diff --git a/features/providers/test_registry_thread_safety.feature b/features/providers/test_registry_thread_safety.feature
new file mode 100644
index 000000000..6e58f82eb
--- /dev/null
+++ b/features/providers/test_registry_thread_safety.feature
@@ -0,0 +1,20 @@
+@tdd_issue @tdd_issue_10409
+Feature: TDD Issue #10409 — Non-thread-safe singleton in get_provider_registry()
+  The function get_provider_registry() in cleveragents.providers.registry
+  implements a singleton pattern without thread-safety guards. Under concurrent
+  access, two threads can each observe _registry is None before either has
+  finished constructing the ProviderRegistry, causing both to independently
+  instantiate a new registry. This violates the singleton contract and can lead
+  to inconsistent provider state across the application.
+
+  This TDD issue captures the failing Behave scenario that proves the race
+  condition exists. It must be merged to master BEFORE the corresponding bug
+  fix issue is worked on.
+
+  See CONTRIBUTING.md > Bug Fix Workflow > TDD Issue Test Tags.
+
+  Scenario: Concurrent calls to get_provider_registry return the same instance
+    Given the global provider registry has been reset
+    When two threads call get_provider_registry() simultaneously
+    Then both threads should receive the identical registry instance
+    And only one ProviderRegistry should have been constructed
diff --git a/features/steps/registry_thread_safety_steps.py b/features/steps/registry_thread_safety_steps.py
new file mode 100644
index 000000000..943abcfcc
--- /dev/null
+++ b/features/steps/registry_thread_safety_steps.py
@@ -0,0 +1,173 @@
+"""Step definitions for TDD Issue #10409 — get_provider_registry() thread-safety race condition.
+
+This module implements the Behave steps that prove the race condition in
+``cleveragents.providers.registry.get_provider_registry``. Two concurrent
+callers can each observe ``_registry is None`` and independently construct a
+``ProviderRegistry``, violating the singleton contract.
+
+The implementation already holds ``_registry_lock`` around all reads and
+writes, so this scenario passes rather than fails; ``@tdd_expected_fail``
+is intentionally omitted. The test serves as a regression guard ensuring
+the lock is never removed.
+"""
+
+from __future__ import annotations
+
+import contextlib
+import threading
+from typing import Any
+from unittest.mock import MagicMock, patch
+
+from behave import given, then, when  # type: ignore[import-untyped]
+
+import cleveragents.providers.registry as _registry_module
+from cleveragents.providers.registry import (
+    ProviderRegistry,
+    get_provider_registry,
+    reset_provider_registry,
+)
+
+
+def _make_settings() -> Any:
+    """Return a minimal fake Settings object for ProviderRegistry construction."""
+    settings = MagicMock()
+    settings.openai_api_key = None
+    settings.anthropic_api_key = None
+    settings.google_api_key = None
+    settings.gemini_api_key = None
+    settings.azure_api_key = None
+    settings.openrouter_api_key = None
+    settings.cohere_api_key = None
+    settings.groq_api_key = None
+    settings.together_api_key = None
+    settings.default_provider = None
+    settings.default_model = None
+    settings.azure_openai_endpoint = None
+    settings.azure_openai_api_version = None
+    settings.azure_openai_deployment = None
+    settings.openrouter_organization = None
+    return settings
+
+
+@given("the global provider registry has been reset")
+def step_reset_global_registry(context: Any) -> None:
+    """Reset the global _registry singleton to None to simulate a fresh start."""
+    reset_provider_registry()
+    # Verify it is actually None
+    assert _registry_module._registry is None, (
+        "Expected _registry to be None after reset"
+    )
+
+
+@when("two threads call get_provider_registry() simultaneously")
+def step_two_threads_call_get_provider_registry(context: Any) -> None:
+    """Spawn two threads that call get_provider_registry() simultaneously.
+
+    A threading.Barrier is used to ensure both threads enter the function
+    body at the same time, maximising the chance of exposing the race
+    condition in the non-thread-safe singleton implementation.
+
+    The ProviderRegistry constructor is patched to introduce a small delay
+    (via a second barrier) so that both threads can observe ``_registry is
+    None`` before either has finished constructing the instance.
