fix: add _validate_gateway_config tests and API_SERVER_KEY network binding warning

Refs #892 - Gateway config debt: missing keys and broken fallbacks

Changes:
- Add `_is_network_accessible()` helper to gateway/config.py (avoids circular
  import with gateway.platforms.base which imports from gateway.config)
- Add API_SERVER_KEY warning in `_validate_gateway_config`: when the API server
  is enabled on a network-accessible address (0.0.0.0, public IP, hostname) but
  no key is configured, log a warning at config-load time so operators see the
  issue before any adapter initialisation runs
- Add `TestValidateGatewayConfig` in tests/gateway/test_config.py covering:
  - idle_minutes <= 0 and None are corrected to 1440 (default)
  - at_hour outside 0-23 is corrected to 4 (default)
  - Boundary hours 0 and 23 are accepted unchanged
  - Empty platform token triggers a warning log
  - Disabled platform with empty token produces no warning
  - API server on 0.0.0.0 without key logs a warning
  - API server on 127.0.0.1 without key is silent (loopback is allowed)
  - API server with a key set logs no warning regardless of bind address

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

gateway/config.py

@@ -8,6 +8,7 @@ Handles loading and validating configuration for:
 - Delivery preferences
 """
 
+import ipaddress
 import logging
 import os
 import json
@@ -679,6 +680,26 @@ def load_gateway_config() -> GatewayConfig:
     return config
 
 
+def _is_network_accessible(host: str) -> bool:
+    """Return True if *host* would expose a server beyond the loopback interface.
+
+    Duplicates the logic in ``gateway.platforms.base.is_network_accessible``
+    without creating a circular import (base.py imports from this module).
+    """
+    try:
+        addr = ipaddress.ip_address(host)
+        if addr.is_loopback:
+            return False
+        # ::ffff:127.x.x.x — Python's is_loopback returns False for
+        # IPv4-mapped loopback; unwrap and check the underlying IPv4.
+        if getattr(addr, "ipv4_mapped", None) and addr.ipv4_mapped.is_loopback:
+            return False
+        return True
+    except ValueError:
+        # Hostname: assume it could be network-accessible.
+        return True
+
+
 def _validate_gateway_config(config: "GatewayConfig") -> None:
     """Validate and sanitize a loaded GatewayConfig in place.
 
@@ -747,6 +768,22 @@ def _validate_gateway_config(config: "GatewayConfig") -> None:
                 )
                 pconfig.enabled = False
 
+    # Warn when the API server is enabled on a network-accessible address
+    # without an auth key.  The adapter will refuse to start anyway, but
+    # surfacing this at config-load time lets operators see the problem in
+    # the startup log before any platform adapter initialisation runs.
+    api_cfg = config.platforms.get(Platform.API_SERVER)
+    if api_cfg and api_cfg.enabled:
+        key = api_cfg.extra.get("key", "")
+        host = api_cfg.extra.get("host", "127.0.0.1")
+        if not key and _is_network_accessible(host):
+            logger.warning(
+                "API Server is enabled on %s but API_SERVER_KEY is not set. "
+                "The adapter will refuse to start on a network-accessible address. "
+                "Set API_SERVER_KEY or bind to 127.0.0.1 for local-only access.",
+                host,
+            )
+
 
 def _apply_env_overrides(config: GatewayConfig) -> None:
     """Apply environment variable overrides to config."""

tests/gateway/test_config.py

@@ -10,6 +10,7 @@ from gateway.config import (
     PlatformConfig,
     SessionResetPolicy,
     _apply_env_overrides,
+    _validate_gateway_config,
     load_gateway_config,
 )
 
