refactor(message_handler): DMs read SNR and RSSI through _message_signal

handle_contact_message's copy of the payload/metadata/signal-cache lookup becomes a _message_signal call with its own SNR keys (it also accepts signal_to_noise and signal_noise_ratio), so DMs and channel messages share one implementation. The helper loses a comment that only made sense inline.

A DM replay (1,500 corpus packets as RF rows, 1,500 DMs with varied SNR/RSSI key layouts, metadata, cached signal values keyed by pubkey prefix, with and without radio contacts) gives byte-identical processed messages and logger calls; passing the channel keys instead changes them. The channel replay is unchanged.

modules/channel_message.py

@@ -78,7 +78,6 @@ class ChannelMessageMixin:
         self, payload: dict[str, Any], metadata: dict[str, Any] | None, snr_payload_keys: tuple[str, ...]
     ) -> tuple[float | None, int | None]:
         """A message's SNR and RSSI from its payload or metadata, else the signal cache by pubkey prefix."""
-        # Get SNR and RSSI using the same logic as contact messages
         snr: float | None = None
         rssi: int | None = None
 

modules/message_handler.py

@@ -283,28 +283,9 @@ class MessageHandler(MeshGraphRecorderMixin, ContactEventsMixin, RfCorrelationMi
                 self._log_dm_routing_from_rf(message_pubkey)
 
             # Get additional metadata - try multiple sources for SNR and RSSI
-            snr: float | None = None
-            rssi: int | None = None
-
-            # Try to get SNR from payload first - check multiple possible field names
-            snr = _signal_value(payload, metadata, ("SNR", "snr", "signal_to_noise", "signal_noise_ratio"), ("snr", "SNR"), float)
-
-            # If still no SNR, try to get it from the cache using pubkey prefix from payload
-            if snr is None:
-                pubkey_prefix = payload.get("pubkey_prefix", "")
-                if pubkey_prefix and pubkey_prefix in self.snr_cache:
-                    snr = self.snr_cache[pubkey_prefix]
-                    self.logger.debug(f"Retrieved cached SNR {snr} for pubkey {pubkey_prefix}")
-
-            # Try to get RSSI from payload first
-            rssi = _signal_value(payload, metadata, ("RSSI", "rssi", "signal_strength"), ("rssi", "RSSI"), int)
-
-            # If still no RSSI, try to get it from the cache using pubkey prefix from payload
-            if rssi is None:
-                pubkey_prefix = payload.get("pubkey_prefix", "")
-                if pubkey_prefix and pubkey_prefix in self.rssi_cache:
-                    rssi = int(self.rssi_cache[pubkey_prefix])
-                    self.logger.debug(f"Retrieved cached RSSI {rssi} for pubkey {pubkey_prefix}")
+            snr, rssi = self._message_signal(
+                payload, metadata, ("SNR", "snr", "signal_to_noise", "signal_noise_ratio")
+            )
 
             # For DMs, we can't decode the encrypted packet, but we can get SNR/RSSI from the payload
             # For channel messages, we can decode the packet since they use shared keys