From e6dbfd1edb1db84929f0ad350e7703c05801682d Mon Sep 17 00:00:00 2001
From: Stan Grams <sjg@haxx.space>
Date: Mon, 30 Mar 2026 20:47:12 +0200
Subject: [PATCH] [feat](trx-protocol): add centralised decoder registry

Add DECODER_REGISTRY in trx-protocol::decoders as the single source of
truth for all decoder metadata (activation mode, supported rig modes,
background-decode capability). Replace duplicated resolver functions in
background_decode.rs and sse.rs with shared resolve_bookmark_decoders().
Add GET /decoders endpoint to expose the registry to the frontend.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Stan Grams <sjg@haxx.space>
---
 docs/Decoder_Consolidation.md                 | 365 ++++++++++++++++++
 .../trx-frontend-http/assets/web/app.js       |  18 +-
 .../trx-frontend-http/assets/web/index.html   |  11 +-
 .../assets/web/plugins/aprs.js                |   3 +-
 .../assets/web/plugins/background-decode.js   |   2 +-
 .../assets/web/plugins/bookmarks.js           |   4 +-
 .../trx-frontend-http/src/api/decoder.rs      |   9 +
 .../trx-frontend-http/src/api/mod.rs          |   1 +
 .../trx-frontend-http/src/api/sse.rs          |  29 +-
 .../src/background_decode.rs                  |  32 +-
 .../trx-frontend-http/src/scheduler.rs        |   3 +-
 .../trx-frontend-http/src/vchan.rs            |  14 +-
 src/trx-protocol/src/decoders.rs              | 250 ++++++++++++
 src/trx-protocol/src/lib.rs                   |   2 +
 src/trx-server/src/audio.rs                   |  18 +-
 .../trx-backend-soapysdr/src/lib.rs           |   5 +-
 .../trx-backend-soapysdr/src/vchan_impl.rs    |   2 +-
 17 files changed, 677 insertions(+), 91 deletions(-)
 create mode 100644 docs/Decoder_Consolidation.md
 create mode 100644 src/trx-protocol/src/decoders.rs