@@ -294,3 +295,151 @@ class TestHomeChannelEnvOverrides:
             home = config.platforms[platform].home_channel
             assert home is not None, f"{platform.value}: home_channel should not be None"
             assert (home.chat_id, home.name) == expected, platform.value
+
+
+class TestValidateGatewayConfig:
+    """Tests for _validate_gateway_config — in-place sanitisation of loaded config."""
+
+    # -- idle_minutes validation --
+
+    def test_idle_minutes_zero_is_corrected_to_default(self):
+        config = GatewayConfig()
+        config.default_reset_policy.idle_minutes = 0
+        _validate_gateway_config(config)
+        assert config.default_reset_policy.idle_minutes == 1440
+
+    def test_idle_minutes_negative_is_corrected_to_default(self):
+        config = GatewayConfig()
+        config.default_reset_policy.idle_minutes = -60
+        _validate_gateway_config(config)
+        assert config.default_reset_policy.idle_minutes == 1440
+
+    def test_idle_minutes_none_is_corrected_to_default(self):
+        config = GatewayConfig()
+        config.default_reset_policy.idle_minutes = None  # type: ignore[assignment]
+        _validate_gateway_config(config)
+        assert config.default_reset_policy.idle_minutes == 1440
+
+    def test_valid_idle_minutes_is_unchanged(self):
+        config = GatewayConfig()
+        config.default_reset_policy.idle_minutes = 90
+        _validate_gateway_config(config)
+        assert config.default_reset_policy.idle_minutes == 90
+
+    # -- at_hour validation --
+
+    def test_at_hour_too_high_is_corrected_to_default(self):
+        config = GatewayConfig()
+        config.default_reset_policy.at_hour = 24
+        _validate_gateway_config(config)
+        assert config.default_reset_policy.at_hour == 4
+
+    def test_at_hour_negative_is_corrected_to_default(self):
+        config = GatewayConfig()
+        config.default_reset_policy.at_hour = -1
+        _validate_gateway_config(config)
+        assert config.default_reset_policy.at_hour == 4
+
+    def test_valid_at_hour_is_unchanged(self):
+        config = GatewayConfig()
+        config.default_reset_policy.at_hour = 3
+        _validate_gateway_config(config)
+        assert config.default_reset_policy.at_hour == 3
+
+    def test_at_hour_boundary_values_are_valid(self):
+        for valid_hour in (0, 23):
+            config = GatewayConfig()
+            config.default_reset_policy.at_hour = valid_hour
+            _validate_gateway_config(config)
+            assert config.default_reset_policy.at_hour == valid_hour
+
+    # -- empty-token warning (enabled platforms) --
+
+    def test_empty_string_token_logs_warning(self, caplog):
+        import logging
+        config = GatewayConfig(
+            platforms={
+                Platform.TELEGRAM: PlatformConfig(enabled=True, token=""),
+            }
+        )
+        with caplog.at_level(logging.WARNING, logger="gateway.config"):
+            _validate_gateway_config(config)
+        assert any(
+            "TELEGRAM_BOT_TOKEN" in r.message and "empty" in r.message
+            for r in caplog.records
+        )
+
+    def test_disabled_platform_with_empty_token_no_warning(self, caplog):
+        import logging
+        config = GatewayConfig(
+            platforms={
+                Platform.TELEGRAM: PlatformConfig(enabled=False, token=""),
+            }
+        )
+        with caplog.at_level(logging.WARNING, logger="gateway.config"):
+            _validate_gateway_config(config)
+        assert not any("TELEGRAM_BOT_TOKEN" in r.message for r in caplog.records)
+
+    # -- API Server key / binding warnings --
+
+    def test_api_server_network_binding_without_key_logs_warning(self, caplog):
+        import logging
+        config = GatewayConfig(
+            platforms={
+                Platform.API_SERVER: PlatformConfig(
+                    enabled=True,
+                    extra={"host": "0.0.0.0"},
+                ),
+            }
+        )
+        with caplog.at_level(logging.WARNING, logger="gateway.config"):
+            _validate_gateway_config(config)
+        assert any(
+            "API_SERVER_KEY" in r.message for r in caplog.records
+        )
+
+    def test_api_server_loopback_without_key_no_warning(self, caplog):
+        import logging
+        config = GatewayConfig(
+            platforms={
+                Platform.API_SERVER: PlatformConfig(
+                    enabled=True,
+                    extra={"host": "127.0.0.1"},
+                ),
+            }
+        )
+        with caplog.at_level(logging.WARNING, logger="gateway.config"):
+            _validate_gateway_config(config)
+        assert not any(
+            "API_SERVER_KEY" in r.message for r in caplog.records
+        )
+
+    def test_api_server_network_binding_with_key_no_warning(self, caplog):
+        import logging
+        config = GatewayConfig(
+            platforms={
+                Platform.API_SERVER: PlatformConfig(
+                    enabled=True,
+                    extra={"host": "0.0.0.0", "key": "sk-real-key-here"},
+                ),
+            }
+        )
+        with caplog.at_level(logging.WARNING, logger="gateway.config"):
+            _validate_gateway_config(config)
+        assert not any(
+            "API_SERVER_KEY" in r.message for r in caplog.records
+        )
+
+    def test_api_server_default_loopback_without_key_no_warning(self, caplog):
+        """API server with no explicit host defaults to 127.0.0.1 — no warning."""
+        import logging
+        config = GatewayConfig(
+            platforms={
+                Platform.API_SERVER: PlatformConfig(enabled=True),
+            }
+        )
+        with caplog.at_level(logging.WARNING, logger="gateway.config"):
+            _validate_gateway_config(config)
+        assert not any(
+            "API_SERVER_KEY" in r.message for r in caplog.records
+        )