_model.temperature = 0.7
+
+    # Patch ToolAgent.process_message so the recording subclass (which inherits
+    # it) returns a canned string without executing real tools.  ``**_kwargs``
+    # absorbs the ``context=`` keyword the LLM tool loop passes through, and
+    # avoids shadowing the Behave ``context`` object enclosing this helper.
+    original_process = ToolAgent.process_message
+
+    async def _fake_process(self: Any, message: str, **_kwargs: Any) -> str:
+        return "echo ok"
+
+    ToolAgent.process_message = _fake_process  # type: ignore[method-assign]
+    try:
+        with patch(
+            "cleveractors.agents.llm.build_chat_model",
+            return_value=mock_model,
+        ):
+            context.execute_result = await executor.execute("Do something")
+    finally:
+        ToolAgent.process_message = original_process  # type: ignore[method-assign]
+
+
+@when("I execute the multi-actor Executor using the custom subclass")
+@async_run_until_complete
+async def step_execute_multi_actor_executor(context: Any) -> None:
+    """Execute a multi-actor bundle and assert the injected subclass is used.
+
+    Drives the ``_execute_multi_actor`` dispatch path (issue #73).  That path
+    builds a sub-:class:`Executor` from the selected actor's config; with the
+    fix it forwards ``tool_agent_class=executor.tool_agent_class`` to the
+    sub-executor.  The bundle's default actor here is a tool actor, so the
+    sub-executor runs ``_execute_tool``, which constructs the agent via
+    ``executor.tool_agent_class(...)`` — the recording subclass — incrementing
+    ``context.instantiation_count``.  ``ToolAgent.process_message`` is patched
+    so the recording subclass returns a canned string without running real
+    tools.
+    """
+    executor = create_executor(
+        config_dict=context.executor_config,
+        credentials=None,
+        tool_agent_class=context.custom_tool_agent_class,
+    )
+
+    # Same process_message patch strategy as the _execute_tool scenario above.
+    original_process = ToolAgent.process_message
+
+    async def _fake_process(self: Any, message: str, **_kwargs: Any) -> str:
+        return "echo ok"
+
+    ToolAgent.process_message = _fake_process  # type: ignore[method-assign]
+    try:
+        context.execute_result = await executor.execute("echo hello")
+    finally:
+        ToolAgent.process_message = original_process  # type: ignore[method-assign]
+
+
+# ---------------------------------------------------------------------------
+# When steps — LLM agent tool loop (issue #73)
+# ---------------------------------------------------------------------------
+
+
+@when(
+    "I run the llm agent tool loop with a mock chat model "
+    "that returns one tool call then text"
+)
+@async_run_until_complete
+async def step_run_llm_tool_loop(context: Any) -> None:
+    """Drive the LLMAgent tool loop with a mock chat model.
+
+    The agent under test was produced by ``AgentFactory(tool_agent_class=...)``
+    so its internal tool-call loop must construct the injected recording
+    subclass when dispatching the ``echo`` tool call.  ``context.created_agent``
+    is the factory-built LLMAgent; we inject a mock chat model that emits one
+    ``echo`` tool call, then a plain-text final answer, and patch
+    ``ToolAgent.process_message`` so the recording subclass returns a canned
+    string without executing real tools.  The scenario asserts via
+    ``context.instantiation_count`` that the subclass was instantiated.
+    """
+    call_counter = [0]
+
+    async def _mock_ainvoke(messages: Any, **invoke_kwargs: Any) -> Any:
+        call_counter[0] += 1
+        if call_counter[0] == 1:
+            return _mock_ai_message(
+                "Thinking...",
+                tool_calls=[
+                    {
+                        "id": "call_inject_1",
+                        "type": "function",
+                        "function": {
+                            "name": "echo",
+                            "arguments": '{"text": "hello"}',
+                        },
+                    }
+                ],
+            )
+        return _mock_ai_message("Final answer", tool_calls=None)
+
+    mock_model = Mock(spec=BaseChatModel)
+    mock_model.ainvoke = _mock_ainvoke
+    mock_model.temperature = 0.7
+    context.created_agent.chat_model = mock_model
+
+    # Patch ToolAgent.process_message so the recording subclass (which inherits
+    # it) returns a canned string without executing real tools.  ``**_kwargs``
+    # absorbs the ``context=`` keyword the LLM tool loop passes through, and
+    # avoids shadowing the Behave ``context`` object enclosing this helper.
+    original_process = ToolAgent.process_message
+
+    async def _fake_process(self: Any, message: str, **_kwargs: Any) -> str:
+        return "echo ok"
+
+    ToolAgent.process_message = _fake_process  # type: ignore[method-assign]
+    try:
+        context.tool_loop_result = await context.created_agent.process_message(
+            "Do something"
+        )
+    finally:
+        ToolAgent.process_message = original_process  # type: ignore[method-assign]
+
+
+@when("I construct an LLMAgent directly with a non-ToolAgent tool_agent_class")
+def step_construct_llm_with_invalid_tool_agent_class(context: Any) -> None:
+    """Construct LLMAgent directly with an invalid tool_agent_class.
+
+    Validation runs before LangChain is touched (and before super().__init__),
+    so this exercises the fail-fast guard without needing LangChain installed.
+    """
+    from cleveractors.agents.llm import LLMAgent
+
+    context.llm_construct_error: Exception | None = None
+    try:
+        LLMAgent(
+            name="bad_ta_agent",
+            config={"provider": "openai", "model": "gpt-4o-mini"},
+            template_renderer=TemplateRenderer(),
+            tool_agent_class=str,  # type: ignore[arg-type]  # intentionally invalid
+        )
+    except Exception as exc:  # pylint: disable=broad-exception-caught
+        context.llm_construct_error = exc
+
+
+# ---------------------------------------------------------------------------
+# Then steps — AgentFactory assertions
+# ---------------------------------------------------------------------------
+
+
+@then('the factory agent_types["tool"] entry should be the default ToolAgent')
+def step_assert_factory_default_tool_agent(context: Any) -> None:
+    assert context.factory_error is None, (
+        f"Expected no error, got: {context.factory_error}"
+    )
+    agent_types = context.factory.agent_types
+    assert "tool" in agent_types, "Expected 'tool' key in agent_types"
+    assert agent_types["tool"] is ToolAgent, (
+        f"Expected ToolAgent, got {agent_types['tool']}"
+    )
+
+
+@then('the factory agent_types["tool"] entry should be the custom subclass')
+def step_assert_factory_custom_tool_agent(context: Any) -> None:
+    assert context.factory_error is None, (
+        f"Expected no error, got: {context.factory_error}"
+    )