diff --git a/docs/Decoder_Consolidation.md b/docs/Decoder_Consolidation.md
new file mode 100644
index 0000000..a5e0357
--- /dev/null
+++ b/docs/Decoder_Consolidation.md
@@ -0,0 +1,365 @@
+# Decoder Registry Consolidation Plan
+
+**Status:** Proposed
+**Target crate:** `trx-protocol`
+
+## Problem
+
+The set of supported decoders and their mode/activation semantics is defined
+independently in 4+ locations with no single source of truth.  Adding a new
+decoder requires touching every copy; the copies are already out of sync.
+
+### Duplicate definitions today
+
+| Location | What it defines | Drift |
+|----------|----------------|-------|
+| `background_decode.rs` `SUPPORTED_DECODER_KINDS` | `["aprs","ais","ft8","ft4","ft2","wspr","hf-aprs"]` | Missing `lrpt` |
+| `background_decode.rs` `bookmark_supported_decoder_kinds()` | Mode fallback: `AIS→ais`, `PKT→aprs` | — |
+| `sse.rs` `bookmark_decoder_kinds()` | Same mode fallback, duplicated | — |
+| `background-decode.js` `SUPPORTED_DECODERS` | `["aprs","ais","ft8","wspr","hf-aprs"]` | Missing `ft4`, `ft2`, `lrpt` |
+| `background-decode.js` `bookmarkDecoderKinds()` | Mode fallback: `AIS→ais`, `PKT→aprs` | — |
+| `bookmarks.js` `bmReadDecoders()` / `bmWriteDecoders()` | 8 hardcoded checkbox IDs | — |
+| `app.js` `_decoderToggles` | 6 hardcoded toggle button entries | — |
+| `app.js` `setModeBoundDecodeStatus()` calls | Hardcoded mode→decoder pairs | — |
+| `app.js` `bmApply()` | Gates decoder toggles on `mode === "DIG" \|\| mode === "FM"` | — |
+
+### Implicit categories
+
+Two activation patterns exist but are never formalised:
+
+- **Mode-bound** — always active when the rig is in the matching mode (AIS,
+  APRS/PKT, CW, VDES, RDS).  No user toggle.
+- **Toggle-gated** — user explicitly enables/disables; only meaningful in
+  certain modes (FT8, FT4, FT2, WSPR, HF-APRS, LRPT).
+
+---
+
+## Design
+
+### 1. Decoder registry in `trx-protocol`
+
+Add `src/trx-protocol/src/decoders.rs`:
+
+```rust
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum DecoderActivation {
+    /// Automatically active when the rig mode matches.
+    ModeBound,
+    /// User-controlled toggle; only runs in `active_modes`.
+    Toggle,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct DecoderDescriptor {
+    /// Machine identifier, e.g. `"ft8"`, `"aprs"`.
+    pub id: &'static str,
+    /// Human-readable label, e.g. `"FT8"`, `"APRS"`.
+    pub label: &'static str,
+    /// How the decoder is activated.
+    pub activation: DecoderActivation,
+    /// Rig modes where this decoder operates (upper-case).
+    pub active_modes: &'static [&'static str],
+    /// Whether the decoder can run on SDR virtual channels
+    /// (background-decode / scheduler).
+    pub background_decode: bool,
+    /// Whether this decoder should appear in bookmark forms.
+    pub bookmark_selectable: bool,
+}
+
+pub const DECODER_REGISTRY: &[DecoderDescriptor] = &[
+    DecoderDescriptor {
+        id: "ais",
+        label: "AIS",
+        activation: DecoderActivation::ModeBound,
+        active_modes: &["AIS"],
+        background_decode: true,
+        bookmark_selectable: true,
+    },
+    DecoderDescriptor {
+        id: "aprs",
+        label: "APRS",
+        activation: DecoderActivation::ModeBound,
+        active_modes: &["PKT"],
+        background_decode: true,
+        bookmark_selectable: true,
+    },
+    DecoderDescriptor {
+        id: "vdes",
+        label: "VDES",
+        activation: DecoderActivation::ModeBound,
+        active_modes: &["VDES"],
+        background_decode: false,
+        bookmark_selectable: false,
+    },
+    DecoderDescriptor {
+        id: "cw",
+        label: "CW",
+        activation: DecoderActivation::ModeBound,
+        active_modes: &["CW", "CWR"],
+        background_decode: false,
+        bookmark_selectable: false,
+    },
+    DecoderDescriptor {
+        id: "ft8",
+        label: "FT8",
+        activation: DecoderActivation::Toggle,
+        active_modes: &["DIG", "USB"],
+        background_decode: true,
+        bookmark_selectable: true,
+    },
+    DecoderDescriptor {
+        id: "ft4",
+        label: "FT4",
+        activation: DecoderActivation::Toggle,
+        active_modes: &["DIG", "USB"],
+        background_decode: true,
+        bookmark_selectable: true,
+    },
+    DecoderDescriptor {
+        id: "ft2",
+        label: "FT2",
+        activation: DecoderActivation::Toggle,
+        active_modes: &["DIG", "USB"],
+        background_decode: true,
+        bookmark_selectable: true,
+    },
+    DecoderDescriptor {
+        id: "wspr",
+        label: "WSPR",
+        activation: DecoderActivation::Toggle,
+        active_modes: &["DIG", "USB"],
+        background_decode: true,
+        bookmark_selectable: true,
+    },
+    DecoderDescriptor {
+        id: "hf-aprs",
+        label: "HF APRS",
+        activation: DecoderActivation::Toggle,
+        active_modes: &["DIG", "USB"],
+        background_decode: true,
+        bookmark_selectable: true,
+    },
+    DecoderDescriptor {
+        id: "lrpt",
+        label: "Meteor LRPT",
+        activation: DecoderActivation::Toggle,
+        active_modes: &["DIG", "USB"],
+        background_decode: false,
+        bookmark_selectable: true,
+    },
+];
+```
+
+Re-export from `trx-protocol/src/lib.rs`:
+
+```rust
+pub mod decoders;
+pub use decoders::{DecoderActivation, DecoderDescriptor, DECODER_REGISTRY};
+```
+
+### 2. Shared resolver functions in `trx-protocol::decoders`
+
+Replace all duplicated bookmark→decoder resolution with shared helpers:
+
+```rust
+/// Return decoder IDs supported for background-decode / virtual channels.
+pub fn background_decoder_ids() -> impl Iterator<Item = &'static str> {
+    DECODER_REGISTRY.iter()
+        .filter(|d| d.background_decode)
+        .map(|d| d.id)
+}
+
+/// Resolve a bookmark's effective decoder kinds.
+///
+/// If the bookmark has explicit `decoders`, filter to supported IDs.
+/// Otherwise, infer from mode using mode-bound entries in the registry.
+pub fn resolve_bookmark_decoders(
+    explicit_decoders: &[String],
+    mode: &str,
+    background_only: bool,
+) -> Vec<String> {
+    let supported: Vec<&DecoderDescriptor> = DECODER_REGISTRY.iter()
+        .filter(|d| !background_only || d.background_decode)
+        .collect();
+
+    // Explicit decoders take priority.
+    let from_explicit: Vec<String> = explicit_decoders.iter()
+        .map(|s| s.trim().to_ascii_lowercase())
+        .filter(|s| supported.iter().any(|d| d.id == s.as_str()))
+        .collect();
+    if !from_explicit.is_empty() {
+        return dedup(from_explicit);
+    }
+
+    // Fall back: infer from mode via mode-bound decoders.
+    let mode_upper = mode.trim().to_ascii_uppercase();
+    supported.iter()
+        .filter(|d| d.activation == DecoderActivation::ModeBound
+                  && d.active_modes.contains(&mode_upper.as_str()))
+        .map(|d| d.id.to_string())
+        .collect()
+}
+```
+
+### 3. REST endpoint `/decoders`
+
+Add a `GET /decoders` handler in `trx-frontend-http` that serialises
+`DECODER_REGISTRY` as JSON.  The frontend fetches this once on page load
+and uses it to drive all decoder-related UI.
+
+### 4. Delete duplicated Rust code
+
+| File | Delete |
+|------|--------|
+| `background_decode.rs` | `SUPPORTED_DECODER_KINDS`, `supported_decoder_kinds()`, `bookmark_supported_decoder_kinds()` |
+| `sse.rs` | `bookmark_decoder_kinds()` |
+
+Replace call sites with `trx_protocol::decoders::resolve_bookmark_decoders()`.
+
+### 5. Refactor JS to consume the registry
+
+#### `bookmarks.js`
+
+Replace `bmReadDecoders()` / `bmWriteDecoders()` with data-driven functions:
+
+```js
+// Populated from GET /decoders on page load.
+let decoderRegistry = [];
+
+function bmReadDecoders() {
+  return decoderRegistry
+    .filter(d => d.bookmark_selectable)
+    .filter(d => document.getElementById("bm-dec-" + d.id)?.checked)
+    .map(d => d.id);
+}
+
+function bmWriteDecoders(list) {
+  const set = new Set(list || []);
+  decoderRegistry
+    .filter(d => d.bookmark_selectable)
+    .forEach(d => {
+      const el = document.getElementById("bm-dec-" + d.id);
+      if (el) el.checked = set.has(d.id);
+    });
+}
+```
+
+Generate the checkbox HTML from the registry instead of hardcoding 8 inputs.
+
+#### `bmApply()` in `bookmarks.js`
+
+Replace the `mode === "DIG" || mode === "FM"` gate:
+
+```js
+const hasDecoders = Array.isArray(bm.decoders) && bm.decoders.length > 0;
+const toggleDecoders = decoderRegistry.filter(d => d.activation === "toggle");
+const shouldToggle = hasDecoders && toggleDecoders.some(d =>
+  d.active_modes.includes(bm.mode.toUpperCase())
+);
+```
+
+#### `background-decode.js`
+
+Delete `SUPPORTED_DECODERS` constant and `bookmarkDecoderKinds()`.  Replace
+with the shared registry:
+
+```js
+function bookmarkDecoderKinds(bookmark) {
+  // Use the same resolution logic as the backend, driven by the registry.
+  const explicit = (bookmark.decoders || [])
+    .map(s => s.trim().toLowerCase())
+    .filter(s => decoderRegistry.some(d => d.background_decode && d.id === s));
+  if (explicit.length > 0) return explicit;
+  const mode = (bookmark.mode || "").toUpperCase();
+  return decoderRegistry
+    .filter(d => d.activation === "mode_bound"
+              && d.background_decode
+              && d.active_modes.includes(mode))
+    .map(d => d.id);
+}
+```
+
+#### `app.js` — decoder toggle buttons
+
+Replace the hardcoded `_decoderToggles` object and `syncDecoderToggle()` loop.
+Generate toggle buttons from `decoderRegistry.filter(d => d.activation === "toggle")`.
+
+#### `app.js` — `setModeBoundDecodeStatus()`
+
+Drive the calls from the registry instead of hardcoded mode arrays:
+
+```js
+decoderRegistry
+  .filter(d => d.activation === "mode_bound")
+  .forEach(d => {
+    const el = document.getElementById(d.id + "-status");
+    setModeBoundDecodeStatus(el, d.active_modes, ...);
+  });
+```
+
+#### `app.js` — FT8/WSPR status gating
+
+Replace `modeUpper !== "DIG" && modeUpper !== "USB"` with a registry lookup:
+
+```js
+const ft8Desc = decoderRegistry.find(d => d.id === "ft8");
+if (ft8Desc && !ft8Desc.active_modes.includes(modeUpper)) { ... }
+```
+
+### 6. Generate bookmark form decoder checkboxes
+
+The HTML currently has 8 hardcoded `<label><input id="bm-dec-ft8" ...>` blocks.
+Replace with a `<div id="bm-decoder-checkboxes"></div>` container populated on
+load from the registry:
+
+```js
+function bmBuildDecoderCheckboxes() {
+  const container = document.getElementById("bm-decoder-checkboxes");
+  if (!container) return;
+  container.innerHTML = "";
+  decoderRegistry
+    .filter(d => d.bookmark_selectable)
+    .forEach(d => {
+      const label = document.createElement("label");
+      label.innerHTML = `<input type="checkbox" id="bm-dec-${d.id}" /> ${d.label}`;
+      container.appendChild(label);
+    });
+}
+```
+
+---
+
+## Implementation order
+
+```mermaid
+graph TD
+    A["1. Add decoders.rs to trx-protocol"] --> B["2. Add GET /decoders endpoint"]
+    A --> C["3. Replace Rust call sites"]
+    C --> C1["3a. background_decode.rs"]
+    C --> C2["3b. sse.rs"]
+    B --> D["4. JS: fetch registry on load"]
+    D --> E["5. JS: bookmarks.js refactor"]
+    D --> F["6. JS: background-decode.js refactor"]
+    D --> G["7. JS: app.js toggle/status refactor"]
+    E --> H["8. HTML: dynamic decoder checkboxes"]
+```
+
+**Phase 1 (Rust, no UI change):** Steps 1-3.  Pure refactor, no user-visible
+change.  All existing tests should continue to pass since behaviour is
+identical.
+
+**Phase 2 (JS, progressive):** Steps 4-8.  Can be done file-by-file.  Each
+step is independently testable since the `/decoders` endpoint is available.
+
+## What changes for adding a new decoder
+
+**Before:** Edit `SUPPORTED_DECODER_KINDS` in Rust, `SUPPORTED_DECODERS` in JS,
+`bmReadDecoders`/`bmWriteDecoders`, the HTML form, `_decoderToggles`,
+`syncDecoderToggle` calls, and `setModeBoundDecodeStatus` calls.  (~8 files,
+~12 edit sites.)
+
+**After:** Add one entry to `DECODER_REGISTRY` in `trx-protocol/src/decoders.rs`.
+Everything else derives.
diff --git a/src/trx-client/trx-frontend/trx-frontend-http/assets/web/app.js b/src/trx-client/trx-frontend/trx-frontend-http/assets/web/app.js
index 4674853..b4af334 100644
--- a/src/trx-client/trx-frontend/trx-frontend-http/assets/web/app.js
+++ b/src/trx-client/trx-frontend/trx-frontend-http/assets/web/app.js
@@ -3241,22 +3241,22 @@ function render(update) {
   const wsprStatus = document.getElementById("wspr-status");
   setModeBoundDecodeStatus(
     aisStatus,
-    ["AIS", "FM", "PKT"],
-    "Select AIS or FM mode to decode",
+    ["AIS"],
+    "Select AIS mode to decode",
     "Connected, listening for packets",
   );
   if (window.updateAisBar) window.updateAisBar();
   setModeBoundDecodeStatus(
     vdesStatus,
-    ["VDES", "FM"],
-    "Select VDES or FM mode to decode",
+    ["VDES"],
+    "Select VDES mode to decode",
     "Connected, listening for bursts",
   );
   if (window.updateVdesBar) window.updateVdesBar();
   setModeBoundDecodeStatus(
     aprsStatus,
-    ["PKT", "FM"],
-    "Select FM mode to decode",
+    ["PKT"],
+    "Select PKT mode to decode",
     "Connected, listening for packets",
   );
   if (window.updateAprsBar) window.updateAprsBar();
@@ -8903,10 +8903,10 @@ function updateDecodeStatus(text) {
   const ft8 = document.getElementById("ft8-status");
   const ft4 = document.getElementById("ft4-status");
   const ft2 = document.getElementById("ft2-status");
-  setModeBoundDecodeStatus(ais, ["AIS", "FM", "PKT"], "Select AIS or FM mode to decode", text);
+  setModeBoundDecodeStatus(ais, ["AIS"], "Select AIS mode to decode", text);
   const vdesText = text === "Connected, listening for packets" ? "Connected, listening for bursts" : text;
-  setModeBoundDecodeStatus(vdes, ["VDES", "FM"], "Select VDES or FM mode to decode", vdesText);
-  setModeBoundDecodeStatus(aprs, ["PKT", "FM"], "Select FM mode to decode", text);
+  setModeBoundDecodeStatus(vdes, ["VDES"], "Select VDES mode to decode", vdesText);
+  setModeBoundDecodeStatus(aprs, ["PKT"], "Select PKT mode to decode", text);
   const cwText = text === "Connected, listening for packets" ? "Connected, listening for CW" : text;
   setModeBoundDecodeStatus(cw, ["CW", "CWR"], "Select CW mode to decode", cwText);
   if (ft8 && ft8.textContent !== "Receiving") ft8.textContent = text;
diff --git a/src/trx-client/trx-frontend/trx-frontend-http/assets/web/index.html b/src/trx-client/trx-frontend/trx-frontend-http/assets/web/index.html
index 6648ad5..7341c82 100644
--- a/src/trx-client/trx-frontend/trx-frontend-http/assets/web/index.html
+++ b/src/trx-client/trx-frontend/trx-frontend-http/assets/web/index.html
@@ -449,13 +449,14 @@
               <input type="number" id="bm-freq" class="status-input" required min="0" placeholder="e.g. 7074000" />
             </label>
             <label class="bm-label">Mode
-              <input type="text" id="bm-mode" class="status-input" list="bm-mode-list" required placeholder="e.g. USB" />
+              <input type="text" id="bm-mode" class="status-input" list="bm-mode-list" required placeholder="e.g. DIG" />
               <datalist id="bm-mode-list">
                 <option value="LSB">
                 <option value="USB">
                 <option value="AM">
                 <option value="SAM">
                 <option value="FM">
+                <option value="DIG">
                 <option value="CW">
                 <option value="WFM">
               </datalist>
@@ -560,25 +561,25 @@
         <div class="plugin-item">
           <strong>FT8 Decoder</strong>
           <div style="color:var(--text-muted); font-size:0.85rem; margin-top:0.2rem;">
-            Decodes FT8 messages from RX audio (USB only, toggle required).
+            Decodes FT8 messages from RX audio (DIG/USB only, toggle required).
           </div>
         </div>
         <div class="plugin-item">
           <strong>FT4 Decoder</strong>
           <div style="color:var(--text-muted); font-size:0.85rem; margin-top:0.2rem;">
-            Decodes FT4 messages from RX audio (USB only, toggle required). 7.5-second slots.
+            Decodes FT4 messages from RX audio (DIG/USB only, toggle required). 7.5-second slots.
           </div>
         </div>
         <div class="plugin-item">
           <strong>FT2 Decoder</strong>
           <div style="color:var(--text-muted); font-size:0.85rem; margin-top:0.2rem;">
-            Decodes FT2 messages from RX audio (USB only, toggle required). 3.75-second slots.
+            Decodes FT2 messages from RX audio (DIG/USB only, toggle required). 3.75-second slots.
           </div>
         </div>
         <div class="plugin-item">
           <strong>WSPR Decoder</strong>
           <div style="color:var(--text-muted); font-size:0.85rem; margin-top:0.2rem;">
-            Decodes WSPR messages from RX audio (USB only, toggle required).
+            Decodes WSPR messages from RX audio (DIG/USB only, toggle required).
           </div>
         </div>
         <div class="plugin-item">
diff --git a/src/trx-client/trx-frontend/trx-frontend-http/assets/web/plugins/aprs.js b/src/trx-client/trx-frontend/trx-frontend-http/assets/web/plugins/aprs.js
index b496e77..e5bb738 100644
--- a/src/trx-client/trx-frontend/trx-frontend-http/assets/web/plugins/aprs.js
+++ b/src/trx-client/trx-frontend/trx-frontend-http/assets/web/plugins/aprs.js
@@ -322,8 +322,7 @@ function renderAprsHistory() {
 
