diff --git a/benchmarks/tdd_actor_list_validation_bench.py b/benchmarks/tdd_actor_list_validation_bench.py
new file mode 100644
index 000000000..31be25fea
--- /dev/null
+++ b/benchmarks/tdd_actor_list_validation_bench.py
@@ -0,0 +1,74 @@
+"""ASV benchmarks for TDD Bug #592 — actor list validation error.
+
+Measures the performance of ``ActorRegistry.list_actors()`` when a provider
+has a default model containing ``/`` characters.  Establishes a baseline
+before and after the bug fix.
+
+Root cause: ``_actor_name()`` builds names via ``f"{provider}/{model}"``.
+Multi-slash model names produce actor names with 2+ slashes, which
+``ActorService._normalize_name()`` rejects with a ``ValidationError``.
+"""
+
+from __future__ import annotations
+
+import contextlib
+import sys
+from pathlib import Path
+
+from pydantic import ValidationError
+
+# Ensure the local *source* tree is importable even when ASV has an
+# older build of the package installed.
+_SRC = str(Path(__file__).resolve().parents[1] / "src")
+if _SRC not in sys.path:
+    sys.path.insert(0, _SRC)
+
+# Ensure the features directory is importable so we can reuse shared
+# mock stubs instead of duplicating them locally.
+_FEATURES = str(Path(__file__).resolve().parents[1] / "features")
+if _FEATURES not in sys.path:
+    sys.path.insert(0, _FEATURES)
+
+from mocks.fake_provider import FakeProviderInfo, make_registry  # noqa: E402
+
+
+class TDDActorListValidationSuite:
+    """Benchmark actor list with multi-slash provider models (TDD bug #592)."""
+
+    timeout = 60
+
+    def setup(self) -> None:
+        _, self._empty_registry = make_registry()
+        _, self._slash_registry = make_registry(
+            providers=[
+                FakeProviderInfo(
+                    name="Openrouter",
+                    default_model="anthropic/claude-sonnet-4-20250514",
+                ),
+            ]
+        )
+
+    def time_list_empty(self) -> None:
+        """List actors with zero configured providers."""
+        self._empty_registry.list_actors()
+
+    def time_list_multi_slash_provider(self) -> None:
+        """List actors when a multi-slash provider is configured."""
+        with contextlib.suppress(ValidationError):
+            self._slash_registry.list_actors()
+
+    def track_multi_slash_succeeds(self) -> int:
+        """Track whether listing with a multi-slash provider succeeds.
+
+        Returns 1 when ``list_actors()`` completes without error; 0 if
+        ``ValidationError`` is raised.
+        """
+        try:
+            self._slash_registry.list_actors()
+            return 1
+        except ValidationError:
+            return 0
+
+
+_track = TDDActorListValidationSuite.track_multi_slash_succeeds
+_track.unit = "success"  # type: ignore[attr-defined]
diff --git a/benchmarks/tdd_session_create_di_bench.py b/benchmarks/tdd_session_create_di_bench.py
index 49e23ddc9..7409688ed 100644
--- a/benchmarks/tdd_session_create_di_bench.py
+++ b/benchmarks/tdd_session_create_di_bench.py
@@ -10,9 +10,8 @@ from __future__ import annotations
 from unittest.mock import MagicMock
 
 from benchmarks._session_bench_common import mock_session, runner
-
-from cleveragents.cli.commands import session as session_mod  # noqa: E402
-from cleveragents.cli.commands.session import app as session_app  # noqa: E402
+from cleveragents.cli.commands import session as session_mod
+from cleveragents.cli.commands.session import app as session_app
 
 
 class TDDSessionCreateDISuite:
diff --git a/features/mocks/fake_provider.py b/features/mocks/fake_provider.py
index 48168efed..b991cf5b6 100644
--- a/features/mocks/fake_provider.py
+++ b/features/mocks/fake_provider.py
@@ -11,6 +11,8 @@ from dataclasses import dataclass, field
 from typing import Any
 from unittest.mock import MagicMock
 
+from cleveragents.actor.registry import ActorRegistry
+from cleveragents.domain.models.core.actor import Actor
 from cleveragents.providers.registry import ProviderCapabilities
 
 
@@ -22,6 +24,7 @@ class FakeProviderInfo:
     default_model: str
     provider_type: Any = None
     capabilities: Any = None
+    api_key_env_var: str = ""
 
     def __post_init__(self) -> None:
         if self.provider_type is None:
@@ -38,3 +41,48 @@ class FakeProviderRegistry:
 
     def get_configured_providers(self) -> list[FakeProviderInfo]:
         return self.providers
+
+
+def make_registry(
+    providers: list[FakeProviderInfo] | None = None,
+) -> tuple[MagicMock, ActorRegistry]:
+    """Build a real ``ActorRegistry`` with mocked service/settings.
