[feat](trx-protocol): add SubscribeMeter command and MeterUpdate DTO

Adds a dedicated one-way JSON-line stream for high-rate signal-strength
samples so meter updates bypass full-RigState diffing in the control path.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-protocol/src/lib.rs

@@ -18,4 +18,4 @@ pub use auth::{NoAuthValidator, SimpleTokenValidator, TokenValidator};
 pub use codec::{mode_to_string, parse_envelope, parse_mode};
 pub use decoders::{DecoderActivation, DecoderDescriptor, DECODER_REGISTRY};
 pub use mapping::{client_command_to_rig, rig_command_to_client};
-pub use types::{ClientCommand, ClientEnvelope, ClientResponse, RigEntry};
+pub use types::{ClientCommand, ClientEnvelope, ClientResponse, MeterUpdate, RigEntry};

src/trx-protocol/src/mapping.rs

@@ -102,7 +102,7 @@ macro_rules! define_command_mapping {
 
 define_command_mapping! {
     // ── Client-only variants (no RigCommand counterpart) ─────────────
-    client_only: GetRigs, GetSatPasses;
+    client_only: GetRigs, GetSatPasses, SubscribeMeter;
 
     // ── Unit variants (no payload) ───────────────────────────────────
     unit:

src/trx-protocol/src/types.rs

@@ -61,6 +61,24 @@ pub enum ClientCommand {
     SetSamCarrierSync { enabled: bool },
     SetRecorderEnabled { enabled: bool },
     GetSpectrum,
+    /// Subscribe to a per-rig meter stream on this connection.  After the
+    /// server receives this command, the connection becomes a one-way flow of
+    /// newline-delimited `MeterUpdate` JSON frames and no further commands or
+    /// regular responses are sent.  Intended for a dedicated TCP connection.
+    SubscribeMeter,
+}
+
+/// Fast meter sample pushed by the server on a dedicated meter stream.
+///
+/// Emitted at ~30 Hz for SDR backends and ~6–7 Hz for CAT backends.
+#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
+pub struct MeterUpdate {
+    /// Rig identifier this sample belongs to.
+    pub rig_id: String,
+    /// Receive signal strength in dBm (rig/DSP-reported).
+    pub sig_dbm: f64,
+    /// Monotonic millisecond timestamp from the server's steady clock.
+    pub ts_ms: u64,
 }
 
 /// Envelope for client commands with optional authentication token and rig routing.