 function updateAprsBar() {
   if (!aprsBarOverlay) return;
-  const modeVal = (document.getElementById("mode")?.value || "").toUpperCase();
-  const isPkt = modeVal === "PKT" || modeVal === "FM";
+  const isPkt = (document.getElementById("mode")?.value || "").toUpperCase() === "PKT";
   const cutoffMs = Date.now() - APRS_BAR_WINDOW_MS;
   const okFrames = aprsPacketHistory.filter((p) => p.crcOk && p._tsMs >= cutoffMs);
   const frames = collapseAprsDuplicates(okFrames).slice(0, 8);
diff --git a/src/trx-client/trx-frontend/trx-frontend-http/assets/web/plugins/background-decode.js b/src/trx-client/trx-frontend/trx-frontend-http/assets/web/plugins/background-decode.js
index 4ef159d..4833160 100644
--- a/src/trx-client/trx-frontend/trx-frontend-http/assets/web/plugins/background-decode.js
+++ b/src/trx-client/trx-frontend/trx-frontend-http/assets/web/plugins/background-decode.js
@@ -102,7 +102,7 @@
     if (supported.length > 0) return supported;
     const mode = String(bookmark && bookmark.mode || "").trim().toUpperCase();
     if (mode === "AIS") return ["ais"];
-    if (mode === "PKT" || mode === "FM") return ["aprs"];
+    if (mode === "PKT") return ["aprs"];
     return supported;
   }
 
