fix(config): warn on unknown config keys instead of silently dropping them

_dict_to_dataclass() silently continue'd past any key not in the target
dataclass's field set -- an operator could set a config key, restart, and
have it vanish with zero feedback (config.example.yaml's phantom
mesh_intelligence keys are exactly this bug, fixed separately).

Now logs a WARNING naming the key and the dataclass, hinting at a typo or
a renamed/removed field, via the module's existing _config_logger.

Traced every dynamic/free-form config path to rule out false positives:
notifications.toggles, notifications.destinations, generic_sources,
mesh_sources, and notifications.rules all route through explicit
dict-of-dataclass or verbatim-passthrough handling and never spuriously
warn. Two legitimate legacy shapes DO hit the strict field-check path with
keys that were never (and will never be) dataclass fields:

- notifications.channels (pre-v0.5 channel list), consumed directly from
  the raw dict by _migrate_legacy_channels
- notifications.region_routes.enabled (pre mt/mc-split master switch),
  read directly by the explicit region_routes handler

Both are allowlisted in _KNOWN_LEGACY_DROP_KEYS so users mid-migration
don't get spurious noise on every load.

Added tests/test_config_loader.py coverage: unknown key warns and does
not raise, both legacy shapes stay silent, and the free-form/dynamic
sections never warn for keys valid on their real target shape.

work/meshai/config.py

@@ -1241,6 +1241,29 @@ def _migrate_legacy_channels(notifications, data: dict):
         _config_logger.info("Migrated to %d self-contained rules", len(notifications.rules))
 
 
+# Keys that are legitimately present in raw config dicts but intentionally have
+# NO matching dataclass field on the target class -- they're consumed by
+# special-case logic elsewhere in _dict_to_dataclass (e.g. legacy-format
+# migration) rather than becoming a field. Warning about these would be a
+# false positive: the key isn't a typo, it's a known, still-supported legacy
+# shape. Keyed by (dataclass, key name).
+_KNOWN_LEGACY_DROP_KEYS = {
+    # Pre-v0.5 notifications.channels list; migrated into self-contained
+    # rules by _migrate_legacy_channels (reads straight from the raw dict,
+    # not from the coerced NotificationsConfig).
+    (NotificationsConfig, "channels"): (
+        "legacy notifications.channels format, handled by _migrate_legacy_channels"
+    ),
+    # Pre-region-routing-split master switch. The explicit region_routes
+    # handler (in the "notifications" branch below) reads this directly via
+    # rr.get("enabled", ...) as the default for mt_enabled; it never becomes
+    # a RegionRouteMatrix field.
+    (RegionRouteMatrix, "enabled"): (
+        "legacy region_routes.enabled (pre-mt/mc split), mapped to mt_enabled"
+    ),
+}
+
+
 def _dict_to_dataclass(cls, data: dict):
     """Recursively convert dict to dataclass, handling nested structures."""
     if data is None:
@@ -1253,6 +1276,13 @@ def _dict_to_dataclass(cls, data: dict):
         if key.startswith("_"):
             continue
         if key not in field_types:
+            if (cls, key) not in _KNOWN_LEGACY_DROP_KEYS:
+                _config_logger.warning(
+                    "Config key '%s' is not a recognized field on %s -- it will "
+                    "be IGNORED (dropped) on load. Check for a typo, or a "
+                    "renamed/removed field.",
+                    key, cls.__name__,
+                )
             continue
 
         field_type = field_types[key]

work/tests/test_config_loader.py

@@ -6,10 +6,14 @@ cfg.notifications.rules as raw dicts (which crashed Dispatcher._matching_rules
 on rule.enabled). config_loader.load_config uses this same _dict_to_dataclass.
 """
 
