diff --git a/crates/openlogi-agent/src/bin/mock_agent.rs b/crates/openlogi-agent/src/bin/mock_agent.rs
index 679589096..81c4dbb72 100644
--- a/crates/openlogi-agent/src/bin/mock_agent.rs
+++ b/crates/openlogi-agent/src/bin/mock_agent.rs
@@ -429,10 +429,7 @@ fn standalone_light() -> StandaloneDevice {
             zones: false,
         }),
         driver_id: "litra".to_string(),
-        // Must stay `Some` until #571 is fixed: `registry_model_id` is
-        // `skip_serializing_if`, which truncates the bincode stream when it is
-        // `None` and makes the whole snapshot undecodable. `8c900` is also the
-        // real registry id for a Litra Glow, so the asset lookup resolves.
+        // `8c900` is the real registry id for a Litra Glow, so the asset lookup resolves.
         registry_model_id: Some("8c900".to_string()),
     }
 }
diff --git a/crates/openlogi-core/src/device.rs b/crates/openlogi-core/src/device.rs
index d12f592ad..68ef6de13 100644
--- a/crates/openlogi-core/src/device.rs
+++ b/crates/openlogi-core/src/device.rs
@@ -407,7 +407,7 @@ pub struct StandaloneDevice {
     ///
     /// This is deliberately appended: `StandaloneDevice` crosses the
     /// append-only GUI↔agent bincode wire format.
-    #[serde(default, skip_serializing_if = "Option::is_none")]
+    #[serde(default)]
     pub registry_model_id: Option<String>,
 }
 
diff --git a/crates/openlogi-ipc/src/ipc.rs b/crates/openlogi-ipc/src/ipc.rs
index 391daf121..fdc218dbb 100644
--- a/crates/openlogi-ipc/src/ipc.rs
+++ b/crates/openlogi-ipc/src/ipc.rs
@@ -52,7 +52,8 @@ pub use succession::Identity;
 ///      [`RingObservation`]).
 /// v22: DPI scalar values use the validated [`Dpi`] type end to end.
 /// v23: SmartShift writes carry one typed [`SmartShiftStatus`] value.
-pub const PROTOCOL_VERSION: u32 = 23;
+/// v24: `StandaloneDevice::registry_model_id` is always encoded (bincode fix).
+pub const PROTOCOL_VERSION: u32 = 24;
 
 /// Environment variable through which the agent hands a supervised helper the
 /// run token it will serve, so the helper knows which agent it belongs to
diff --git a/crates/openlogi-ipc/tests/wire_format.rs b/crates/openlogi-ipc/tests/wire_format.rs
index 5c293843c..2b3eb2447 100644
--- a/crates/openlogi-ipc/tests/wire_format.rs
+++ b/crates/openlogi-ipc/tests/wire_format.rs
@@ -63,12 +63,31 @@ fn wire_bytes<T: serde::Serialize>(value: &T) -> String {
 }
 
 #[track_caller]
-fn assert_wire<T: serde::Serialize>(value: &T, golden: &str) {
+fn assert_wire<T>(value: &T, golden: &str)
+where
+    T: serde::Serialize + serde::de::DeserializeOwned + std::fmt::Debug,
+{
+    let hex = wire_bytes(value);
     assert_eq!(
-        wire_bytes(value),
-        golden,
+        hex, golden,
         "wire encoding changed — if intentional, bump PROTOCOL_VERSION and regenerate this golden"
     );
+    let bytes = (0..hex.len())
+        .step_by(2)
+        .map(|i| u8::from_str_radix(&hex[i..i + 2], 16).expect("valid hex"))
+        .collect::<Vec<u8>>();
+    let decoded: T = bincode::DefaultOptions::new()
+        .deserialize(&bytes)
+        .expect("wire types deserialize");
+    // Re-encode the decoded value and compare — this validates the round-trip
+    // without requiring `PartialEq` on every wire type (e.g. `AgentRequest`
+    // generated by tarpc, `WriteError`). For types that do implement
+    // `PartialEq`, this is equivalent to `decoded == value`.
+    let re_hex = wire_bytes(&decoded);
+    assert_eq!(
+        hex, re_hex,
+        "wire round-trip failed — re-encoded bytes differ"
+    );
 }
 
 fn representative_smartshift_status() -> SmartShiftStatus {
@@ -85,7 +104,7 @@ fn representative_smartshift_status() -> SmartShiftStatus {
 /// that makes that visible in the same diff.
 #[test]
 fn protocol_version_is_pinned() {
-    assert_eq!(PROTOCOL_VERSION, 23);
+    assert_eq!(PROTOCOL_VERSION, 24);
 }
 
 #[test]
@@ -511,7 +530,7 @@ fn standalone_light_dtos_commands_and_errors() {
     legacy.registry_model_id = None;
     assert_wire(
         &legacy,
-        "fb6d04fb00c9fb43fffb02020d73657269616c3a676c6f772d310a4c6974726120476c6f7701044c6f67690106676c6f772d31000000000d010001010114fa010101fb8c0afb641964020000056c69747261",
+        "fb6d04fb00c9fb43fffb02020d73657269616c3a676c6f772d310a4c6974726120476c6f7701044c6f67690106676c6f772d31000000000d010001010114fa010101fb8c0afb641964020000056c6974726100",
     );
     assert_wire(&capabilities, "010114fa010101fb8c0afb641964020000");
     assert_wire(&brightness, "14fa0101");