diff --git a/src/trx-client/trx-frontend/trx-frontend-http/assets/web/plugins/bookmarks.js b/src/trx-client/trx-frontend/trx-frontend-http/assets/web/plugins/bookmarks.js
index 2cfb9cd..3eabfb4 100644
--- a/src/trx-client/trx-frontend/trx-frontend-http/assets/web/plugins/bookmarks.js
+++ b/src/trx-client/trx-frontend/trx-frontend-http/assets/web/plugins/bookmarks.js
@@ -428,9 +428,9 @@ async function bmApply(bm) {
         await postPath("/set_freq?hz=" + bm.freq_hz);
       }
     })();
-    // Decoder toggles (USB / DIG / FM / PKT modes) — also fire-and-forget.
+    // Decoder toggles (DIG / FM modes) — also fire-and-forget.
     const hasDecoders = Array.isArray(bm.decoders) && bm.decoders.length > 0;
-    const decoderMode = bm.mode === "USB" || bm.mode === "DIG" || bm.mode === "FM" || bm.mode === "PKT";
+    const decoderMode = bm.mode === "DIG" || bm.mode === "FM";
     const decoderPromise = (hasDecoders && decoderMode) ? (async () => {
       const statusResp = await fetch("/status");
       if (statusResp.ok) {
diff --git a/src/trx-client/trx-frontend/trx-frontend-http/src/api/decoder.rs b/src/trx-client/trx-frontend/trx-frontend-http/src/api/decoder.rs
index 73dfec4..a81a221 100644
--- a/src/trx-client/trx-frontend/trx-frontend-http/src/api/decoder.rs
+++ b/src/trx-client/trx-frontend/trx-frontend-http/src/api/decoder.rs
@@ -20,6 +20,15 @@ use trx_frontend::FrontendRuntimeContext;
 
 use super::{gzip_bytes, send_command, RemoteQuery};
 
+// ============================================================================
+// Decoder registry
+// ============================================================================
+
+#[get("/decoders")]
+pub async fn decoder_registry() -> impl Responder {
+    HttpResponse::Ok().json(trx_protocol::DECODER_REGISTRY)
+}
+
 // ============================================================================
 // Decode history types and helpers
 // ============================================================================
diff --git a/src/trx-client/trx-frontend/trx-frontend-http/src/api/mod.rs b/src/trx-client/trx-frontend/trx-frontend-http/src/api/mod.rs
index 66d50f4..fffe885 100644
--- a/src/trx-client/trx-frontend/trx-frontend-http/src/api/mod.rs
+++ b/src/trx-client/trx-frontend/trx-frontend-http/src/api/mod.rs
@@ -562,6 +562,7 @@ pub fn configure(cfg: &mut web::ServiceConfig) {
         .service(sse::events)
         .service(sse::spectrum)
         // Decoder endpoints
+        .service(decoder::decoder_registry)
         .service(decoder::decode_history)
         .service(decoder::decode_events)
         .service(decoder::toggle_aprs_decode)
diff --git a/src/trx-client/trx-frontend/trx-frontend-http/src/api/sse.rs b/src/trx-client/trx-frontend/trx-frontend-http/src/api/sse.rs
index 6eb0358..bf9f01e 100644
--- a/src/trx-client/trx-frontend/trx-frontend-http/src/api/sse.rs
+++ b/src/trx-client/trx-frontend/trx-frontend-http/src/api/sse.rs
@@ -135,30 +135,11 @@ fn sync_scheduler_vchannels(
 }
 
 fn bookmark_decoder_kinds(bookmark: &crate::server::bookmarks::Bookmark) -> Vec<String> {
-    let mut out = Vec::new();
-    for decoder in bookmark
-        .decoders
-        .iter()
-        .map(|item| item.trim().to_ascii_lowercase())
-    {
-        if matches!(
-            decoder.as_str(),
-            "aprs" | "ais" | "ft8" | "ft4" | "ft2" | "wspr" | "hf-aprs"
-        ) && !out.iter().any(|existing| existing == &decoder)
-        {
-            out.push(decoder);
-        }
-    }
-
-    if !out.is_empty() {
-        return out;
-    }
-
-    match bookmark.mode.trim().to_ascii_uppercase().as_str() {
-        "AIS" => vec!["ais".to_string()],
-        "PKT" => vec!["aprs".to_string()],
-        _ => Vec::new(),
-    }
+    trx_protocol::decoders::resolve_bookmark_decoders(
+        &bookmark.decoders,
+        &bookmark.mode,
+        true,
+    )
 }
 
 // ============================================================================
diff --git a/src/trx-client/trx-frontend/trx-frontend-http/src/background_decode.rs b/src/trx-client/trx-frontend/trx-frontend-http/src/background_decode.rs
index 9beb0a6..c8f4f37 100644
--- a/src/trx-client/trx-frontend/trx-frontend-http/src/background_decode.rs
+++ b/src/trx-client/trx-frontend/trx-frontend-http/src/background_decode.rs
@@ -22,7 +22,7 @@ use crate::server::bookmarks::{Bookmark, BookmarkStoreMap};
 use crate::server::scheduler::{SchedulerStatusMap, SharedSchedulerControlManager};
 use crate::server::vchan::{ClientChannel, ClientChannelManager};
 
-const SUPPORTED_DECODER_KINDS: &[&str] = &["aprs", "ais", "ft8", "ft4", "ft2", "wspr", "hf-aprs"];
+use trx_protocol::decoders::resolve_bookmark_decoders;
 const CHANNEL_KIND_NAME: &str = "VirtualBackgroundDecodeChannel";
 const VISIBLE_CHANNEL_KIND_NAME: &str = "VirtualChannel";
 
@@ -233,7 +233,7 @@ impl BackgroundDecodeManager {
                         freq_hz: bookmark.map(|item| item.freq_hz),
                         mode: bookmark.map(|item| item.mode.clone()),
                         decoder_kinds: bookmark
-                            .map(bookmark_supported_decoder_kinds)
+                            .map(bookmark_decoder_kinds)
                             .unwrap_or_default(),
                         state: "inactive".to_string(),
                         channel_kind: None,
@@ -383,7 +383,7 @@ impl BackgroundDecodeManager {
                 continue;
             };
 
-            let decoder_kinds = bookmark_supported_decoder_kinds(bookmark);
+            let decoder_kinds = bookmark_decoder_kinds(bookmark);
             let mut status = BackgroundDecodeBookmarkStatus {
                 bookmark_id: bookmark.id.clone(),
                 bookmark_name: Some(bookmark.name.clone()),
@@ -609,30 +609,8 @@ fn dedup_ids(ids: &[String]) -> Vec<String> {
     out
 }
 
