feat: Implement latency profiling and guardrails for performance monitoring

- Added synthetic latency profiler scenarios and CLI scripts for baseline generation and regression checks.
- Introduced latency baseline and threshold artifacts for CI enforcement.
- Enhanced CI workflow with latency guardrail checks.
- Updated documentation to include latency profiling commands and performance metrics.
- Added unit tests for latency guardrail evaluation.

tests/unit/test_latency_guardrails.py

@@ -0,0 +1,49 @@
+from __future__ import annotations
+
+from arbitrade.perf.guardrails import evaluate_guardrails
+from arbitrade.perf.latency import run_latency_profile
+
+
+def test_run_latency_profile_contains_expected_shape() -> None:
+    profile = run_latency_profile(iterations=50)
+
+    scenarios = profile.get("scenarios")
+    assert isinstance(scenarios, dict)
+    assert set(scenarios) == {
+        "book_update_burst",
+        "execution_spike",
+        "reconnect_storm",
+    }
+
+    for payload in scenarios.values():
+        assert isinstance(payload, dict)
+        stages = payload.get("stages")
+        assert isinstance(stages, dict)
+        assert "end_to_end" in stages
+
+
+def test_evaluate_guardrails_flags_regression() -> None:
+    baseline = {
+        "scenarios": {
+            "book_update_burst": {
+                "stages": {
+                    "end_to_end": {"p95_ms": 1.0, "p99_ms": 1.0},
+                }
+            }
+        }
+    }
+    current = {
+        "scenarios": {
+            "book_update_burst": {
+                "stages": {
+                    "end_to_end": {"p95_ms": 4.0, "p99_ms": 4.0},
+                }
+            }
+        }
+    }
+    thresholds = {"default": {"p95_ms": 2.0, "p99_ms": 2.0}}
+
+    failures = evaluate_guardrails(baseline=baseline, current=current, thresholds=thresholds)
+
+    assert failures
+    assert "latency regression" in failures[0]

tests/unit/test_settings_validation.py

@@ -11,7 +11,11 @@ def test_dashboard_auth_requires_both_fields() -> None:
 
 def test_kraken_api_auth_requires_key_and_secret() -> None:
     with pytest.raises(ValidationError):
-        Settings(_env_file=None, KRAKEN_API_KEY="key-only")
+        Settings(
+            _env_file=None,
+            KRAKEN_API_KEY="key-only",
+            KRAKEN_API_SECRET="",
+        )
 
 
 def test_kraken_permissions_require_query_and_trade() -> None: