feat(trx-core,trx-protocol,trx-backend-soapysdr): add spectrum data pipeline

Add SpectrumData struct (bins, center_hz, sample_rate) to RigState and
RigSnapshot. Add GetSpectrum RigCommand and ClientCommand plumbed through
the protocol layer. SoapySDR DSP pipeline now computes a 1024-bin FFT
(Hann window, FFT-shifted, dBFS) every 4 IQ blocks (~10 Hz update rate)
and exposes it via RigCat::get_spectrum(). The rig_task handles
GetSpectrum without persisting spectrum data in ongoing state.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>

src/trx-core/src/rig/command.rs

@@ -32,4 +32,5 @@ pub enum RigCommand {
     ResetWsprDecoder,
     SetBandwidth(u32),
     SetFirTaps(u32),
+    GetSpectrum,
 }

src/trx-core/src/rig/controller/handlers.rs

@@ -514,7 +514,8 @@ pub fn command_from_rig_command(cmd: RigCommand) -> Box<dyn RigCommandHandler> {
         | RigCommand::ResetFt8Decoder
         | RigCommand::ResetWsprDecoder
         | RigCommand::SetBandwidth(_)
-        | RigCommand::SetFirTaps(_) => Box::new(GetSnapshotCommand),
+        | RigCommand::SetFirTaps(_)
+        | RigCommand::GetSpectrum => Box::new(GetSnapshotCommand),
     }
 }
 

src/trx-core/src/rig/mod.rs

@@ -149,6 +149,11 @@ pub trait RigCat: Rig + Send {
     fn filter_state(&self) -> Option<state::RigFilterState> {
         None
     }
+
+    /// Return the latest spectrum frame if this backend supports spectrum output.
+    fn get_spectrum(&self) -> Option<state::SpectrumData> {
+        None
+    }
 }
 
 /// Snapshot of a rig's status that every backend can expose.

src/trx-core/src/rig/state.rs

@@ -46,6 +46,10 @@ pub struct RigState {
     /// Skipped in serde; flows into RigSnapshot via snapshot().
     #[serde(skip)]
     pub filter: Option<RigFilterState>,
+    /// Latest spectrum frame from SDR backends.
+    /// Skipped in serde (not part of persistent state); flows into RigSnapshot on demand.
+    #[serde(skip)]
+    pub spectrum: Option<SpectrumData>,
     #[serde(default, skip_serializing)]
     pub aprs_decode_reset_seq: u64,
     #[serde(default, skip_serializing)]
@@ -132,6 +136,7 @@ impl RigState {
             cw_wpm: 15,
             cw_tone_hz: 700,
             filter: None,
+            spectrum: None,
             aprs_decode_reset_seq: 0,
             cw_decode_reset_seq: 0,
             ft8_decode_reset_seq: 0,
@@ -192,6 +197,7 @@ impl RigState {
             ft8_decode_enabled: snapshot.ft8_decode_enabled,
             wspr_decode_enabled: snapshot.wspr_decode_enabled,
             filter: snapshot.filter,
+            spectrum: None, // spectrum flows through /api/spectrum, not persistent state
             aprs_decode_reset_seq: 0,
             cw_decode_reset_seq: 0,
             ft8_decode_reset_seq: 0,
@@ -230,6 +236,7 @@ impl RigState {
             ft8_decode_enabled: self.ft8_decode_enabled,
             wspr_decode_enabled: self.wspr_decode_enabled,
             filter: self.filter.clone(),
+            spectrum: self.spectrum.clone(),
         })
     }
 
@@ -264,6 +271,17 @@ pub struct RigFilterState {
     pub cw_center_hz: u32,
 }
 
+/// Spectrum data from SDR backends (FFT magnitude over the full capture bandwidth).
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct SpectrumData {
+    /// FFT magnitude bins in dBFS, FFT-shifted so DC (centre frequency) is at index N/2.
+    pub bins: Vec<f32>,
+    /// Centre frequency of the SDR capture in Hz.
+    pub center_hz: u64,
+    /// SDR capture sample rate in Hz; the displayed span is ±sample_rate/2.
+    pub sample_rate: u32,
+}
+
 /// Read-only projection of state shared with clients.
 #[derive(Debug, Clone, Serialize, Deserialize)]
 pub struct RigSnapshot {
@@ -300,4 +318,6 @@ pub struct RigSnapshot {
     pub cw_tone_hz: u32,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub filter: Option<RigFilterState>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub spectrum: Option<SpectrumData>,
 }