+
+    The ``ActorService`` is mocked so there is no database dependency, but
+    the ``ActorRegistry`` code (including ``_actor_name()``) runs for real.
+
+    Actors successfully created by ``upsert_actor`` are captured so that
+    ``list_actors`` returns them — ensuring Scenario 3 ("valid JSON") can
+    detect when the bug is actually fixed.
+    """
+    provider_reg = FakeProviderRegistry(providers=providers or [])
+
+    captured_actors: list[Actor] = []
+
+    def _capturing_upsert(**kwargs: Any) -> Actor:
+        actor = Actor(
+            name=kwargs.get("name", "mock/actor"),
+            provider=kwargs.get("provider", "mock"),
+            model=kwargs.get("model", "actor"),
+            config_blob={},
+            config_hash=Actor.compute_hash({}),
+        )
+        captured_actors.append(actor)
+        return actor
+
+    mock_service = MagicMock()
+    mock_service.list_actors.side_effect = lambda: list(captured_actors)
+    mock_service.get_default_actor.return_value = None
+    mock_service.upsert_actor.side_effect = _capturing_upsert
+
+    mock_settings = MagicMock()
+    mock_settings.resolve_provider_defaults.return_value = MagicMock(
+        provider=None, model=None
+    )
+
+    registry = ActorRegistry(
+        actor_service=mock_service,
+        provider_registry=provider_reg,
+        settings=mock_settings,
+    )
+    return mock_service, registry
diff --git a/features/steps/tdd_actor_list_validation_steps.py b/features/steps/tdd_actor_list_validation_steps.py
new file mode 100644
index 000000000..c94ade2e0
--- /dev/null
+++ b/features/steps/tdd_actor_list_validation_steps.py
@@ -0,0 +1,140 @@
+"""Step definitions for TDD Bug #592 — actor list validation error.
+
+These steps exercise the *real* ``ActorRegistry._actor_name()`` code path
+with a provider whose default model name contains ``/`` characters.  The
+``@tdd_expected_fail`` tag on the scenarios inverts the result: these tests
+**pass** CI while the bug is present and will **fail** once the bug is fixed
+(signalling that the tag should be removed).
+
+Root cause
+~~~~~~~~~~
+``ActorRegistry._actor_name()`` builds names via
+``f"{provider}/{model}"``.  For providers whose default model already
+contains ``/`` (e.g. OpenRouter's ``anthropic/claude-sonnet-4-20250514``),
+the result has 2+ slashes.  ``ActorService._normalize_name()`` then raises
+``ValidationError("Actor names must include exactly one '/' separator")``.