+    agent_types = context.factory.agent_types
+    assert "tool" in agent_types, "Expected 'tool' key in agent_types"
+    assert agent_types["tool"] is context.custom_tool_agent_class, (
+        f"Expected custom subclass, got {agent_types['tool']}"
+    )
+
+
+@then("the factory _tool_agent_class attribute should be the custom subclass")
+def step_assert_factory_tool_agent_class_attr(context: Any) -> None:
+    assert context.factory_error is None, (
+        f"Expected no error, got: {context.factory_error}"
+    )
+    assert context.factory._tool_agent_class is context.custom_tool_agent_class, (
+        f"Expected custom subclass on _tool_agent_class, "
+        f"got {context.factory._tool_agent_class}"
+    )
+
+
+@then('factory creation should raise ConfigurationError containing "{text}"')
+def step_assert_factory_config_error(context: Any, text: str) -> None:
+    assert context.factory_error is not None, (
+        "Expected a ConfigurationError, but no exception was raised"
+    )
+    assert isinstance(context.factory_error, ConfigurationError), (
+        f"Expected ConfigurationError, got {type(context.factory_error).__name__}: "
+        f"{context.factory_error}"
+    )
+    assert text in str(context.factory_error), (
+        f"Expected error message to contain {text!r}, got: {context.factory_error}"
+    )
+
+
+@then("the created agent should be an instance of the custom subclass")
+def step_assert_created_agent_custom_class(context: Any) -> None:
+    assert context.created_agent_error is None, (
+        f"Expected no error creating agent, got: {context.created_agent_error}"
+    )
+    assert isinstance(context.created_agent, context.custom_tool_agent_class), (
+        f"Expected instance of custom subclass, got {type(context.created_agent)}"
+    )
+
+
+@then("the created agent should be an instance of ToolAgent")
+def step_assert_created_agent_tool_agent(context: Any) -> None:
+    assert context.created_agent_error is None, (
+        f"Expected no error creating agent, got: {context.created_agent_error}"
+    )
+    assert isinstance(context.created_agent, ToolAgent), (
+        f"Expected instance of ToolAgent, got {type(context.created_agent)}"
+    )
+
+
+# ---------------------------------------------------------------------------
+# Then steps — Executor assertions
+# ---------------------------------------------------------------------------
+
+
+@then("the executor tool_agent_class attribute should be the default ToolAgent")
+def step_assert_executor_default_tool_agent(context: Any) -> None:
+    assert context.executor_error is None, (
+        f"Expected no error, got: {context.executor_error}"
+    )
+    assert context.test_executor.tool_agent_class is ToolAgent, (
+        f"Expected ToolAgent, got {context.test_executor.tool_agent_class}"
+    )
+
+
+@then("the executor tool_agent_class attribute should be the custom subclass")
+def step_assert_executor_custom_tool_agent(context: Any) -> None:
+    assert context.executor_error is None, (
+        f"Expected no error, got: {context.executor_error}"
+    )
+    assert context.test_executor.tool_agent_class is context.custom_tool_agent_class, (
+        f"Expected custom subclass, got {context.test_executor.tool_agent_class}"
+    )
+
+
+@then('executor creation should raise ConfigurationError containing "{text}"')
+def step_assert_executor_config_error(context: Any, text: str) -> None:
+    assert context.executor_error is not None, (
+        "Expected a ConfigurationError, but no exception was raised"
+    )
+    assert isinstance(context.executor_error, ConfigurationError), (
+        f"Expected ConfigurationError, got {type(context.executor_error).__name__}: "
+        f"{context.executor_error}"
+    )
+    assert text in str(context.executor_error), (
+        f"Expected error message to contain {text!r}, got: {context.executor_error}"
+    )
+
+
+@then("the returned executor tool_agent_class should be the default ToolAgent")
+def step_assert_returned_executor_default(context: Any) -> None:
+    assert context.executor_error is None, (
+        f"Expected no error, got: {context.executor_error}"
+    )
+    assert context.test_executor.tool_agent_class is ToolAgent, (
+        f"Expected ToolAgent, got {context.test_executor.tool_agent_class}"
+    )
+
+
+@then("the returned executor tool_agent_class should be the custom subclass")
+def step_assert_returned_executor_custom(context: Any) -> None:
+    assert context.executor_error is None, (
+        f"Expected no error, got: {context.executor_error}"
+    )
+    assert context.test_executor.tool_agent_class is context.custom_tool_agent_class, (
+        f"Expected custom subclass, got {context.test_executor.tool_agent_class}"
+    )
+
+
+# ---------------------------------------------------------------------------
+# Then steps — _execute_tool dispatch path
+# ---------------------------------------------------------------------------
+
+
+@then("the custom subclass should have been instantiated for tool execution")
+def step_assert_custom_subclass_instantiated(context: Any) -> None:
+    assert context.instantiation_count > 0, (
+        "Expected the custom ToolAgent subclass to be instantiated at least once "
+        f"during tool execution, but instantiation_count={context.instantiation_count}"
+    )
+
+
+@then('LLMAgent construction should raise ConfigurationError containing "{text}"')
+def step_assert_llm_construct_config_error(context: Any, text: str) -> None:
+    assert context.llm_construct_error is not None, (
+        "Expected a ConfigurationError, but no exception was raised"
+    )
+    assert isinstance(context.llm_construct_error, ConfigurationError), (
+        f"Expected ConfigurationError, got "
+        f"{type(context.llm_construct_error).__name__}: "
+        f"{context.llm_construct_error}"
+    )
+    assert text in str(context.llm_construct_error), (
+        f"Expected error message to contain {text!r}, got: "
+        f"{context.llm_construct_error}"
+    )
diff --git a/features/tool_agent_class_injection.feature b/features/tool_agent_class_injection.feature
new file mode 100644
index 0000000..9842217
--- /dev/null
+++ b/features/tool_agent_class_injection.feature
@@ -0,0 +1,118 @@
+Feature: tool_agent_class injection in AgentFactory and create_executor
+  As a platform developer consuming cleveractors-core
+  I want to supply a custom ToolAgent subclass to AgentFactory and create_executor
+  So that I can extend tool agent behaviour without monkey-patching module globals
+
+  # ── AgentFactory ────────────────────────────────────────────────────────────
+
+  Scenario: AgentFactory defaults to ToolAgent when tool_agent_class is omitted
+    Given a minimal AgentFactory config with a single tool agent
+    When I create an AgentFactory without tool_agent_class
+    Then the factory agent_types["tool"] entry should be the default ToolAgent
+
+  Scenario: AgentFactory uses custom subclass when tool_agent_class is provided