+    """
+    results: list[ProviderRegistry] = []
+    construction_count: list[int] = [0]
+    errors: list[Exception] = []
+
+    # Barrier to synchronise both threads at the entry point of
+    # get_provider_registry() so they both observe _registry is None.
+    entry_barrier = threading.Barrier(2, timeout=10)
+
+    # Barrier inside the ProviderRegistry constructor to ensure both threads
+    # have passed the ``if _registry is None`` check before either assigns
+    # the new instance to ``_registry``.
+    construction_barrier = threading.Barrier(2, timeout=10)
+
+    original_init = ProviderRegistry.__init__
+
+    def _slow_init(self: ProviderRegistry, settings: Any = None) -> None:
+        """Wrap __init__ to synchronise both threads mid-construction."""
+        construction_count[0] += 1
+        # Wait for the other thread to also enter __init__ before proceeding.
+        # This guarantees both threads have passed the ``_registry is None``
+        # guard in get_provider_registry() before either assigns the result.
+        with contextlib.suppress(threading.BrokenBarrierError):
+            construction_barrier.wait(timeout=10)
+        if settings is None:
+            settings = _make_settings()
+        original_init(self, settings)
+
+    def _thread_body() -> None:
+        try:
+            # Synchronise both threads at the entry of get_provider_registry()
+            with contextlib.suppress(threading.BrokenBarrierError):
+                entry_barrier.wait(timeout=10)
+            # Call without settings to trigger the race condition
+            registry = get_provider_registry()
+            results.append(registry)
+        except Exception as exc:  # pragma: no cover — defensive
+            errors.append(exc)
+
+    with (
+        patch.object(ProviderRegistry, "__init__", _slow_init),
+        patch(
+            "cleveragents.providers.registry.get_settings",
+            return_value=_make_settings(),
+        ),
+    ):
+        t1 = threading.Thread(
+            target=_thread_body, name="registry-thread-1", daemon=False
+        )
+        t2 = threading.Thread(
+            target=_thread_body, name="registry-thread-2", daemon=False
+        )
+        t1.start()
+        t2.start()
+        t1.join(timeout=15)
+        t2.join(timeout=15)
+
+    if errors:  # pragma: no cover — defensive
+        raise errors[0]
+
+    context.registry_results = results
+    context.registry_construction_count = construction_count[0]
+
+
+@then("both threads should receive the identical registry instance")
+def step_both_threads_same_instance(context: Any) -> None:
+    """Assert that both threads received the exact same ProviderRegistry object.
+
+    With ``_registry_lock`` in place the singleton contract holds, so this
+    assertion passes. It acts as a regression guard: removing the lock would
+    let two independent instances be created and trip this AssertionError.
+    """
+    results: list[ProviderRegistry] = context.registry_results
+    assert len(results) == 2, f"Expected 2 results from threads, got {len(results)}"
+    first_id = id(results[0])
+    second_id = id(results[1])
+    assert first_id == second_id, (
+        f"Race condition detected: two different ProviderRegistry instances were "
+        f"created (id={first_id} vs id={second_id}). The singleton is not "
+        f"thread-safe — both threads observed _registry is None and each "
+        f"independently constructed a new ProviderRegistry."
+    )
+
+
+@then("only one ProviderRegistry should have been constructed")
+def step_only_one_registry_constructed(context: Any) -> None:
+    """Assert that ProviderRegistry.__init__ was called exactly once.
+
+    With ``_registry_lock`` in place only one thread can enter the
+    ``if _registry is None`` branch, so the constructor runs exactly once and
+    this assertion passes. It acts as a regression guard: removing the lock
+    would let both threads call ProviderRegistry() and trip this
+    AssertionError.
+    """
+    count: int = context.registry_construction_count
+    assert count == 1, (
+        f"Race condition detected: ProviderRegistry was constructed {count} "
+        f"time(s) instead of exactly 1. Both threads entered the "
+        f"``if _registry is None`` branch simultaneously and each called "
+        f"ProviderRegistry(), violating the singleton contract."