+"""
+
+from __future__ import annotations
+
+import json
+from typing import Any
+from unittest.mock import patch
+
+from behave import given, then, when
+from typer.testing import CliRunner
+
+from cleveragents.cli.commands.actor import app as actor_app
+from features.mocks.fake_provider import FakeProviderInfo, make_registry
+
+runner = CliRunner()
+
+_PATCH_GET_SERVICES = "cleveragents.cli.commands.actor._get_services"
+
+
+# ---------------------------------------------------------------------------
+# Given steps
+# ---------------------------------------------------------------------------
+
+
+@given("an actor registry with a multi-slash model provider for tdd-actor-validation")
+def step_multi_slash_provider(context: Any) -> None:
+    """Set up a real ``ActorRegistry`` with a multi-slash model provider.
+
+    The provider name is ``Openrouter`` and the default model is
+    ``anthropic/claude-sonnet-4-20250514`` — reproducing the exact
+    combination that triggers bug #592.
+    """
+    fake_provider = FakeProviderInfo(
+        name="Openrouter",
+        default_model="anthropic/claude-sonnet-4-20250514",
+    )
+    service, registry = make_registry([fake_provider])
+    context.tdd_actor_service = service
+    context.tdd_actor_registry = registry
+
+
+# ---------------------------------------------------------------------------
+# When steps
+# ---------------------------------------------------------------------------
+
+
+@when("I run actor list via the tdd-actor-validation CLI")
+def step_run_actor_list(context: Any) -> None:
+    """Invoke ``actor list`` with the prepared registry."""
+    with patch(
+        _PATCH_GET_SERVICES,
+        return_value=(
+            context.tdd_actor_service,
+            context.tdd_actor_registry,
+        ),
+    ):
+        context.tdd_actor_result = runner.invoke(actor_app, ["list"])
+
+
+@when("I run actor list with format json via the tdd-actor-validation CLI")
+def step_run_actor_list_json(context: Any) -> None:
+    """Invoke ``actor list --format json`` with the prepared registry."""
+    with patch(
+        _PATCH_GET_SERVICES,
+        return_value=(
+            context.tdd_actor_service,
+            context.tdd_actor_registry,
+        ),
+    ):
+        context.tdd_actor_result = runner.invoke(
+            actor_app, ["list", "--format", "json"]
+        )
+
+
+# ---------------------------------------------------------------------------
+# Then steps
+# ---------------------------------------------------------------------------
+
+
+@then("the tdd-actor-validation exit code should be {code:d}")
+def step_exit_code(context: Any, code: int) -> None:
+    result = context.tdd_actor_result
+    assert result is not None, "actor list was not invoked"
+    actual = result.exit_code
+    assert actual == code, (
+        f"Expected exit code {code}, got {actual}. Output:\n{result.output}"
+    )
+
+
+@then('the tdd-actor-validation output should not contain "{text}"')
+def step_output_not_contains(context: Any, text: str) -> None:
+    result = context.tdd_actor_result
+    assert result is not None, "actor list was not invoked"
+    output = result.output
+    assert text.lower() not in output.lower(), (
+        f"Did NOT expect '{text}' in output but found it:\n{output}"
+    )
+
+
+@then("the tdd-actor-validation upserted actor name should contain exactly one slash")
+def step_upserted_name_single_slash(context: Any) -> None:
+    """Verify that every name passed to ``upsert_actor`` has exactly one ``/``.
+
+    With the bug present, ``_actor_name()`` produces names like
+    ``Openrouter/anthropic/claude-sonnet-4-20250514`` (2+ slashes), so this
+    assertion fails — which the ``@tdd_expected_fail`` tag inverts to a pass.