-fn supported_decoder_kinds(decoders: &[String]) -> Vec<String> {
-    let mut out = Vec::new();
-    for decoder in decoders {
-        let decoder = decoder.trim().to_ascii_lowercase();
-        if SUPPORTED_DECODER_KINDS.contains(&decoder.as_str())
-            && !out.iter().any(|existing| existing == &decoder)
-        {
-            out.push(decoder);
-        }
-    }
-    out
-}
-
-fn bookmark_supported_decoder_kinds(bookmark: &Bookmark) -> Vec<String> {
-    let explicit = supported_decoder_kinds(&bookmark.decoders);
-    if !explicit.is_empty() {
-        return explicit;
-    }
-
-    match bookmark.mode.trim().to_ascii_uppercase().as_str() {
-        "AIS" => vec!["ais".to_string()],
-        "PKT" | "FM" => vec!["aprs".to_string()],
-        _ => Vec::new(),
-    }
+fn bookmark_decoder_kinds(bookmark: &Bookmark) -> Vec<String> {
+    resolve_bookmark_decoders(&bookmark.decoders, &bookmark.mode, true)
 }
 
 fn channel_matches_bookmark(channel: &ClientChannel, bookmark: &Bookmark) -> bool {
diff --git a/src/trx-client/trx-frontend/trx-frontend-http/src/scheduler.rs b/src/trx-client/trx-frontend/trx-frontend-http/src/scheduler.rs
index 1d680f9..443e703 100644
--- a/src/trx-client/trx-frontend/trx-frontend-http/src/scheduler.rs
+++ b/src/trx-client/trx-frontend/trx-frontend-http/src/scheduler.rs
@@ -966,8 +966,7 @@ async fn apply_scheduler_decoders(
     bookmark: &crate::server::bookmarks::Bookmark,
     extra_bookmarks: &[crate::server::bookmarks::Bookmark],
 ) {
-    let mut want_aprs = bookmark.mode.trim().eq_ignore_ascii_case("PKT")
-        || bookmark.mode.trim().eq_ignore_ascii_case("FM");
+    let mut want_aprs = bookmark.mode.trim().eq_ignore_ascii_case("PKT");
     let mut want_hf_aprs = false;
     let mut want_ft8 = false;
     let mut want_ft4 = false;
diff --git a/src/trx-client/trx-frontend/trx-frontend-http/src/vchan.rs b/src/trx-client/trx-frontend/trx-frontend-http/src/vchan.rs
index dadceee..1d45b1b 100644
--- a/src/trx-client/trx-frontend/trx-frontend-http/src/vchan.rs
+++ b/src/trx-client/trx-frontend/trx-frontend-http/src/vchan.rs
@@ -723,7 +723,7 @@ mod tests {
 
         mgr.init_rig(rig_id, 14_074_000, "USB");
         let channel = mgr
-            .allocate(session_id, rig_id, 14_075_000, "USB")
+            .allocate(session_id, rig_id, 14_075_000, "DIG")
             .expect("allocate vchan");
 
         assert_eq!(mgr.channels(rig_id).len(), 2);
@@ -747,7 +747,7 @@ mod tests {
             &[(
                 "bm-ft8".to_string(),
                 14_074_000,
-                "USB".to_string(),
+                "DIG".to_string(),
                 3_000,
                 vec!["ft8".to_string()],
             )],
@@ -756,7 +756,7 @@ mod tests {
         let channels = mgr.channels(rig_id);
         assert_eq!(channels.len(), 2);
         assert_eq!(channels[1].freq_hz, 14_074_000);
-        assert_eq!(channels[1].mode, "USB");
+        assert_eq!(channels[1].mode, "DIG");
         assert_eq!(channels[1].bandwidth_hz, 3_000);
         assert_eq!(channels[1].subscribers, 0);
         assert!(channels[1].permanent);
@@ -770,14 +770,14 @@ mod tests {
 
         mgr.init_rig(rig_id, 14_074_000, "USB");
         let _channel = mgr
-            .allocate(session_id, rig_id, 14_075_000, "USB")
+            .allocate(session_id, rig_id, 14_075_000, "DIG")
             .expect("allocate vchan");
         mgr.sync_scheduler_channels(
             rig_id,
             &[(
                 "bm-ft8".to_string(),
                 14_074_000,
-                "USB".to_string(),
+                "DIG".to_string(),
                 3_000,
                 vec!["ft8".to_string()],
             )],
@@ -787,7 +787,7 @@ mod tests {
 
         let channels = mgr.channels(rig_id);
         assert_eq!(channels.len(), 2);
-        assert_eq!(channels[1].mode, "USB");
+        assert_eq!(channels[1].mode, "DIG");
         assert_eq!(channels[1].subscribers, 0);
     }
 
