diff --git a/v2/crates/wifi-densepose-hardware/src/lib.rs b/v2/crates/wifi-densepose-hardware/src/lib.rs
index 23838ad9..edf61cb4 100644
--- a/v2/crates/wifi-densepose-hardware/src/lib.rs
+++ b/v2/crates/wifi-densepose-hardware/src/lib.rs
@@ -37,6 +37,7 @@
 mod csi_frame;
 mod error;
 mod esp32_parser;
+pub mod sync_packet;
 pub mod aggregator;
 mod bridge;
 pub mod esp32;
@@ -55,6 +56,9 @@ pub use esp32_parser::{
     RUVIEW_FEATURE_STATE_MAGIC, RUVIEW_TEMPORAL_MAGIC,
 };
 pub use bridge::CsiData;
+pub use sync_packet::{
+    SyncPacket, SyncPacketFlags, SYNC_PACKET_MAGIC, SYNC_PACKET_SIZE, SYNC_PACKET_PROTO_VER,
+};
 pub use radio_ops::{
     RadioOps, RadioMode, CaptureProfile, RadioHealth, RadioError, MockRadio,
     MeshRole, MeshMsgType, AuthClass, MeshHeader, NodeStatus, AnomalyAlert,
diff --git a/v2/crates/wifi-densepose-hardware/src/sync_packet.rs b/v2/crates/wifi-densepose-hardware/src/sync_packet.rs
new file mode 100644
index 00000000..60f6f5dc
--- /dev/null
+++ b/v2/crates/wifi-densepose-hardware/src/sync_packet.rs
@@ -0,0 +1,246 @@
+//! ADR-110 §A0.12 sync packet decoder (firmware v0.6.9+).
+//!
+//! Emitted by the firmware on the same UDP socket as ADR-018 CSI frames,
+//! distinguished by leading magic `0xC511A110`. Pairs `(node_id, sequence)`
+//! across the two UDP streams so a host aggregator can recover mesh-aligned
+//! timestamps for every CSI frame — see `WITNESS-LOG-110 §A0.12` for live
+//! verification, `archive/v1/src/hardware/csi_extractor.py:SyncPacketParser`
+//! for the matching Python decoder.
+//!
+//! Wire format (32 bytes, little-endian):
+//! ```text
+//! [0..3]   magic 0xC511A110 (LE u32)
+//! [4]      node_id
+//! [5]      proto_ver (currently 0x01)
+//! [6]      flags: bit 0 = is_leader
+//!                 bit 1 = is_valid (fresh sync within VALID_WINDOW_MS)
+//!                 bit 2 = smoothed_used (EMA filter active)
+//! [7]      reserved
+//! [8..15]  local esp_timer_get_time() (u64)
+//! [16..23] mesh-aligned epoch = local + smoothed offset (u64)
+//! [24..27] high-water CSI sequence (u32) — pairing key against ADR-018 frames
+//! [28..31] reserved
+//! ```
+//!
+//! Recover the per-board offset for a given sync packet as
+//! `local_us - epoch_us` (signed). Follower nodes report the EMA-smoothed
+//! offset measured in §A0.10; leader nodes report `~0` modulo call-stack
+//! elapsed time (`leader_epoch_us = now_us` by definition).
+
+use serde::{Deserialize, Serialize};
+
+use crate::error::ParseError;
+
+/// Magic constant in the first 4 little-endian bytes of every sync packet.
+pub const SYNC_PACKET_MAGIC: u32 = 0xC511_A110;
+/// Total wire size of a v0.6.9+ sync packet.
+pub const SYNC_PACKET_SIZE: usize = 32;
+/// Wire protocol version currently emitted by firmware.
+pub const SYNC_PACKET_PROTO_VER: u8 = 0x01;
+
+/// Decoded ADR-110 §A0.12 sync packet.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+pub struct SyncPacket {
+    pub node_id: u8,
+    pub proto_ver: u8,
+    pub flags: SyncPacketFlags,
+    /// Node-local `esp_timer_get_time()` snapshot at emission time.
+    pub local_us: u64,
+    /// Mesh-aligned epoch — `local_us + smoothed_offset`.