+    """
+    service = context.tdd_actor_service
+    assert service.upsert_actor.call_count > 0, "upsert_actor was never called"
+    for call in service.upsert_actor.call_args_list:
+        name = call.kwargs.get("name") or call.args[0]
+        slash_count = name.count("/")
+        assert slash_count == 1, (
+            f"Expected exactly 1 slash in actor name '{name}', found {slash_count}"
+        )
+
+
+@then("the tdd-actor-validation output should be valid JSON")
+def step_output_valid_json(context: Any) -> None:
+    result = context.tdd_actor_result
+    assert result is not None, "actor list was not invoked"
+    try:
+        json.loads(result.output)
+    except json.JSONDecodeError as exc:
+        raise AssertionError(f"Output is not valid JSON:\n{result.output}") from exc
diff --git a/features/tdd_actor_list_validation.feature b/features/tdd_actor_list_validation.feature
new file mode 100644
index 000000000..46bc8582d
--- /dev/null
+++ b/features/tdd_actor_list_validation.feature
@@ -0,0 +1,32 @@
+@tdd_bug @tdd_bug_592
+Feature: TDD Bug #592 — actor list validation rejects multi-slash model names
+  As a developer
+  I want to verify that `agents actor list` raises a validation error when
+  a provider has a model name containing `/` separators
+  So that the bug is captured and will be caught by a regression test
+
+  The root cause is that `ActorRegistry._actor_name()` builds actor names
+  via `f"{provider}/{model}"`.  When a provider's default model already
+  contains `/` (e.g. `anthropic/claude-sonnet-4-20250514`), the resulting
+  name has 2+ slashes and `ActorService._normalize_name()` rejects it with
+  `ValidationError("Actor names must include exactly one '/' separator")`.
+
+  @tdd_expected_fail
+  Scenario: Actor list with multi-slash model does not raise validation error
+    Given an actor registry with a multi-slash model provider for tdd-actor-validation
+    When I run actor list via the tdd-actor-validation CLI
+    Then the tdd-actor-validation exit code should be 0
+    And the tdd-actor-validation output should not contain "VALIDATION_FAILED"
+
+  @tdd_expected_fail
+  Scenario: Built-in actor names have exactly one slash separator
+    Given an actor registry with a multi-slash model provider for tdd-actor-validation
+    When I run actor list via the tdd-actor-validation CLI
+    Then the tdd-actor-validation upserted actor name should contain exactly one slash
+
+  @tdd_expected_fail
+  Scenario: Actor list JSON format with multi-slash model succeeds
+    Given an actor registry with a multi-slash model provider for tdd-actor-validation
+    When I run actor list with format json via the tdd-actor-validation CLI
+    Then the tdd-actor-validation exit code should be 0
+    And the tdd-actor-validation output should be valid JSON
diff --git a/robot/helper_tdd_actor_list_validation.py b/robot/helper_tdd_actor_list_validation.py
new file mode 100644
index 000000000..2fb7e6d0d
--- /dev/null
+++ b/robot/helper_tdd_actor_list_validation.py
@@ -0,0 +1,169 @@
+"""Helper script for tdd_actor_list_validation.robot smoke tests.
+
+Each subcommand exercises the real ``ActorRegistry._actor_name()`` code path
+with a provider whose default model contains ``/`` characters to reproduce
+bug #592.  The helper reports the **real** outcome: it exits 0 and prints
+the sentinel when the operation succeeds (bug is fixed), and exits 1 when
+the bug is still present.  The ``tdd_expected_fail_listener`` on the Robot
+side handles pass/fail inversion while the bug remains open.
+"""
+
+from __future__ import annotations
+
+import sys
+from collections.abc import Callable
+from pathlib import Path
+from typing import Any
+from unittest.mock import patch
+
+# Ensure local source tree is importable
+_SRC = str(Path(__file__).resolve().parents[1] / "src")
+if _SRC not in sys.path:
+    sys.path.insert(0, _SRC)
+
+# Ensure the features directory is importable for shared mocks
+_FEATURES = str(Path(__file__).resolve().parents[1] / "features")
+if _FEATURES not in sys.path:
+    sys.path.insert(0, _FEATURES)
+
+from mocks.fake_provider import FakeProviderInfo, make_registry  # noqa: E402
+from typer.testing import CliRunner  # noqa: E402
+
+from cleveragents.cli.commands.actor import app as actor_app  # noqa: E402
+
+runner = CliRunner()
+
+_PATCH_GET_SERVICES = "cleveragents.cli.commands.actor._get_services"
+
+_MULTI_SLASH_PROVIDERS = [
+    FakeProviderInfo(
+        name="Openrouter",
+        default_model="anthropic/claude-sonnet-4-20250514",
+    ),
+]
+
+
+# ---------------------------------------------------------------------------
+# Subcommands
+# ---------------------------------------------------------------------------
+
+
+def list_validation_error() -> None:
+    """Invoke ``actor list`` with a multi-slash model provider.
