diff --git a/tests/unit/test_models.py b/tests/unit/test_models.py
index d71d12d..9a4f891 100644
--- a/tests/unit/test_models.py
+++ b/tests/unit/test_models.py
@@ -445,6 +445,15 @@ class TestQueryParametersValidation:
                 max_bedrooms=3,
             )
 
+    def test_invalid_sqm_range_raises(self) -> None:
+        """min_sqm > max_sqm should raise ValidationError."""
+        with pytest.raises(ValidationError, match="min_sqm.*must be <= max_sqm"):
+            QueryParameters(
+                listing_type=ListingType.RENT,
+                min_sqm=100,
+                max_sqm=50,
+            )
+
 
 class TestDestinationMode:
     """Tests for DestinationMode."""
diff --git a/tests/unit/test_passkey_error_handling.py b/tests/unit/test_passkey_error_handling.py
new file mode 100644
index 0000000..a991a5a
--- /dev/null
+++ b/tests/unit/test_passkey_error_handling.py
@@ -0,0 +1,71 @@
+"""Unit tests for passkey route error handling."""
+from unittest.mock import patch, MagicMock
+
+import pytest
+from starlette.testclient import TestClient
+
+# We need to test through the FastAPI app or build a minimal test client
+from api.passkey_routes import passkey_router
+from fastapi import FastAPI
+
+
+def _build_app() -> FastAPI:
+    app = FastAPI()
+    app.include_router(passkey_router)
+    return app
+
+
+class TestPasskeyErrorHandling:
+    """Tests that passkey routes return generic error messages for internal exceptions."""
+
+    @patch("api.passkey_routes.passkey_service")
+    @patch("api.passkey_routes.UserRepository")
+    def test_register_begin_internal_error_returns_generic_message(
+        self, mock_user_repo: MagicMock, mock_service: MagicMock
+    ) -> None:
+        mock_service.begin_registration.side_effect = RuntimeError("DB connection lost")
+        client = TestClient(_build_app())
+        resp = client.post("/api/passkey/register/begin", json={"email": "test@example.com"})
+        assert resp.status_code == 400
+        assert resp.json()["detail"] == "Registration failed. Please try again."
+        assert "DB connection lost" not in resp.json()["detail"]
+
+    @patch("api.passkey_routes.passkey_service")
+    @patch("api.passkey_routes.UserRepository")
+    def test_register_begin_value_error_returns_user_message(
+        self, mock_user_repo: MagicMock, mock_service: MagicMock
+    ) -> None:
+        mock_service.begin_registration.side_effect = ValueError("Email already registered")
+        client = TestClient(_build_app())
+        resp = client.post("/api/passkey/register/begin", json={"email": "test@example.com"})
+        assert resp.status_code == 400
+        assert resp.json()["detail"] == "Email already registered"
+
+    @patch("api.passkey_routes.passkey_service")
+    @patch("api.passkey_routes.UserRepository")
+    def test_login_complete_internal_error_returns_generic_message(
+        self, mock_user_repo: MagicMock, mock_service: MagicMock
+    ) -> None:
+        mock_service.complete_authentication.side_effect = RuntimeError("Crypto failure")
+        client = TestClient(_build_app())
+        resp = client.post(
+            "/api/passkey/login/complete",
+            json={"session_id": "abc", "credential": {"id": "x"}},
+        )
+        assert resp.status_code == 400
+        assert resp.json()["detail"] == "Login could not be completed."
+        assert "Crypto failure" not in resp.json()["detail"]
+
+    @patch("api.passkey_routes.passkey_service")
+    @patch("api.passkey_routes.UserRepository")
+    def test_login_complete_value_error_returns_user_message(
+        self, mock_user_repo: MagicMock, mock_service: MagicMock
+    ) -> None:
+        mock_service.complete_authentication.side_effect = ValueError("Invalid credential")
+        client = TestClient(_build_app())
+        resp = client.post(
+            "/api/passkey/login/complete",
+            json={"session_id": "abc", "credential": {"id": "x"}},
+        )
+        assert resp.status_code == 400
+        assert resp.json()["detail"] == "Invalid credential"
diff --git a/tests/unit/test_poi_validation.py b/tests/unit/test_poi_validation.py
new file mode 100644
index 0000000..e1cfe62
--- /dev/null
+++ b/tests/unit/test_poi_validation.py
@@ -0,0 +1,58 @@
+"""Unit tests for POI request validation."""
