diff --git a/CHANGELOG.md b/CHANGELOG.md
index be1ec5b5..8c21d9ac 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -626,6 +626,11 @@ All notable changes to this project are documented here. The format is based on
   regression (`eef_delta_pose` + `rot6d` already reached the displacement
   clamp path before #143/#144). `euler_xyz` and `axis_angle` deltas have no
   such problem and remain guardrail-conformant.
+- **Agent policy configuration parameters now strictly reject non-strings**
+  in `LLMAgentPolicy` constructor, raising a guided `ConfigError` (#169). This
+  prevents unquoted CLI values (e.g., `-P model=42` or `-P api_key_env=false`)
+  from causing downstream errors or incorrect fallback logic, prompting the
+  user to pass quoted strings instead.
 - **An explicit invalid `--max-action-delta` now fails fast instead of silently
   running with weaker guardrails** (#154). Non-finite or non-positive values
   were previously caught by `_build_guardrails`'s degrade-per-component path
diff --git a/plugins/inspect-robots-agent/src/inspect_robots_agent/policy.py b/plugins/inspect-robots-agent/src/inspect_robots_agent/policy.py
index 4c7436a2..444c650b 100644
--- a/plugins/inspect-robots-agent/src/inspect_robots_agent/policy.py
+++ b/plugins/inspect-robots-agent/src/inspect_robots_agent/policy.py
@@ -340,6 +340,21 @@ def __init__(
         env: dict[str, str] | None = None,
         pre_check: PreCheck | None = None,
     ) -> None:
+        # Reject non-strings with a guided ConfigError to prevent unquoted CLI
+        # values (e.g. -P model=42) from causing downstream errors or silent bypasses.
+        for name, val in [
+            ("model", model),
+            ("base_url", base_url),
+            ("api_key_env", api_key_env),
+            ("speed", speed),
+        ]:
+            if val is not None and not isinstance(val, str):
+                raise ConfigError(
+                    f"{name} must be a string, got {val!r}.\n"
+                    f"fix: the -P parser coerces unquoted values; pass "
+                    f"-P '{name}=\"value\"'"
+                )
+
         prior_learnings_path: str | None = None
         prior_learnings_text: str | None = None
         prior_learnings_sha256: str | None = None
diff --git a/plugins/inspect-robots-agent/tests/test_anthropic.py b/plugins/inspect-robots-agent/tests/test_anthropic.py
index f37d227c..868601f3 100644
--- a/plugins/inspect-robots-agent/tests/test_anthropic.py
+++ b/plugins/inspect-robots-agent/tests/test_anthropic.py
@@ -1288,20 +1288,19 @@ def test_variant_strip_keeps_fine_tune_colons() -> None:
         )
 
 
-@pytest.mark.parametrize("api_key_env", [None, "", False, 0, 0.0])
+@pytest.mark.parametrize("api_key_env", [None, ""])
 def test_falsy_api_key_env_does_not_send_the_openrouter_key_to_a_gateway(
-    api_key_env: object,
+    api_key_env: str | None,
 ) -> None:
-    # '-P api_key_env=' parses to '', and 'false'/'0' to other falsy values,
-    # all of which resolve_provider treats as unset and answers with
-    # $OPENROUTER_API_KEY. An `is None` test would hand a third-party gateway
-    # the OpenRouter secret.
+    # '-P api_key_env=' parses to '', which resolve_provider treats as unset
+    # and answers with $OPENROUTER_API_KEY. An `is None` test would hand a
+    # third-party gateway the OpenRouter secret.
     seen, handler = _capture(_anthropic_response(_text("ok"), stop_reason="end_turn"))
     policy = LLMAgentPolicy(
         model="claude-opus-5",
         wire="messages",
         base_url="https://gw.example/v1",
-        api_key_env=api_key_env,  # type: ignore[arg-type]
+        api_key_env=api_key_env,
         transport=httpx.MockTransport(handler),
         env={"ANTHROPIC_API_KEY": "sk-ant", "OPENROUTER_API_KEY": "sk-or"},
     )
diff --git a/plugins/inspect-robots-agent/tests/test_policy_e2e.py b/plugins/inspect-robots-agent/tests/test_policy_e2e.py
index bd080fbf..5a0a3c39 100644
--- a/plugins/inspect-robots-agent/tests/test_policy_e2e.py
+++ b/plugins/inspect-robots-agent/tests/test_policy_e2e.py
@@ -2791,3 +2791,38 @@ def test_chat_wire_usage_metadata_counts_calls_only(tmp_path: Path) -> None:
     )
 
     assert sink.records[0].metadata["llm_usage"] == {"llm_calls": 2}
+
+
+@pytest.mark.parametrize(
+    "param, val",
+    [
+        ("model", 42),
+        ("model", 0),
+        ("base_url", True),
+        ("base_url", False),
+        ("api_key_env", True),
+        ("api_key_env", False),
+        ("speed", False),
+    ],
+)
+def test_non_string_params_rejected(param: str, val: Any) -> None:
+    kwargs: dict[str, Any] = {
+        "model": "test-model",
+        "base_url": "http://localhost:8000",
+        "api_key_env": "TEST_KEY",
+        "effort": "low",
+        "speed": None,
+        "wire": "chat",
+    }
+    kwargs[param] = val
+
+    # speed requires wire='anthropic'
+    if param == "speed":
+        kwargs["wire"] = "anthropic"
+
+    with pytest.raises(ConfigError) as exc_info:
+        LLMAgentPolicy(**kwargs)
+
+    assert f"{param} must be a string, got {val!r}." in str(exc_info.value)
+    expected_fix = f"fix: the -P parser coerces unquoted values; pass -P '{param}=\"value\"'"
+    assert expected_fix in str(exc_info.value)
diff --git a/tests/test_rerun_sink.py b/tests/test_rerun_sink.py
index c8c916df..662e3882 100644
--- a/tests/test_rerun_sink.py
+++ b/tests/test_rerun_sink.py
@@ -1861,6 +1861,7 @@ def test_real_rerun_accepts_the_blueprint(tmp_path: Path) -> None:
 def test_real_rerun_process_exits_when_tcp_peer_never_reads() -> None:
     """The real SDK atexit path is bounded after a connected peer stops reading."""
     rr = pytest.importorskip("rerun")
+
     if not hasattr(rr, "connect_grpc"):
         pytest.skip("pre-gRPC rerun-sdk cannot run the connect-mode wedge scenario")
     server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)