+    Given a minimal AgentFactory config with a single tool agent
+    And a custom ToolAgent subclass named "CustomToolAgent"
+    When I create an AgentFactory with that custom tool_agent_class
+    Then the factory agent_types["tool"] entry should be the custom subclass
+
+  Scenario: AgentFactory stores custom subclass on _tool_agent_class attribute
+    Given a minimal AgentFactory config with a single tool agent
+    And a custom ToolAgent subclass named "CustomToolAgent"
+    When I create an AgentFactory with that custom tool_agent_class
+    Then the factory _tool_agent_class attribute should be the custom subclass
+
+  Scenario: AgentFactory rejects non-ToolAgent class as tool_agent_class
+    Given a minimal AgentFactory config with a single tool agent
+    When I create an AgentFactory with a non-ToolAgent class as tool_agent_class
+    Then factory creation should raise ConfigurationError containing "subclass of ToolAgent"
+
+  Scenario: AgentFactory creates tool agent using the custom subclass
+    Given a minimal AgentFactory config with a single tool agent named "my_tool"
+    And a custom ToolAgent subclass named "CustomToolAgent"
+    When I create an AgentFactory with that custom tool_agent_class
+    And I create the agent named "my_tool" from the factory
+    Then the created agent should be an instance of the custom subclass
+
+  Scenario: AgentFactory default behaviour is unchanged (no regression)
+    Given a minimal AgentFactory config with a single tool agent named "default_tool"
+    When I create an AgentFactory without tool_agent_class
+    And I create the agent named "default_tool" from the factory
+    Then the created agent should be an instance of ToolAgent
+
+  # ── Executor and create_executor ────────────────────────────────────────────
+
+  Scenario: Executor defaults to ToolAgent when tool_agent_class is omitted
+    Given a valid Executor config dict
+    When I create an Executor without tool_agent_class
+    Then the executor tool_agent_class attribute should be the default ToolAgent
+
+  Scenario: Executor stores custom subclass on tool_agent_class attribute
+    Given a valid Executor config dict
+    And a custom ToolAgent subclass named "CustomToolAgent"
+    When I create an Executor with that custom tool_agent_class
+    Then the executor tool_agent_class attribute should be the custom subclass
+
+  Scenario: Executor rejects non-ToolAgent class as tool_agent_class
+    Given a valid Executor config dict
+    When I create an Executor with a non-ToolAgent class as tool_agent_class
+    Then executor creation should raise ConfigurationError containing "subclass of ToolAgent"
+
+  Scenario: create_executor defaults to ToolAgent when tool_agent_class is omitted
+    Given a valid Executor config dict
+    When I call create_executor without tool_agent_class
+    Then the returned executor tool_agent_class should be the default ToolAgent
+
+  Scenario: create_executor forwards custom subclass to Executor
+    Given a valid Executor config dict
+    And a custom ToolAgent subclass named "CustomToolAgent"
+    When I call create_executor with that custom tool_agent_class
+    Then the returned executor tool_agent_class should be the custom subclass
+
+  # ── _execute_tool dispatch path ──────────────────────────────────────────────
+
+  Scenario: _execute_tool uses custom subclass when provided via Executor
+    Given a valid tool Executor config dict
+    And a custom ToolAgent subclass named "CustomToolAgent" that records instantiation
+    When I execute the tool actor using the custom subclass
+    Then the custom subclass should have been instantiated for tool execution
+
+  # ── _execute_llm dispatch path (issue #73: AgentFactory forwarding) ─────────
+
+  Scenario: _execute_llm forwards tool_agent_class so the LLM tool loop uses the custom subclass
+    Given a single-llm Executor config with tools
+    And a custom ToolAgent subclass named "RecordingToolAgent" that records instantiation
+    When I execute the single-llm Executor with a mock chat model that returns one tool call then text
+    Then the custom subclass should have been instantiated for tool execution
+
+  # ── _execute_multi_actor dispatch path (issue #73: sub-Executor forwarding) ──
+
+  Scenario: _execute_multi_actor forwards tool_agent_class to the sub-Executor
+    Given a multi-actor Executor config with a tool sub-actor
+    And a custom ToolAgent subclass named "RecordingToolAgent" that records instantiation
+    When I execute the multi-actor Executor using the custom subclass
+    Then the custom subclass should have been instantiated for tool execution
+
+  # ── LLM agent tool loop (issue #73: ephemeral tool executors) ───────────────
+
+  Scenario: LLMAgent tool loop uses the injected tool_agent_class subclass
+    Given an AgentFactory config with a single llm agent that has tools
+    And a custom ToolAgent subclass named "RecordingToolAgent" that records instantiation
+    When I create an AgentFactory with that custom tool_agent_class
+    And I create the agent named "llm_with_tools" from the factory
+    And I run the llm agent tool loop with a mock chat model that returns one tool call then text
+    Then the custom subclass should have been instantiated for tool execution
+
+  Scenario: LLMAgent rejects a non-ToolAgent tool_agent_class at construction
+    Given a custom ToolAgent subclass named "CustomToolAgent"
+    When I construct an LLMAgent directly with a non-ToolAgent tool_agent_class
+    Then LLMAgent construction should raise ConfigurationError containing "subclass of ToolAgent"
+
+  # ── isinstance compatibility ─────────────────────────────────────────────────
+
+  Scenario: Factory-created custom tool agent is an instance of ToolAgent (LSP)
+    Given a minimal AgentFactory config with a single tool agent named "lsp_tool"
+    And a custom ToolAgent subclass named "CustomToolAgent"
+    When I create an AgentFactory with that custom tool_agent_class
+    And I create the agent named "lsp_tool" from the factory
+    Then the created agent should be an instance of ToolAgent
diff --git a/src/cleveractors/agents/factory.py b/src/cleveractors/agents/factory.py
index 7bc06d2..ea3aea8 100644
--- a/src/cleveractors/agents/factory.py
+++ b/src/cleveractors/agents/factory.py
@@ -39,6 +39,12 @@ class AgentFactory:
             dict keyed by provider name (ADR-2026).  When provided, credential
             resolution is delegated to each ``LLMAgent`` via this dict instead
             of relying on environment variables.
+        _tool_agent_class (type[ToolAgent]): The concrete ``ToolAgent``
+            subclass to use for ``"tool"``-typed agents.  Defaults to
+            :class:`~cleveractors.agents.tool.ToolAgent`.  Callers that need
+            to substitute a custom subclass (e.g. a platform-aware subclass
+            with native async handlers) supply it via the ``tool_agent_class``
+            constructor argument rather than monkey-patching module globals.
 