+import pytest
+from pydantic import ValidationError
+
+from api.poi_routes import CreatePOIRequest, UpdatePOIRequest
+
+
+class TestCreatePOIValidation:
+    """Tests for CreatePOIRequest field validation."""
+
+    def test_valid_request(self) -> None:
+        req = CreatePOIRequest(name="Office", address="123 Main St", latitude=51.5, longitude=-0.1)
+        assert req.name == "Office"
+
+    def test_name_too_long(self) -> None:
+        with pytest.raises(ValidationError):
+            CreatePOIRequest(name="A" * 201, address="addr", latitude=0, longitude=0)
+
+    def test_address_too_long(self) -> None:
+        with pytest.raises(ValidationError):
+            CreatePOIRequest(name="ok", address="A" * 501, latitude=0, longitude=0)
+
+    def test_latitude_too_high(self) -> None:
+        with pytest.raises(ValidationError):
+            CreatePOIRequest(name="ok", address="addr", latitude=91.0, longitude=0)
+
+    def test_latitude_too_low(self) -> None:
+        with pytest.raises(ValidationError):
+            CreatePOIRequest(name="ok", address="addr", latitude=-91.0, longitude=0)
+
+    def test_longitude_too_high(self) -> None:
+        with pytest.raises(ValidationError):
+            CreatePOIRequest(name="ok", address="addr", latitude=0, longitude=181.0)
+
+    def test_longitude_too_low(self) -> None:
+        with pytest.raises(ValidationError):
+            CreatePOIRequest(name="ok", address="addr", latitude=0, longitude=-181.0)
+
+
+class TestUpdatePOIValidation:
+    """Tests for UpdatePOIRequest field validation."""
+
+    def test_valid_partial_update(self) -> None:
+        req = UpdatePOIRequest(name="New Name")
+        assert req.name == "New Name"
+        assert req.latitude is None
+
+    def test_name_too_long(self) -> None:
+        with pytest.raises(ValidationError):
+            UpdatePOIRequest(name="A" * 201)
+
+    def test_latitude_out_of_range(self) -> None:
+        with pytest.raises(ValidationError):
+            UpdatePOIRequest(latitude=91.0)
+
+    def test_longitude_out_of_range(self) -> None:
+        with pytest.raises(ValidationError):
+            UpdatePOIRequest(longitude=181.0)
diff --git a/tests/unit/test_rate_limiter.py b/tests/unit/test_rate_limiter.py
index 68b0b57..d3a8011 100644
--- a/tests/unit/test_rate_limiter.py
+++ b/tests/unit/test_rate_limiter.py
@@ -30,6 +30,7 @@ def _make_config(**overrides: object) -> RateLimitConfig:
         "geojson_stream_batch_size_cap": 200,
         "rate_limit_redis_db": 3,
         "metrics_allowed_ips": "127.0.0.1",
+        "trusted_proxy_depth": 1,
     }
     defaults.update(overrides)
     return RateLimitConfig(**defaults)  # type: ignore[arg-type]
@@ -236,3 +237,92 @@ class TestRateLimitConfig:
         # Should fall back to default
         assert config.endpoint_limits["/api/listing"].max_requests == 30
         assert config.endpoint_limits["/api/listing"].window_seconds == 60
+
+
+from api.rate_limiter import _client_ip
+
+
+class TestClientIp:
+    """Tests for _client_ip with trusted proxy depth."""