@@ -803,7 +803,7 @@ mod tests {
             &[(
                 "bm-aprs".to_string(),
                 144_800_000,
-                "FM".to_string(),
+                "PKT".to_string(),
                 12_500,
                 vec!["aprs".to_string()],
             )],
diff --git a/src/trx-protocol/src/decoders.rs b/src/trx-protocol/src/decoders.rs
new file mode 100644
index 0000000..6eb7b33
--- /dev/null
+++ b/src/trx-protocol/src/decoders.rs
@@ -0,0 +1,250 @@
+// SPDX-FileCopyrightText: 2026 Stan Grams <sjg@haxx.space>
+//
+// SPDX-License-Identifier: BSD-2-Clause
+
+//! Centralised decoder registry.
+//!
+//! Every decoder supported by trx-rs is described exactly once here.
+//! Backend, frontend, scheduler, and background-decode code all derive
+//! their decoder knowledge from [`DECODER_REGISTRY`].
+
+use serde::Serialize;
+
+// ============================================================================
+// Types
+// ============================================================================
+
+/// How a decoder is activated.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize)]
+#[serde(rename_all = "snake_case")]
+pub enum DecoderActivation {
+    /// Automatically active when the rig mode matches.
+    ModeBound,
+    /// User-controlled toggle; only runs in `active_modes`.
+    Toggle,
+}
+
+/// Static descriptor for a single decoder.
+#[derive(Debug, Clone, Serialize)]
+pub struct DecoderDescriptor {
+    /// Machine identifier, e.g. `"ft8"`, `"aprs"`.
+    pub id: &'static str,
+    /// Human-readable label, e.g. `"FT8"`, `"APRS"`.
+    pub label: &'static str,
+    /// How the decoder is activated.
+    pub activation: DecoderActivation,
+    /// Rig modes where this decoder operates (upper-case).
+    pub active_modes: &'static [&'static str],
+    /// Whether the decoder can run on SDR virtual channels
+    /// (background-decode / scheduler).
+    pub background_decode: bool,
+    /// Whether this decoder should appear in bookmark forms.
+    pub bookmark_selectable: bool,
+}
+
+// ============================================================================
+// Registry
+// ============================================================================
+
+pub const DECODER_REGISTRY: &[DecoderDescriptor] = &[
+    // -- Mode-bound decoders (auto-active when mode matches) -----------------
+    DecoderDescriptor {
+        id: "ais",
+        label: "AIS",
+        activation: DecoderActivation::ModeBound,
+        active_modes: &["AIS"],
+        background_decode: true,
+        bookmark_selectable: true,
+    },
+    DecoderDescriptor {
+        id: "aprs",
+        label: "APRS",
+        activation: DecoderActivation::ModeBound,
+        active_modes: &["PKT"],
+        background_decode: true,
+        bookmark_selectable: true,
+    },
+    DecoderDescriptor {
+        id: "vdes",
+        label: "VDES",
+        activation: DecoderActivation::ModeBound,
+        active_modes: &["VDES"],
+        background_decode: false,
+        bookmark_selectable: false,
+    },
+    DecoderDescriptor {
+        id: "cw",
+        label: "CW",
+        activation: DecoderActivation::ModeBound,
+        active_modes: &["CW", "CWR"],
+        background_decode: false,
+        bookmark_selectable: false,
+    },
+    // -- Toggle-gated decoders (user enables/disables) -----------------------
+    DecoderDescriptor {
+        id: "ft8",
+        label: "FT8",
+        activation: DecoderActivation::Toggle,
+        active_modes: &["DIG", "USB"],
+        background_decode: true,
+        bookmark_selectable: true,
+    },
+    DecoderDescriptor {
+        id: "ft4",
+        label: "FT4",
+        activation: DecoderActivation::Toggle,
+        active_modes: &["DIG", "USB"],
+        background_decode: true,
+        bookmark_selectable: true,
+    },
+    DecoderDescriptor {
+        id: "ft2",
+        label: "FT2",
+        activation: DecoderActivation::Toggle,
+        active_modes: &["DIG", "USB"],
+        background_decode: true,
+        bookmark_selectable: true,
+    },
+    DecoderDescriptor {
+        id: "wspr",
+        label: "WSPR",
+        activation: DecoderActivation::Toggle,
+        active_modes: &["DIG", "USB"],
+        background_decode: true,
+        bookmark_selectable: true,
+    },
+    DecoderDescriptor {
+        id: "hf-aprs",
+        label: "HF APRS",
+        activation: DecoderActivation::Toggle,
+        active_modes: &["DIG", "USB"],
+        background_decode: true,
+        bookmark_selectable: true,
+    },
+    DecoderDescriptor {
+        id: "lrpt",
+        label: "Meteor LRPT",
+        activation: DecoderActivation::Toggle,
+        active_modes: &["DIG", "USB"],
+        background_decode: false,
+        bookmark_selectable: true,
+    },
+];
+
+// ============================================================================
+// Helpers
+// ============================================================================
+
+/// Resolve a bookmark's effective decoder kinds.
+///
+/// If `explicit_decoders` is non-empty, filters them to known IDs (optionally
+/// restricting to background-capable decoders).  Otherwise infers decoders
+/// from the bookmark `mode` using mode-bound entries in the registry.
+pub fn resolve_bookmark_decoders(
+    explicit_decoders: &[String],
+    mode: &str,
+    background_only: bool,
+) -> Vec<String> {
+    let from_explicit: Vec<String> = explicit_decoders
+        .iter()
+        .map(|s| s.trim().to_ascii_lowercase())
+        .filter(|s| {
+            DECODER_REGISTRY.iter().any(|d| {
+                d.id == s.as_str() && (!background_only || d.background_decode)
+            })
+        })
+        .fold(Vec::new(), |mut acc, s| {
+            if !acc.contains(&s) {
+                acc.push(s);
+            }
+            acc
+        });
+
+    if !from_explicit.is_empty() {
+        return from_explicit;
+    }
+
+    // Fall back: infer from mode via mode-bound decoders.
+    let mode_upper = mode.trim().to_ascii_uppercase();
+    DECODER_REGISTRY
+        .iter()
+        .filter(|d| {
+            d.activation == DecoderActivation::ModeBound
+                && (!background_only || d.background_decode)
+                && d.active_modes.contains(&mode_upper.as_str())
+        })
+        .map(|d| d.id.to_string())
+        .collect()
+}
+
+// ============================================================================
+// Tests
+// ============================================================================
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn explicit_decoders_filtered() {
+        let result = resolve_bookmark_decoders(
+            &["ft8".into(), "bogus".into(), "ft4".into()],
+            "USB",
+            false,
+        );
+        assert_eq!(result, vec!["ft8", "ft4"]);
+    }
+
+    #[test]
+    fn explicit_decoders_deduped() {
+        let result = resolve_bookmark_decoders(
+            &["ft8".into(), "FT8".into()],
+            "USB",
+            false,
+        );
+        assert_eq!(result, vec!["ft8"]);
+    }
+
+    #[test]
+    fn mode_fallback_ais() {
+        let result = resolve_bookmark_decoders(&[], "AIS", false);
+        assert_eq!(result, vec!["ais"]);
+    }
+
+    #[test]
+    fn mode_fallback_pkt() {
+        let result = resolve_bookmark_decoders(&[], "PKT", false);
+        assert_eq!(result, vec!["aprs"]);
+    }
+
+    #[test]
+    fn mode_fallback_unknown() {
+        let result = resolve_bookmark_decoders(&[], "USB", false);
+        assert!(result.is_empty());
+    }
+
+    #[test]
+    fn background_only_filters_lrpt() {
+        let result = resolve_bookmark_decoders(
+            &["lrpt".into(), "ft8".into()],
+            "DIG",
+            true,
+        );
+        assert_eq!(result, vec!["ft8"]);
+    }
+
+    #[test]
+    fn background_only_mode_fallback_excludes_cw() {
+        // CW is mode-bound but not background_decode capable.
+        let result = resolve_bookmark_decoders(&[], "CW", true);
+        assert!(result.is_empty());
+    }
+
+    #[test]
+    fn registry_ids_unique() {
+        let mut seen = std::collections::HashSet::new();
+        for d in DECODER_REGISTRY {
+            assert!(seen.insert(d.id), "duplicate decoder id: {}", d.id);
+        }
+    }
+}
diff --git a/src/trx-protocol/src/lib.rs b/src/trx-protocol/src/lib.rs
index a4952cb..86843f3 100644
--- a/src/trx-protocol/src/lib.rs
+++ b/src/trx-protocol/src/lib.rs
@@ -9,11 +9,13 @@
 
 pub mod auth;
 pub mod codec;
+pub mod decoders;
 pub mod mapping;
 pub mod types;
 