     .. note::
 
@@ -62,6 +68,8 @@ class AgentFactory:
         stream_router: Any | None = None,
         langgraph_bridge: Any | None = None,
         credentials: dict[str, dict[str, str]] | None = None,
+        *,
+        tool_agent_class: type[ToolAgent] = ToolAgent,
     ) -> None:
         """
         Initialize the AgentFactory.
@@ -81,6 +89,17 @@ class AgentFactory:
                 are not consulted.  When ``None``, agents fall back to
                 ``config["api_key"]`` or environment variables (standalone /
                 CLI mode).
+            tool_agent_class: Optional ``ToolAgent`` subclass to use in
+                place of the default :class:`~cleveractors.agents.tool.ToolAgent`.
+                Must be a subclass of ``ToolAgent``.  When provided, every
+                internal factory code path that constructs or registers a
+                ``ToolAgent`` uses this class instead of the module-level
+                default, removing the need for monkey-patching (issue #73).
+
+        Raises:
+            ConfigurationError: If ``config`` is not a dict, ``template_renderer``
+                is not a :class:`~cleveractors.templates.renderer.TemplateRenderer`,
+                or ``tool_agent_class`` is not a subclass of ``ToolAgent``.
         """
         # Argument validation (CONTRIBUTING.md §Argument Validation)
         if not isinstance(config, dict):
@@ -92,11 +111,20 @@ class AgentFactory:
                 f"template_renderer must be a TemplateRenderer, "
                 f"got {type(template_renderer).__name__}"
             )
+        if not (
+            isinstance(tool_agent_class, type)
+            and issubclass(tool_agent_class, ToolAgent)
+        ):
+            raise ConfigurationError(
+                f"tool_agent_class must be a subclass of ToolAgent, "
+                f"got {tool_agent_class!r}"
+            )
+        self._tool_agent_class: type[ToolAgent] = tool_agent_class
         self.credentials = validate_credentials_structure(credentials)
 