+
+    Exits 0 with sentinel when the command succeeds with valid names (bug
+    fixed).  Exits 1 when the command fails or produces bad names (bug
+    still present).
+    """
+    mock_service, registry = make_registry(_MULTI_SLASH_PROVIDERS)
+    with patch(
+        _PATCH_GET_SERVICES,
+        return_value=(mock_service, registry),
+    ):
+        result = runner.invoke(actor_app, ["list"])
+    assert mock_service.upsert_actor.call_count > 0, (
+        "upsert_actor was never called — patch may not have taken effect"
+    )
+    if result.exit_code != 0:
+        # Bug present — command failed.
+        print(
+            f"actor list failed with exit code {result.exit_code}",
+            file=sys.stderr,
+        )
+        sys.exit(1)
+    # Command succeeded — check if names are valid (single slash).
+    for call in mock_service.upsert_actor.call_args_list:
+        name: Any = call.kwargs.get("name", "")
+        if name.count("/") != 1:
+            print(
+                f"actor list produced bad name {name!r} with {name.count('/')} slashes",
+                file=sys.stderr,
+            )
+            sys.exit(1)
+    # Bug fixed — command succeeded with valid names.
+    print("tdd-actor-list-validation-error-ok")
+
+
+def name_slash_check() -> None:
+    """Verify that upserted actor names have exactly one ``/``.
+
+    Exits 0 with sentinel when all names have exactly one slash (bug
+    fixed).  Exits 1 when any name has 0 or 2+ slashes (bug still
+    present).
+    """
+    mock_service, registry = make_registry(_MULTI_SLASH_PROVIDERS)
+    with patch(
+        _PATCH_GET_SERVICES,
+        return_value=(mock_service, registry),
+    ):
+        runner.invoke(actor_app, ["list"])
+
+    assert mock_service.upsert_actor.call_count > 0, (
+        "upsert_actor was never called — patch may not have taken effect"
+    )
+    for call in mock_service.upsert_actor.call_args_list:
+        name: Any = call.kwargs.get("name", "")
+        if name.count("/") != 1:
+            # Bug present — name construction produces bad names.
+            print(
+                f"actor name {name!r} has {name.count('/')} slashes",
+                file=sys.stderr,
+            )
+            sys.exit(1)
+    # Bug fixed — all names have exactly one slash.
+    print("tdd-actor-name-slash-check-ok")
+
+
+def list_json_validation() -> None:
+    """Invoke ``actor list --format json`` with a multi-slash model provider.
+
+    Exits 0 with sentinel when the command succeeds with valid names (bug
+    fixed).  Exits 1 when the command fails or produces bad names (bug
+    still present).
+    """
+    mock_service, registry = make_registry(_MULTI_SLASH_PROVIDERS)
+    with patch(
+        _PATCH_GET_SERVICES,
+        return_value=(mock_service, registry),
+    ):
+        result = runner.invoke(actor_app, ["list", "--format", "json"])
+    assert mock_service.upsert_actor.call_count > 0, (
+        "upsert_actor was never called — patch may not have taken effect"
+    )
+    if result.exit_code != 0:
+        # Bug present — command failed.
+        print(
+            f"actor list --format json failed with exit code {result.exit_code}",
+            file=sys.stderr,
+        )
+        sys.exit(1)
+    # Command succeeded — check if names are valid (single slash).