+import logging
+
 from meshai.config import (
     Config,
+    MeshIntelligenceConfig,
     NotificationRuleConfig,
     NotificationToggle,
+    RegionRouteMatrix,
     _dataclass_to_dict,
     _dict_to_dataclass,
 )
@@ -84,3 +88,88 @@ def test_toggle_meshcore_channel_name_round_trips():
     # Default stays None when unset.
     default = _dict_to_dataclass(NotificationToggle, {"name": "weather"})
     assert default.meshcore_channel is None
+
+
+def test_unknown_key_warns_but_does_not_raise(caplog):
+    """An unrecognized config key (typo, or a renamed/removed field) logs a
+    WARNING naming the key and the dataclass, and the key is silently dropped
+    (never raises). Regression guard for the silent-drop bug: previously an
+    operator could set a bogus/typo'd key, restart, and get zero feedback."""
+    data = {
+        "mesh_intelligence": {
+            "enabled": True,
+            "region_radius_miles": 40.0,  # never a real field -- see config.example.yaml fix
+        }
+    }
+    with caplog.at_level(logging.WARNING, logger="meshai.config"):
+        cfg = _dict_to_dataclass(Config, data)
+
+    assert cfg.mesh_intelligence.enabled is True
+    assert not hasattr(cfg.mesh_intelligence, "region_radius_miles")
+    warnings = [r for r in caplog.records if r.levelno == logging.WARNING]
+    assert len(warnings) == 1
+    msg = warnings[0].getMessage()
+    assert "region_radius_miles" in msg
+    assert "MeshIntelligenceConfig" in msg
+
+
+def test_legacy_region_routes_enabled_does_not_warn(caplog):
+    """region_routes.enabled is a pre-mt/mc-split legacy key, still read
+    directly by the explicit region_routes handler in _dict_to_dataclass.
+    It intentionally has no RegionRouteMatrix field and must NOT warn --
+    warning here would be a false positive for every config still using the
+    pre-split single master switch."""
+    data = {"notifications": {"region_routes": {"enabled": True, "cells": {}}}}
+    with caplog.at_level(logging.WARNING, logger="meshai.config"):
+        cfg = _dict_to_dataclass(Config, data)
+
+    assert cfg.notifications.region_routes.mt_enabled is True
+    assert not any(
+        "region_routes" in r.getMessage() or "'enabled'" in r.getMessage()
+        for r in caplog.records
+    )
+
+
+def test_legacy_notifications_channels_does_not_warn(caplog):
+    """notifications.channels (pre-v0.5 format) has no NotificationsConfig
+    field -- it's consumed directly from the raw dict by
+    _migrate_legacy_channels. Must not warn for users mid-migration."""
+    data = {
+        "notifications": {
+            "channels": [{"id": "c1", "type": "mesh_broadcast", "channel_index": 0}],
+            "rules": [{"name": "r1", "channel_ids": ["c1"], "categories": ["fire"]}],
+        }
+    }
+    with caplog.at_level(logging.WARNING, logger="meshai.config"):
+        cfg = _dict_to_dataclass(Config, data)
+
+    assert len(cfg.notifications.rules) == 1
+    assert cfg.notifications.rules[0].broadcast_channel == 0
+    assert not any("channels" in r.getMessage() for r in caplog.records)
+
+
+def test_dynamic_sections_do_not_warn(caplog):
+    """Sections that are intentionally free-form/passthrough (generic_sources)
+    or use explicit dict-of-dataclass coercion (toggles, destinations) must
+    never warn for keys that ARE valid on their actual target shape."""
+    data = {
+        "notifications": {
+            "toggles": {
+                "weather": {"name": "weather", "enabled": True, "min_severity": "priority"},
+            },
+            "destinations": {
+                "d1": {"name": "d1", "type": "mesh_broadcast", "broadcast_channel": 0},
+            },
+        },
+        "mesh_sources": [
+            {"name": "mv", "type": "meshview", "url": "http://x", "enabled": True},
+        ],
+        "generic_sources": [
+            {"name": "gs1", "enabled": True, "url": "http://x", "not_a_dataclass_field": "fine"},
+        ],
+    }
+    with caplog.at_level(logging.WARNING, logger="meshai.config"):
+        cfg = _dict_to_dataclass(Config, data)
+
+    assert caplog.records == []
+    assert cfg.generic_sources[0]["not_a_dataclass_field"] == "fine"