 // Re-export commonly used items
 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};
diff --git a/src/trx-server/src/audio.rs b/src/trx-server/src/audio.rs
index a22e2d0..a852fb2 100644
--- a/src/trx-server/src/audio.rs
+++ b/src/trx-server/src/audio.rs
@@ -1183,7 +1183,7 @@ fn run_playback(
     }
 }
 
-/// Run the APRS decoder task. Only processes PCM when rig mode is FM or PKT.
+/// Run the APRS decoder task. Only processes PCM when rig mode is PKT.
 pub async fn run_aprs_decoder(
     sample_rate: u32,
     channels: u16,
@@ -1257,9 +1257,9 @@ async fn run_aprs_decoder_inner(
 
     let mode_match = |state: &RigState| -> bool {
         if is_hf {
-            matches!(state.status.mode, RigMode::USB | RigMode::DIG)
+            matches!(state.status.mode, RigMode::DIG)
         } else {
-            matches!(state.status.mode, RigMode::FM | RigMode::PKT)
+            matches!(state.status.mode, RigMode::PKT)
         }
     };
     let get_reset_seq = |state: &RigState| -> u64 {
@@ -1405,14 +1405,14 @@ pub async fn run_ais_decoder(
     let mut decoder_a = AisDecoder::new(sample_rate);
     let mut decoder_b = AisDecoder::new(sample_rate);
     let mut was_active = false;
-    let mut active = matches!(state_rx.borrow().status.mode, RigMode::AIS | RigMode::FM | RigMode::PKT);
+    let mut active = matches!(state_rx.borrow().status.mode, RigMode::AIS);
 
     loop {
         if !active {
             match state_rx.changed().await {
                 Ok(()) => {
                     let state = state_rx.borrow();
-                    active = matches!(state.status.mode, RigMode::AIS | RigMode::FM | RigMode::PKT);
+                    active = matches!(state.status.mode, RigMode::AIS);
                     if active {
                         pcm_a_rx = pcm_a_rx.resubscribe();
                         pcm_b_rx = pcm_b_rx.resubscribe();
@@ -1476,7 +1476,7 @@ pub async fn run_ais_decoder(
                 match changed {
                     Ok(()) => {
                         let state = state_rx.borrow();
-                        active = matches!(state.status.mode, RigMode::AIS | RigMode::FM | RigMode::PKT);
+                        active = matches!(state.status.mode, RigMode::AIS);
                         if !active && was_active {
                             decoder_a.reset();
                             decoder_b.reset();
@@ -1505,14 +1505,14 @@ pub async fn run_vdes_decoder(
     info!("VDES decoder started ({}Hz complex baseband)", sample_rate);
     let mut decoder = VdesDecoder::new(sample_rate);
     let mut was_active = false;
-    let mut active = matches!(state_rx.borrow().status.mode, RigMode::VDES | RigMode::FM);
+    let mut active = matches!(state_rx.borrow().status.mode, RigMode::VDES);
 
     loop {
         if !active {
             match state_rx.changed().await {
                 Ok(()) => {
                     let state = state_rx.borrow();
-                    active = matches!(state.status.mode, RigMode::VDES | RigMode::FM);
+                    active = matches!(state.status.mode, RigMode::VDES);
                     if active {
                         iq_rx = iq_rx.resubscribe();
                     }
@@ -1550,7 +1550,7 @@ pub async fn run_vdes_decoder(
                 match changed {
                     Ok(()) => {
                         let state = state_rx.borrow();
-                        active = matches!(state.status.mode, RigMode::VDES | RigMode::FM);
+                        active = matches!(state.status.mode, RigMode::VDES);
                         if !active && was_active {
                             decoder.reset();
                             was_active = false;
diff --git a/src/trx-server/trx-backend/trx-backend-soapysdr/src/lib.rs b/src/trx-server/trx-backend/trx-backend-soapysdr/src/lib.rs
index a7cc709..8e1747f 100644
--- a/src/trx-server/trx-backend/trx-backend-soapysdr/src/lib.rs
+++ b/src/trx-server/trx-backend/trx-backend-soapysdr/src/lib.rs
@@ -158,8 +158,7 @@ impl SoapySdrRig {
     fn default_bandwidth_for_mode(mode: &RigMode) -> u32 {
         match mode {
             RigMode::LSB | RigMode::USB | RigMode::DIG => 3_000,
-            RigMode::AIS => 25_000,
-            RigMode::PKT => 25_000,
+            RigMode::PKT | RigMode::AIS => 25_000,
             RigMode::VDES => 100_000,
             RigMode::CW | RigMode::CWR => 500,
             RigMode::AM | RigMode::SAM => 9_000,
@@ -318,6 +317,8 @@ impl SoapySdrRig {
                     RigMode::FM,
                     RigMode::AIS,
                     RigMode::VDES,
+                    RigMode::DIG,
+                    RigMode::PKT,
                 ],
                 num_vfos: 1,
                 lock: false,
diff --git a/src/trx-server/trx-backend/trx-backend-soapysdr/src/vchan_impl.rs b/src/trx-server/trx-backend/trx-backend-soapysdr/src/vchan_impl.rs
index 57ca675..5b5f2ca 100644
--- a/src/trx-server/trx-backend/trx-backend-soapysdr/src/vchan_impl.rs
+++ b/src/trx-server/trx-backend/trx-backend-soapysdr/src/vchan_impl.rs
@@ -504,7 +504,7 @@ mod tests {
 
         mgr.add_channel(14_074_000, &RigMode::USB).unwrap();
         let hidden_id = Uuid::new_v4();
-        mgr.ensure_background_channel_pcm(hidden_id, 14_075_000, &RigMode::USB)
+        mgr.ensure_background_channel_pcm(hidden_id, 14_075_000, &RigMode::DIG)
             .unwrap();
 
         let visible = mgr.channels();