+
+    def test_uses_rightmost_ip_with_depth_1(self) -> None:
+        scope = {
+            "type": "http",
+            "headers": [(b"x-forwarded-for", b"spoofed.ip, proxy1, real.ip")],
+        }
+        request = Request(scope)
+        assert _client_ip(request, depth=1) == "real.ip"
+
+    def test_uses_second_from_right_with_depth_2(self) -> None:
+        scope = {
+            "type": "http",
+            "headers": [(b"x-forwarded-for", b"spoofed.ip, real.ip, proxy1")],
+        }
+        request = Request(scope)
+        assert _client_ip(request, depth=2) == "real.ip"
+
+    def test_falls_back_to_connection_ip(self) -> None:
+        scope = {
+            "type": "http",
+            "headers": [],
+            "client": ("192.168.1.1", 12345),
+        }
+        request = Request(scope)
+        assert _client_ip(request) == "192.168.1.1"
+
+    def test_no_client_returns_unknown(self) -> None:
+        scope = {"type": "http", "headers": []}
+        request = Request(scope)
+        assert _client_ip(request) == "unknown"
+
+    def test_single_ip_with_depth_1(self) -> None:
+        scope = {
+            "type": "http",
+            "headers": [(b"x-forwarded-for", b"single.ip")],
+        }
+        request = Request(scope)
+        assert _client_ip(request, depth=1) == "single.ip"
+
+
+class TestInMemoryFallback:
+    """Tests for in-memory rate limit fallback when Redis is unavailable."""
+
+    @mock.patch("api.rate_limiter._get_rate_limit_redis")
+    def test_fallback_enforces_limits_when_redis_unavailable(self, mock_get_redis: mock.MagicMock) -> None:
+        """When Redis is unavailable at startup, in-memory fallback should enforce limits."""
+        import redis as redis_lib
+        mock_get_redis.side_effect = redis_lib.RedisError("connection refused")
+
+        config = _make_config()
+        app = _build_app(config)
+        client = TestClient(app)
+
+        # Should allow first 3 requests (limit=3)
+        for i in range(3):
+            resp = client.get("/api/listing")
+            assert resp.status_code == 200, f"Request {i+1} should be allowed"
+
+        # 4th request should be rate limited
+        resp = client.get("/api/listing")
+        assert resp.status_code == 429
+
+    @mock.patch("api.rate_limiter._get_rate_limit_redis")
+    def test_fallback_activates_on_redis_error_during_request(self, mock_get_redis: mock.MagicMock) -> None:
+        """When Redis errors during request handling, fallback should activate."""
+        import redis as redis_lib
+
+        mock_redis = mock.MagicMock()
+        mock_pipe = mock.MagicMock()
+        mock_pipe.execute.side_effect = redis_lib.RedisError("connection lost")
+        mock_redis.pipeline.return_value = mock_pipe
+        mock_redis.ping.return_value = True
+        mock_get_redis.return_value = mock_redis
+
+        config = _make_config()
+        app = _build_app(config)
+        client = TestClient(app)
+
+        # First request should succeed via fallback
+        resp = client.get("/api/listing")
+        assert resp.status_code == 200
+        assert "X-RateLimit-Limit" in resp.headers
diff --git a/tests/unit/test_security_headers.py b/tests/unit/test_security_headers.py
new file mode 100644
index 0000000..1e61423
--- /dev/null
+++ b/tests/unit/test_security_headers.py
@@ -0,0 +1,56 @@
+"""Unit tests for api/security_headers.py."""
+from starlette.testclient import TestClient
+from starlette.applications import Starlette
+from starlette.requests import Request
+from starlette.responses import JSONResponse
+from starlette.routing import Route
+
+from api.security_headers import SecurityHeadersMiddleware
+
+
+async def _ok_endpoint(request: Request) -> JSONResponse:
+    return JSONResponse({"ok": True})
+
+
+def _build_app() -> Starlette:
+    app = Starlette(routes=[Route("/test", _ok_endpoint)])
+    app.add_middleware(SecurityHeadersMiddleware)
+    return app
+
+
+class TestSecurityHeaders:
+    """Tests for SecurityHeadersMiddleware."""