+    for call in mock_service.upsert_actor.call_args_list:
+        name: Any = call.kwargs.get("name", "")
+        if name.count("/") != 1:
+            print(
+                f"actor list --format json produced bad name {name!r} with "
+                f"{name.count('/')} slashes",
+                file=sys.stderr,
+            )
+            sys.exit(1)
+    # Bug fixed — command succeeded with valid names.
+    print("tdd-actor-list-json-validation-ok")
+
+
+# ---------------------------------------------------------------------------
+# Dispatcher
+# ---------------------------------------------------------------------------
+
+_COMMANDS: dict[str, Callable[[], None]] = {
+    "list-validation-error": list_validation_error,
+    "name-slash-check": name_slash_check,
+    "list-json-validation": list_json_validation,
+}
+
+if __name__ == "__main__":
+    if len(sys.argv) < 2 or sys.argv[1] not in _COMMANDS:
+        print(f"Usage: {sys.argv[0]} <{'|'.join(_COMMANDS)}>", file=sys.stderr)
+        sys.exit(1)
+    cmd = _COMMANDS[sys.argv[1]]
+    cmd()
diff --git a/robot/tdd_actor_list_validation.robot b/robot/tdd_actor_list_validation.robot
new file mode 100644
index 000000000..08e477ec9
--- /dev/null
+++ b/robot/tdd_actor_list_validation.robot
@@ -0,0 +1,43 @@
+*** Settings ***
+Documentation    TDD Bug #592 — actor list validation rejects multi-slash model names
+...              Integration smoke tests verifying that the actor list command
+...              raises a validation error when a provider has a multi-slash
+...              default model name.  These tests are tagged ``tdd_expected_fail``
+...              and are expected to fail until bug #592 is fixed.
+Resource         ${CURDIR}/common.resource
+Suite Setup      Setup Test Environment
+Suite Teardown   Cleanup Test Environment
+
+*** Variables ***
+${HELPER}    ${CURDIR}/helper_tdd_actor_list_validation.py
+
+*** Test Cases ***
+TDD Actor List Validation Error With Multi-Slash Model
+    [Documentation]    Verify that ``actor list`` triggers a validation error
+    ...                when a provider's default model contains ``/`` characters.
+    [Tags]    tdd_bug    tdd_bug_592    tdd_expected_fail
+    ${result}=    Run Process    ${PYTHON}    ${HELPER}    list-validation-error    cwd=${WORKSPACE}
+    Log    ${result.stdout}
+    Log    ${result.stderr}
+    Should Be Equal As Integers    ${result.rc}    0
+    Should Contain    ${result.stdout}    tdd-actor-list-validation-error-ok
+
+TDD Actor Name Slash Count Check
+    [Documentation]    Verify that built-in actor names have exactly one ``/``
+    ...                separator after construction by ``_actor_name()``.
+    [Tags]    tdd_bug    tdd_bug_592    tdd_expected_fail
+    ${result}=    Run Process    ${PYTHON}    ${HELPER}    name-slash-check    cwd=${WORKSPACE}
+    Log    ${result.stdout}
+    Log    ${result.stderr}
+    Should Be Equal As Integers    ${result.rc}    0
+    Should Contain    ${result.stdout}    tdd-actor-name-slash-check-ok
+
+TDD Actor List JSON With Multi-Slash Model
+    [Documentation]    Verify that ``actor list --format json`` triggers a
+    ...                validation error with a multi-slash model provider.
+    [Tags]    tdd_bug    tdd_bug_592    tdd_expected_fail
+    ${result}=    Run Process    ${PYTHON}    ${HELPER}    list-json-validation    cwd=${WORKSPACE}
+    Log    ${result.stdout}
+    Log    ${result.stderr}
+    Should Be Equal As Integers    ${result.rc}    0
+    Should Contain    ${result.stdout}    tdd-actor-list-json-validation-ok