+    pub epoch_us: u64,
+    /// High-water ADR-018 CSI sequence number at emission time. Host
+    /// aggregator pairs (`node_id`, `sequence`) across the two UDP streams
+    /// to apply the recovered offset back to in-flight CSI frames.
+    pub sequence: u32,
+}
+
+/// Flag bits packed into byte 6 of the sync packet.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize, Default)]
+pub struct SyncPacketFlags {
+    pub is_leader: bool,
+    pub is_valid: bool,
+    pub smoothed_used: bool,
+}
+
+impl SyncPacketFlags {
+    pub fn from_byte(b: u8) -> Self {
+        Self {
+            is_leader: (b & 0x01) != 0,
+            is_valid: (b & 0x02) != 0,
+            smoothed_used: (b & 0x04) != 0,
+        }
+    }
+
+    pub fn to_byte(self) -> u8 {
+        let mut b = 0u8;
+        if self.is_leader { b |= 0x01; }
+        if self.is_valid { b |= 0x02; }
+        if self.smoothed_used { b |= 0x04; }
+        b
+    }
+}
+
+impl SyncPacket {
+    /// Decode a 32-byte sync packet. Returns `ParseError::InvalidMagic` if
+    /// the leading u32 doesn't match `SYNC_PACKET_MAGIC` (host should
+    /// dispatch on the magic before calling this — see crate-level docs).
+    pub fn from_bytes(buf: &[u8]) -> Result<Self, ParseError> {
+        if buf.len() < SYNC_PACKET_SIZE {
+            return Err(ParseError::InsufficientData {
+                needed: SYNC_PACKET_SIZE,
+                got: buf.len(),
+            });
+        }
+        let magic = u32::from_le_bytes(buf[0..4].try_into().unwrap());
+        if magic != SYNC_PACKET_MAGIC {
+            return Err(ParseError::InvalidMagic { expected: SYNC_PACKET_MAGIC, got: magic });
+        }
+        let node_id = buf[4];
+        let proto_ver = buf[5];
+        let flags = SyncPacketFlags::from_byte(buf[6]);
+        // buf[7] reserved
+        let local_us = u64::from_le_bytes(buf[8..16].try_into().unwrap());
+        let epoch_us = u64::from_le_bytes(buf[16..24].try_into().unwrap());
+        let sequence = u32::from_le_bytes(buf[24..28].try_into().unwrap());
+        // buf[28..32] reserved
+        Ok(Self {
+            node_id,
+            proto_ver,
+            flags,
+            local_us,
+            epoch_us,
+            sequence,
+        })
+    }
+
+    /// Recover the signed offset between this node's local monotonic clock
+    /// and the mesh epoch (`local_us - epoch_us`). For followers this is
+    /// the EMA-smoothed offset; for leaders this is approximately 0 (a few
+    /// µs of call-stack elapsed only).
+    pub fn local_minus_epoch_us(&self) -> i64 {
+        (self.local_us as i64) - (self.epoch_us as i64)
+    }
+
+    /// Serialize back to wire bytes (32 bytes, little-endian).
+    pub fn to_bytes(&self) -> [u8; SYNC_PACKET_SIZE] {
+        let mut out = [0u8; SYNC_PACKET_SIZE];
+        out[0..4].copy_from_slice(&SYNC_PACKET_MAGIC.to_le_bytes());
+        out[4] = self.node_id;
+        out[5] = self.proto_ver;
+        out[6] = self.flags.to_byte();
+        // out[7] reserved zero
+        out[8..16].copy_from_slice(&self.local_us.to_le_bytes());
+        out[16..24].copy_from_slice(&self.epoch_us.to_le_bytes());
+        out[24..28].copy_from_slice(&self.sequence.to_le_bytes());
+        // out[28..32] reserved zero
+        out
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// Reproduces the COM9 follower sync-pkt #1 captured in WITNESS-LOG-110 §A0.12.
+    #[test]
+    fn follower_typical_packet_roundtrips() {
+        let pkt = SyncPacket {
+            node_id: 9,
+            proto_ver: 1,
+            flags: SyncPacketFlags { is_leader: false, is_valid: true, smoothed_used: true },
+            local_us: 28_798_450,
+            epoch_us: 27_634_885,
+            sequence: 20,
+        };
+        let wire = pkt.to_bytes();
+        let decoded = SyncPacket::from_bytes(&wire).unwrap();
+        assert_eq!(decoded, pkt);
+        // The 1.16-second boot delta §A0.10 measured between COM9 and COM12.