+
+    def test_x_content_type_options(self) -> None:
+        client = TestClient(_build_app())
+        resp = client.get("/test")
+        assert resp.headers["X-Content-Type-Options"] == "nosniff"
+
+    def test_x_frame_options(self) -> None:
+        client = TestClient(_build_app())
+        resp = client.get("/test")
+        assert resp.headers["X-Frame-Options"] == "DENY"
+
+    def test_referrer_policy(self) -> None:
+        client = TestClient(_build_app())
+        resp = client.get("/test")
+        assert resp.headers["Referrer-Policy"] == "strict-origin-when-cross-origin"
+
+    def test_content_security_policy(self) -> None:
+        client = TestClient(_build_app())
+        resp = client.get("/test")
+        assert "Content-Security-Policy" in resp.headers
+        csp = resp.headers["Content-Security-Policy"]
+        assert "default-src 'self'" in csp
+        assert "frame-ancestors 'none'" in csp
+
+    def test_hsts_set_for_https(self) -> None:
+        client = TestClient(_build_app())
+        resp = client.get("/test", headers={"x-forwarded-proto": "https"})
+        assert "Strict-Transport-Security" in resp.headers
+        assert "max-age=" in resp.headers["Strict-Transport-Security"]
+
+    def test_hsts_not_set_for_http(self) -> None:
+        client = TestClient(_build_app())
+        resp = client.get("/test")
+        assert "Strict-Transport-Security" not in resp.headers
diff --git a/tests/unit/test_task_service.py b/tests/unit/test_task_service.py
index e71d311..e121cb5 100644
--- a/tests/unit/test_task_service.py
+++ b/tests/unit/test_task_service.py
@@ -304,3 +304,84 @@ class TestClearAllTasks:
             # Should not raise despite revoke failure
             count = clear_all_tasks("test@example.com", revoke=True)
             assert count == 1
+
+
+from fastapi.testclient import TestClient
+
+
+class TestTaskStatusSecurity:
+    """Tests for task status endpoint security (IDOR, traceback suppression)."""
+
+    def _get_client(self) -> TestClient:
+        """Create test client with mocked auth."""
+        from api.app import app
+        from api.auth import get_current_user, User
+
+        mock_user = User(sub="test", email="test@example.com", name="Test")
+        app.dependency_overrides[get_current_user] = lambda: mock_user
+        client = TestClient(app, raise_server_exceptions=False)
+        return client
+
+    @patch("api.app.task_service")
+    def test_returns_404_for_unowned_task(self, mock_task_service: MagicMock) -> None:
+        mock_task_service.get_user_tasks.return_value = ["task-abc"]
+        client = self._get_client()
+        try:
+            resp = client.get("/api/task_status", params={"task_id": "task-xyz"})
+            assert resp.status_code == 404
+        finally:
+            from api.app import app
+            from api.auth import get_current_user
+            app.dependency_overrides.pop(get_current_user, None)
+
+    @patch("api.app.task_service")
+    def test_returns_200_for_owned_task(self, mock_task_service: MagicMock) -> None:
+        mock_status = MagicMock()
+        mock_status.task_id = "task-abc"
+        mock_status.status = "SUCCESS"
+        mock_status.result = None
+        mock_status.progress = None
+        mock_status.processed = None
+        mock_status.total = None
+        mock_status.message = None
+        mock_status.error = None
+        mock_status.traceback = None
+
+        mock_task_service.get_user_tasks.return_value = ["task-abc"]
+        mock_task_service.get_task_status.return_value = mock_status
+        client = self._get_client()
+        try:
+            resp = client.get("/api/task_status", params={"task_id": "task-abc"})
+            assert resp.status_code == 200
+        finally:
+            from api.app import app
+            from api.auth import get_current_user
+            app.dependency_overrides.pop(get_current_user, None)
+
+    @patch("api.app.APP_ENV", "production")
+    @patch("api.app.task_service")
+    def test_traceback_suppressed_in_production(self, mock_task_service: MagicMock) -> None:
+        mock_status = MagicMock()
+        mock_status.task_id = "task-abc"
+        mock_status.status = "FAILURE"
+        mock_status.result = None
+        mock_status.progress = None
+        mock_status.processed = None
+        mock_status.total = None
+        mock_status.message = None
+        mock_status.error = "Internal error"
+        mock_status.traceback = "Traceback (most recent call last)..."
+
+        mock_task_service.get_user_tasks.return_value = ["task-abc"]
+        mock_task_service.get_task_status.return_value = mock_status
+        client = self._get_client()
+        try:
+            resp = client.get("/api/task_status", params={"task_id": "task-abc"})
+            assert resp.status_code == 200
+            data = resp.json()
+            assert data["traceback"] is None
+            assert data["error"] is None
+        finally:
+            from api.app import app
+            from api.auth import get_current_user
+            app.dependency_overrides.pop(get_current_user, None)