+    )
diff --git a/features/steps/tdd_registry_thread_safety_steps.py b/features/steps/tdd_registry_thread_safety_steps.py
deleted file mode 100644
index 5e98d49c5..000000000
--- a/features/steps/tdd_registry_thread_safety_steps.py
+++ /dev/null
@@ -1,80 +0,0 @@
-"""Step definitions for TDD Issue #10409 — get_provider_registry() thread safety.
-
-Verifies that get_provider_registry() is safe for concurrent access from
-multiple threads, preventing the race condition where two threads can each
-observe _registry is None and independently construct a ProviderRegistry,
-violating the singleton contract.
-"""
-
-from __future__ import annotations
-
-import threading
-from typing import Any
-
-from behave import given, then, when
-
-from cleveragents.providers.registry import (
-    get_provider_registry,
-    reset_provider_registry,
-)
-
-__all__: list[str] = []
-
-
-@given("the global provider registry has been reset")
-def step_given_registry_reset(context: Any) -> None:
-    """Reset the global provider registry to None before the test."""
-    reset_provider_registry()
-    context.registry_instances: list[object] = []
-    context.construction_count = 0
-
-
-@when("two threads call get_provider_registry() simultaneously")
-def step_when_two_threads_call_simultaneously(context: Any) -> None:
-    """Spawn two threads that call get_provider_registry() at the same time."""
-    results: list[object] = []
-    results_lock = threading.Lock()
-    barrier = threading.Barrier(2)
-
-    def worker() -> None:
-        barrier.wait()  # Synchronise both threads to maximise race window
-        result = get_provider_registry()
-        with results_lock:
-            results.append(result)
-
-    threads = [threading.Thread(target=worker) for _ in range(2)]
-    for t in threads:
-        t.start()
-    for t in threads:
-        t.join()
-
-    context.registry_instances = results
-    # Count is always 1 with the lock fix; without the fix it could be 2
-    # We infer construction count from whether instances are identical
-    context.construction_count = (
-        1 if (len(results) == 2 and results[0] is results[1]) else 2
-    )
-
-
-@then("both threads should receive the identical registry instance")
-def step_then_same_instance(context: Any) -> None:
-    """Assert both threads received the exact same ProviderRegistry object."""
-    instances = context.registry_instances
-    assert len(instances) == 2, (
-        f"Expected 2 registry instances from threads, got {len(instances)}"
-    )
-    assert instances[0] is instances[1], (
-        f"Threads received different ProviderRegistry instances: "
-        f"id(instances[0])={id(instances[0])}, id(instances[1])={id(instances[1])}. "
-        f"This indicates a thread-safety race condition in get_provider_registry()."
-    )
-
-
-@then("only one ProviderRegistry should have been constructed")
-def step_then_one_construction(context: Any) -> None:
-    """Assert that only one ProviderRegistry was constructed."""
-    assert context.construction_count == 1, (
-        f"Expected exactly 1 ProviderRegistry construction, "
-        f"got {context.construction_count}. "
-        f"This indicates a thread-safety race condition in get_provider_registry()."
-    )
diff --git a/features/tdd_registry_thread_safety.feature b/features/tdd_registry_thread_safety.feature
deleted file mode 100644
index 164ac9fb1..000000000
--- a/features/tdd_registry_thread_safety.feature
+++ /dev/null
@@ -1,20 +0,0 @@
-@tdd_issue @tdd_issue_10409 @mock_only
-Feature: TDD Issue #10409 — get_provider_registry() singleton is not thread-safe
-  As a developer running concurrent agent workers
-  I want get_provider_registry() to be thread-safe
-  So that only one ProviderRegistry instance is ever created under concurrent access
-
-  This test captures bug #10478. The get_provider_registry() function in
-  cleveragents.providers.registry implements a singleton pattern without
-  thread-safety guards. Under concurrent access, two threads can each observe
-  _registry is None before either has finished constructing the ProviderRegistry,
-  causing both to independently instantiate a new registry. This violates the
-  singleton contract and can lead to inconsistent provider state.
-
-  See CONTRIBUTING.md > Bug Fix Workflow > TDD Issue Test Tags.
-
-  Scenario: Concurrent calls to get_provider_registry return the same instance
-    Given the global provider registry has been reset
-    When two threads call get_provider_registry() simultaneously
-    Then both threads should receive the identical registry instance
-    And only one ProviderRegistry should have been constructed