+        assert_eq!(decoded.local_minus_epoch_us(), 1_163_565);
+        assert_eq!(decoded.flags.to_byte(), 0x06);
+    }
+
+    /// COM12 leader case from WITNESS-LOG-110 §A0.12: flags=0x03, epoch ≈ local.
+    #[test]
+    fn leader_packet_has_local_close_to_epoch() {
+        let pkt = SyncPacket {
+            node_id: 12,
+            proto_ver: 1,
+            flags: SyncPacketFlags { is_leader: true, is_valid: true, smoothed_used: false },
+            local_us: 28_864_932,
+            epoch_us: 28_864_939,
+            sequence: 20,
+        };
+        let wire = pkt.to_bytes();
+        let decoded = SyncPacket::from_bytes(&wire).unwrap();
+        assert_eq!(decoded.flags.to_byte(), 0x03);
+        assert_eq!(decoded.local_minus_epoch_us(), -7);  // leader has zero offset modulo call-stack
+        assert!(decoded.flags.is_leader);
+        assert!(decoded.flags.is_valid);
+        assert!(!decoded.flags.smoothed_used);
+    }
+
+    #[test]
+    fn magic_mismatch_is_typed_error() {
+        let mut wire = SyncPacket {
+            node_id: 1, proto_ver: 1, flags: SyncPacketFlags::default(),
+            local_us: 0, epoch_us: 0, sequence: 0,
+        }.to_bytes();
+        wire[0] = 0x01;  // corrupt magic low byte
+        let err = SyncPacket::from_bytes(&wire).unwrap_err();
+        match err {
+            ParseError::InvalidMagic { got, .. } => assert_ne!(got, SYNC_PACKET_MAGIC),
+            other => panic!("expected InvalidMagic, got {other:?}"),
+        }
+    }
+
+    #[test]
+    fn short_packet_is_typed_error() {
+        let wire = [0u8; 16];  // half a packet
+        let err = SyncPacket::from_bytes(&wire).unwrap_err();
+        match err {
+            ParseError::InsufficientData { needed, got } => {
+                assert_eq!(needed, SYNC_PACKET_SIZE);
+                assert_eq!(got, 16);
+            }
+            other => panic!("expected InsufficientData, got {other:?}"),
+        }
+    }
+
+    /// Every (leader, valid, smoothed_used) triple round-trips independently.
+    #[test]
+    fn all_flag_combinations_roundtrip() {
+        for &is_leader in &[false, true] {
+            for &is_valid in &[false, true] {
+                for &smoothed_used in &[false, true] {
+                    let flags = SyncPacketFlags { is_leader, is_valid, smoothed_used };
+                    let pkt = SyncPacket {
+                        node_id: 1, proto_ver: 1, flags,
+                        local_us: 1234, epoch_us: 5678, sequence: 99,
+                    };
+                    let wire = pkt.to_bytes();
+                    let decoded = SyncPacket::from_bytes(&wire).unwrap();
+                    assert_eq!(decoded.flags, flags);
+                    assert_eq!(decoded.flags.to_byte(), flags.to_byte());
+                }
+            }
+        }
+    }
+
+    /// A host dispatches CSI vs sync purely on the leading u32. The two
+    /// magics must therefore never collide.
+    #[test]
+    fn sync_and_csi_magics_differ() {
+        assert_ne!(SYNC_PACKET_MAGIC, crate::esp32_parser::ESP32_CSI_MAGIC);
+    }
+
+    #[test]
+    fn wire_size_constant_is_correct() {
+        let pkt = SyncPacket {
+            node_id: 0, proto_ver: 1, flags: SyncPacketFlags::default(),
+            local_us: 0, epoch_us: 0, sequence: 0,
+        };
+        assert_eq!(pkt.to_bytes().len(), SYNC_PACKET_SIZE);
+        assert_eq!(SYNC_PACKET_SIZE, 32);
+    }
+}