-        self.agent_types = {
+        self.agent_types: dict[str, type[Agent]] = {
             "llm": LLMAgent,
-            "tool": ToolAgent,
+            "tool": self._tool_agent_class,
         }
         self.template_renderer = template_renderer
         self.config = config
@@ -271,6 +299,14 @@ class AgentFactory:
                 "config": final_config,
                 "template_renderer": self.template_renderer,
             }
+            # LLMAgent owns the multi-turn tool-call loop and constructs
+            # ephemeral ToolAgent instances internally.  Forward the injected
+            # tool_agent_class so the LLM tool-calling path honours a custom
+            # subclass (issue #73); without this the loop would fall back to
+            # the module-level ToolAgent and the monkey-patch could not be
+            # removed for the LLM path.
+            if agent_type == "llm":
+                kwargs["tool_agent_class"] = self._tool_agent_class
             if agent_type == "llm" and self.credentials is not None:
                 provider = agent_config.get("provider", "openai")
                 if not isinstance(provider, str):
diff --git a/src/cleveractors/agents/llm.py b/src/cleveractors/agents/llm.py
index d0fbd5c..f6fc6c2 100644
--- a/src/cleveractors/agents/llm.py
+++ b/src/cleveractors/agents/llm.py
@@ -40,6 +40,7 @@ from cleveractors.agents.llm_client import build_chat_model
 from cleveractors.agents.llm_imports import populate_langchain_globals
 from cleveractors.agents.llm_tools import normalize_tool_entry as _normalize_tool_entry
 from cleveractors.agents.retry import _get_provider_url, call_with_retry
+from cleveractors.agents.tool import ToolAgent
 from cleveractors.core.exceptions import (
     AgentCreationError,
     ConfigurationError,
@@ -208,6 +209,8 @@ class LLMAgent(AgentWithMemory):
         config: dict[str, Any],
         template_renderer: TemplateRenderer,
         credentials: dict[str, str] | None = None,
+        *,
+        tool_agent_class: type[ToolAgent] = ToolAgent,
     ) -> None:
         """
         Initialize a reactive LLM agent using LangChain.
@@ -225,6 +228,13 @@ class LLMAgent(AgentWithMemory):
                 is required for non-native providers, optional for native ones).
                 When *not* supplied, the agent falls back to ``config["api_key"]``
                 or environment variables (standalone / CLI mode).
+            tool_agent_class: Optional ``ToolAgent`` subclass to use when the
+                multi-turn tool-call loop constructs ephemeral tool executors.
+                Must be a subclass of :class:`~cleveractors.agents.tool.ToolAgent`.
+                Defaults to ``ToolAgent`` itself, preserving pre-existing
+                behaviour.  Supplying a subclass here lets platform consumers
+                override tool agent behaviour for the LLM tool-calling path
+                without monkey-patching module globals (issue #73).
 
         Raises:
             AgentCreationError: If LangChain dependencies are not available.
@@ -261,6 +271,20 @@ class LLMAgent(AgentWithMemory):
         else:
             self._credentials = None
 
+        # tool_agent_class validation (CONTRIBUTING.md §Argument Validation).
+        # Fail fast so an invalid subclass is rejected at construction time
+        # rather than surfacing mid-tool-loop.  This mirrors the validation
+        # performed by AgentFactory and Executor (issue #73).
+        if not (
+            isinstance(tool_agent_class, type)
+            and issubclass(tool_agent_class, ToolAgent)
+        ):
+            raise ConfigurationError(
+                f"tool_agent_class must be a subclass of ToolAgent, "
+                f"got {tool_agent_class!r}"
+            )
+        self._tool_agent_class: type[ToolAgent] = tool_agent_class
+
         super().__init__(name, config, template_renderer)
 
         # Lazy import LangChain dependencies
@@ -905,10 +929,6 @@ class LLMAgent(AgentWithMemory):
                                 _bq_output_prune = args.pop("output_prune", None)
                                 _bq_prune_ctx = args.pop("output_prune_context", None)
                                 try:
-                                    from cleveractors.agents.tool import (
-                                        ToolAgent as _TA,
-                                    )
-
                                     parent_unsafe = self.config.get(
                                         "unsafe_mode", False
                                     )
@@ -923,7 +943,7 @@ class LLMAgent(AgentWithMemory):
                                         ),
                                         "timeout": self.config.get("timeout", 1),
                                     }
-                                    t_agent = _TA(
+                                    t_agent = self._tool_agent_class(
                                         name=f"_tc_synth_budget_{call_id}",
                                         config=tool_cfg,
                                         template_renderer=self.template_renderer,
@@ -1063,8 +1083,6 @@ class LLMAgent(AgentWithMemory):
                     _output_prune = args_m.pop("output_prune", None)
                     _prune_context = args_m.pop("output_prune_context", None)
                     try:
-                        from cleveractors.agents.tool import ToolAgent as _TA
-
                         parent_unsafe = self.config.get("unsafe_mode", False)
                         tool_config: dict[str, Any] = {
                             "tools": [{"name": tool_name}],
@@ -1083,7 +1101,7 @@ class LLMAgent(AgentWithMemory):
                             )
                             continue
 
-                        agent = _TA(
+                        agent = self._tool_agent_class(
                             name=f"_tc_{call_id}",
                             config=tool_config,
                             template_renderer=self.template_renderer,
@@ -1230,10 +1248,6 @@ class LLMAgent(AgentWithMemory):
                         elif isinstance(arguments_raw, dict):
                             args_s = arguments_raw
                         try:
-                            from cleveractors.agents.tool import (
-                                ToolAgent as _TA,
-                            )
-
                             parent_unsafe = self.config.get("unsafe_mode", False)
                             tool_config_s: dict[str, Any] = {
                                 "tools": [{"name": tool_name}],
@@ -1242,7 +1256,7 @@ class LLMAgent(AgentWithMemory):
                                 "exec_python": self.config.get("exec_python", False),
                                 "timeout": self.config.get("timeout", 1),
                             }
-                            agent_s = _TA(
+                            agent_s = self._tool_agent_class(
                                 name=f"_tc_synth_{call_id}",
                                 config=tool_config_s,
                                 template_renderer=self.template_renderer,
diff --git a/src/cleveractors/core/application.py b/src/cleveractors/core/application.py
index d885bee..9f30760 100644
--- a/src/cleveractors/core/application.py
+++ b/src/cleveractors/core/application.py
@@ -12,7 +12,7 @@ import logging
 import re
 import sys
 from pathlib import Path
-from typing import Any, List, Optional, Type, Union
+from typing import Any, List, Optional, Union
 
 from rx.core import Observer  # type: ignore[attr-defined]
 from rx.scheduler.eventloop import AsyncIOScheduler  # type: ignore[attr-defined]
@@ -20,7 +20,6 @@ from rx.scheduler.eventloop import AsyncIOScheduler  # type: ignore[attr-defined
 from cleveractors.agents.base import Agent
 from cleveractors.agents.factory import AgentFactory
 from cleveractors.agents.llm import LLMAgent
-from cleveractors.agents.tool import ToolAgent
 from cleveractors.context_manager import ContextManager
 from cleveractors.core.exceptions import (
     AgentCreationError,
@@ -227,9 +226,15 @@ class ReactiveCleverAgentsApp:  # pylint: disable=too-many-instance-attributes
                 langgraph_bridge=self.langgraph_bridge,
             )
 
