security: implement pentest remediation (RATE-002, CLI-001)

RATE-002: Proactive rate limit cleanup when entries exceed threshold
- Add RATE_LIMIT_CLEANUP_THRESHOLD config (default 0.8)
- Trigger cleanup before hitting hard limit
- Prevents memory exhaustion under sustained load

CLI-001: Validate clipboard tool paths against trusted directories
- Add TRUSTED_CLIPBOARD_DIRS for Unix system paths
- Add TRUSTED_WINDOWS_PATTERNS for Windows validation
- Reject tools in user-writable locations (PATH hijack prevention)
- Use absolute paths in subprocess calls

tests/test_rate_limiting.py

@@ -267,3 +267,75 @@ class TestRateLimitMaxEntries:
         finally:
             app.config["RATE_LIMIT_MAX_ENTRIES"] = original_max
             reset_rate_limits()
+
+
+class TestRateLimitCleanupThreshold:
+    """Tests for RATE-002: automatic cleanup trigger when threshold exceeded."""
+
+    def test_cleanup_threshold_config_exists(self, app):
+        """RATE_LIMIT_CLEANUP_THRESHOLD config should exist."""
+        assert "RATE_LIMIT_CLEANUP_THRESHOLD" in app.config
+        threshold = app.config["RATE_LIMIT_CLEANUP_THRESHOLD"]
+        assert isinstance(threshold, float)
+        assert 0.0 < threshold <= 1.0
+
+    def test_proactive_cleanup_at_threshold(self, app):
+        """Cleanup triggers proactively when threshold exceeded."""
+        from app.api.routes import (
+            _rate_limit_requests,
+            check_rate_limit,
+            reset_rate_limits,
+        )
+
+        reset_rate_limits()
+
+        original_max = app.config.get("RATE_LIMIT_MAX_ENTRIES", 10000)
+        original_threshold = app.config.get("RATE_LIMIT_CLEANUP_THRESHOLD", 0.8)
+
+        # Set max to 10, threshold to 0.5 (cleanup at 5 entries)
+        app.config["RATE_LIMIT_MAX_ENTRIES"] = 10
+        app.config["RATE_LIMIT_CLEANUP_THRESHOLD"] = 0.5
+
+        try:
+            with app.app_context():
+                # Add 6 entries (exceeds 50% threshold of 10)
+                for i in range(6):
+                    check_rate_limit(f"10.0.0.{i}", authenticated=False)
+
+                # Threshold cleanup should have triggered, reducing count
+                # Cleanup prunes to threshold/2 = 2-3 entries
+                assert len(_rate_limit_requests) < 6
+        finally:
+            app.config["RATE_LIMIT_MAX_ENTRIES"] = original_max
+            app.config["RATE_LIMIT_CLEANUP_THRESHOLD"] = original_threshold
+            reset_rate_limits()
+
+    def test_no_cleanup_below_threshold(self, app):
+        """No cleanup when below threshold."""
+        from app.api.routes import (
+            _rate_limit_requests,
+            check_rate_limit,
+            reset_rate_limits,
+        )
+
+        reset_rate_limits()
+
+        original_max = app.config.get("RATE_LIMIT_MAX_ENTRIES", 10000)
+        original_threshold = app.config.get("RATE_LIMIT_CLEANUP_THRESHOLD", 0.8)
+
+        # Set max to 20, threshold to 0.8 (cleanup at 16 entries)
+        app.config["RATE_LIMIT_MAX_ENTRIES"] = 20
+        app.config["RATE_LIMIT_CLEANUP_THRESHOLD"] = 0.8
+
+        try:
+            with app.app_context():
+                # Add 5 entries (below 80% threshold of 20 = 16)
+                for i in range(5):
+                    check_rate_limit(f"10.0.0.{i}", authenticated=False)
+
+                # All 5 entries should remain (no cleanup triggered)
+                assert len(_rate_limit_requests) == 5
+        finally:
+            app.config["RATE_LIMIT_MAX_ENTRIES"] = original_max
+            app.config["RATE_LIMIT_CLEANUP_THRESHOLD"] = original_threshold
+            reset_rate_limits()