-            # Register built-in agent types
+            # Register built-in agent types.
+            # ``AgentFactory.__init__`` already registers ``"llm"`` -> ``LLMAgent``
+            # and ``"tool"`` -> its ``tool_agent_class`` (defaulting to
+            # ``ToolAgent``).  The ``"llm"`` registration below is retained as an
+            # explicit, defensive no-op; the ``"tool"`` registration is intentionally
+            # omitted so this site no longer hardcodes the module-level ``ToolAgent``
+            # symbol (issue #73 audit).  Consumers needing a custom tool subclass use
+            # ``create_executor(tool_agent_class=...)`` directly.
             self.agent_factory.register_agent_type("llm", LLMAgent)
-            self.agent_factory.register_agent_type("tool", ToolAgent)
 
             # Validate agent configuration early to catch errors at load time
             self.agent_factory.validate_configuration()
@@ -927,15 +932,10 @@ class ReactiveCleverAgentsApp:  # pylint: disable=too-many-instance-attributes
         if not self.agent_factory or not self.config:
             raise AgentCreationError("Agent factory or configuration not initialized")
 
-        # Register built-in agent types
-        registered_types = self.agent_factory.get_agent_types()
-        type_map: dict[str, Type[Agent]] = {
-            "llm": LLMAgent,
-            "tool": ToolAgent,
-        }
-        for type_name, agent_class in type_map.items():
-            if type_name not in registered_types:
-                self.agent_factory.register_agent_type(type_name, agent_class)
+        # Built-in agent types ("llm" and "tool") are registered by
+        # ``AgentFactory.__init__``; the redundant re-registration that used to
+        # live here was dead code (the "already registered" guard never fired)
+        # and hardcoded the module-level ``ToolAgent`` symbol (issue #73 audit).
 
         # Create agents
         for agent_name, agent_config in self.config.agents.items():
diff --git a/src/cleveractors/runtime.py b/src/cleveractors/runtime.py
index c75d957..50ae235 100644
--- a/src/cleveractors/runtime.py
+++ b/src/cleveractors/runtime.py
@@ -16,6 +16,7 @@ from __future__ import annotations
 from collections.abc import AsyncGenerator
 from typing import Any
 
+from cleveractors.agents.tool import ToolAgent
 from cleveractors.core.exceptions import ConfigurationError
 from cleveractors.result import ActorResult, NodeUsage
 from cleveractors.runtime_dispatch import (
@@ -47,6 +48,14 @@ class Executor:
 
     Constructed via :func:`create_executor`.  Credentials are per-request;
     the router should construct a new executor per request (ADR-2024).
+
+    Attributes:
+        tool_agent_class (type[ToolAgent]): The concrete ``ToolAgent``
+            subclass used by all dispatch paths that need to construct
+            a ``ToolAgent`` (or register one in ``AgentFactory``).
+            Defaults to :class:`~cleveractors.agents.tool.ToolAgent`.
+            Supply a subclass to override tool agent behaviour at runtime
+            without monkey-patching (issue #73).
     """
 
     def __init__(
@@ -55,6 +64,8 @@ class Executor:
         credentials: dict[str, Any] | None,
         limits: dict[str, Any],
         pricing: dict[str, Any],
+        *,
+        tool_agent_class: type[ToolAgent] = ToolAgent,
     ):
         if not isinstance(config_dict, dict):
             raise ConfigurationError("config_dict must be a dict")
@@ -64,10 +75,19 @@ class Executor:
             raise ConfigurationError("limits must be a dict")
         if not isinstance(pricing, dict):
             raise ConfigurationError("pricing must be a dict")
+        if not (
+            isinstance(tool_agent_class, type)
+            and issubclass(tool_agent_class, ToolAgent)
+        ):
+            raise ConfigurationError(
+                f"tool_agent_class must be a subclass of ToolAgent, "
+                f"got {tool_agent_class!r}"
+            )
         self.config = config_dict
         self.credentials = credentials
         self.limits = limits
         self.pricing = pricing
+        self.tool_agent_class: type[ToolAgent] = tool_agent_class
         # Populated by execute_stream() after the async iterator is exhausted.
         # Remains None until the stream completes (AC4, issue #16).
         self.last_result: ActorResult | None = None
@@ -231,6 +251,8 @@ def create_executor(
     credentials: dict[str, Any] | None,
     limits: dict[str, Any] | None = None,
     pricing: dict[str, Any] | None = None,
+    *,
+    tool_agent_class: type[ToolAgent] = ToolAgent,
 ) -> Executor:
     """Construct an :class:`Executor` for the supplied actor configuration.
 
@@ -241,6 +263,12 @@ def create_executor(
         limits: Optional execution limits
             (max_depth, max_model_calls, max_tool_calls, timeout_ms, max_cost_usd).
         pricing: Optional pricing table for cost enforcement.
+        tool_agent_class: Optional ``ToolAgent`` subclass to use in place of
+            the default :class:`~cleveractors.agents.tool.ToolAgent`.  Must be
+            a subclass of ``ToolAgent``.  When provided, every internal dispatch
+            path that constructs or registers a ``ToolAgent`` uses this class
+            instead of the module-level default, removing the need for
+            monkey-patching (issue #73).
 
     Returns:
         An :class:`Executor` instance.  Call ``await executor.execute(message)``
@@ -251,4 +279,5 @@ def create_executor(
         credentials=credentials,
         limits=limits or {},
         pricing=pricing or {},
+        tool_agent_class=tool_agent_class,
     )
diff --git a/src/cleveractors/runtime_dispatch.py b/src/cleveractors/runtime_dispatch.py
index 8fc8db7..030f5e4 100644
--- a/src/cleveractors/runtime_dispatch.py
+++ b/src/cleveractors/runtime_dispatch.py
@@ -33,7 +33,6 @@ from cleveractors.agents.llm import (
     LLMAgent,
     last_token_usage_var,
 )
-from cleveractors.agents.tool import ToolAgent
 from cleveractors.core.exceptions import (
     AgentCreationError,
     ConfigurationError,
@@ -140,6 +139,7 @@ async def _execute_llm(
         config=factory_cfg,
         credentials=executor.credentials,
         template_renderer=renderer,
+        tool_agent_class=executor.tool_agent_class,
     )
 
     # Build context dict forwarding conversation history for multi-turn support.
@@ -344,6 +344,7 @@ async def _execute_graph(
         config=factory_config,
         credentials=executor.credentials,
         template_renderer=renderer,
+        tool_agent_class=executor.tool_agent_class,
     )
 
     agents: dict[str, Any] = {}
@@ -471,20 +472,25 @@ async def _execute_graph(
 async def _execute_tool(executor: Executor, message: str) -> ActorResult:
     """Execute a single tool actor.
 
-    Constructs a :class:`ToolAgent` from the actor config and invokes
+    Constructs a :class:`~cleveractors.agents.tool.ToolAgent` (via
+    ``executor.tool_agent_class``) from the actor config and invokes
     ``process_message``.  ``ConfigurationError``, ``AgentCreationError``
     and ``ExecutionError`` are propagated directly; all other exceptions
     are wrapped in ``ExecutionError("Tool execution failed: ...")``.
 
-    ToolAgent is constructed directly because tool agents do not require
-    credential injection; AgentFactory is unnecessary for this path.
+    The tool agent is constructed directly via ``executor.tool_agent_class``
+    because tool agents do not require credential injection; AgentFactory is
+    unnecessary for this path.
     """
     config_block: dict[str, Any] = executor.config.get("config", {})
     tools: list[Any] = executor.config.get("tools", config_block.get("tools", []))
 
     agent_config: dict[str, Any] = {"tools": tools}
     renderer = TemplateRenderer()
-    agent = ToolAgent(
+    # Use executor.tool_agent_class so callers that supply a custom subclass
+    # via create_executor(tool_agent_class=...) have it honoured here too
+    # (issue #73).
+    agent = executor.tool_agent_class(
         name=executor.config.get("name", "tool"),
         config=agent_config,
         template_renderer=renderer,
@@ -577,6 +583,7 @@ async def _execute_multi_actor(
         credentials=executor.credentials,
         limits=executor.limits,
         pricing=executor.pricing,
+        tool_agent_class=executor.tool_agent_class,
     )
     result = await sub_executor.execute(message, messages=messages, state=state)
 
@@ -793,6 +800,7 @@ async def _execute_llm_stream(
         config=factory_cfg,
         credentials=executor.credentials,
         template_renderer=renderer,
+        tool_agent_class=executor.tool_agent_class,
     )
 
     llm_context: dict[str, Any] | None = None
@@ -1215,6 +1223,7 @@ async def _execute_graph_stream(
         config=factory_config,
         credentials=executor.credentials,
         template_renderer=renderer,
+        tool_agent_class=executor.tool_agent_class,
     )
 
     agents: dict[str, Any] = {}