diff --git a/tines-core/src/belief.rs b/tines-core/src/belief.rs
index 7bc4c948..7e7deb4c 100644
--- a/tines-core/src/belief.rs
+++ b/tines-core/src/belief.rs
@@ -108,6 +108,7 @@ mod tests {
             topic: Topic::from_slice(b"door/3").unwrap(),
             payload: Payload::from_slice(b"open").unwrap(),
             dest: None,
+            sig: None,
         }
     }
 
diff --git a/tines-core/src/consts.rs b/tines-core/src/consts.rs
index ccb71a76..7dd2e4e0 100644
--- a/tines-core/src/consts.rs
+++ b/tines-core/src/consts.rs
@@ -18,6 +18,11 @@ pub const MAX_TOPIC: usize = 64;
 /// Maximum payload length in bytes.
 pub const MAX_PAYLOAD: usize = 1024;
 
+/// Maximum signature length in bytes. The 1.0 signature slot reserves this on
+/// every observation (`[crate::observation::Signature]`); it is carried verbatim
+/// and never signed or verified until 1.1.
+pub const MAX_SIG: usize = 64;
+
 /// Maximum number of peers a node tracks.
 pub const MAX_PEERS: usize = 8;
 
@@ -36,6 +41,12 @@ pub const REASSEMBLY_TIMEOUT_MS: u64 = 5000;
 /// Maximum number of frames buffered for outbound delivery.
 pub const SEND_QUEUE_CAP: usize = 256;
 
+/// Minimum usable UDP frame size in bytes (the BLE floor below which a
+/// fragment header leaves no room for payload). [`crate::frag::fragment`] gives
+/// up cleanly with `WireError::TooLarge` for any `mtu` below this rather than
+/// emitting a truncated frame; the MTU sweep runs from here to [`MAX_FRAME`].
+pub const MIN_MTU: usize = 23;
+
 /// Maximum UDP frame size in bytes.
 pub const MAX_FRAME: usize = 1500;
 
diff --git a/tines-core/src/exchange.rs b/tines-core/src/exchange.rs
index 3187c704..e3f08d79 100644
--- a/tines-core/src/exchange.rs
+++ b/tines-core/src/exchange.rs
@@ -1292,6 +1292,7 @@ mod tests {
             topic: Topic::from_slice(topic).unwrap(),
             payload: Payload::from_slice(payload).unwrap(),
             dest: None,
+            sig: None,
         }
     }
 
diff --git a/tines-core/src/frag.rs b/tines-core/src/frag.rs
index 8a8dde70..61d66f74 100644
--- a/tines-core/src/frag.rs
+++ b/tines-core/src/frag.rs
@@ -218,6 +218,113 @@ mod tests {
             topic: Topic::from_slice(b"door/3").unwrap(),
             payload: Payload::from_slice(&std::vec![0u8; payload_len]).unwrap(),
             dest: None,
+            sig: None,
+        }
+    }
+
+    fn signed_max_obs(sig: crate::Signature) -> Observation {
+        let mut obs = obs_with_payload([1; 16], consts::MAX_PAYLOAD);
+        obs.sig = Some(sig);
+        obs
+    }
+
+    #[test]
+    fn reassembled_bad_signature_is_malformed() {
+        // A maximum-size signed obs carrying a malformed Ed25519 signature (wrong
+        // length) must be rejected on reassembly — never returned — exactly as a
+        // single-frame decode would reject it.
+        let obs = signed_max_obs(crate::Signature {
+            version: 1,
+            algo: crate::SigAlgo::Ed25519,
+            bytes: heapless::Vec::from_slice(&[0u8; 63]).unwrap(),
+        });
+        let mut frames: Vec<Vec<u8>> = Vec::new();
+        fragment([1; 16], &obs, 200, &mut |b| frames.push(b.to_vec()))
+            .expect("fragment signed max obs");
+        let mut r = Reassembler::new();
+        let mut last: Option<Observation> = None;
+        for f in frames.iter() {
+            if let Frame::Frag {
+                id,
+                index,
+                count,
+                data,
+                ..
+            } = Frame::decode(f).unwrap()
+            {
+                last = r.feed(id, index, count, &data, 0);
+            }
+        }
+        assert!(
+            last.is_none(),
+            "a malformed signature on reassembly must be rejected, never returned"
+        );
+    }
+
+    #[test]
+    fn reassembled_unknown_algo_signature_roundtrips() {
+        // An unknown-algorithm signature is carried verbatim on reassembly too.
+        let obs = signed_max_obs(crate::Signature {
+            version: 2,
+            algo: crate::SigAlgo::Unknown(7),
+            bytes: heapless::Vec::from_slice(&[9u8; 10]).unwrap(),
+        });
+        let mut frames: Vec<Vec<u8>> = Vec::new();
+        fragment([1; 16], &obs, 200, &mut |b| frames.push(b.to_vec()))
+            .expect("fragment signed max obs");
+        let mut r = Reassembler::new();
+        let mut last: Option<Observation> = None;
+        for f in frames.iter() {
+            if let Frame::Frag {
+                id,
+                index,
+                count,
+                data,
+                ..
+            } = Frame::decode(f).unwrap()
+            {
+                last = r.feed(id, index, count, &data, 0);
+            }
+        }
+        assert_eq!(last, Some(obs), "unknown-algo sig must reassemble verbatim");
+    }
+
+    #[test]
+    fn fragmentation_fits_mtu_sweep() {
+        // Review Focus #6: a full-size signed obs (MAX_PAYLOAD + 64-byte Ed25519
+        // sig) must fragment into <= MAX_FRAGMENTS frames each <= mtu, or — below
+        // the BLE floor — be given up cleanly as TooLarge, never emitted
+        // oversized, across every mtu from MIN_MTU to MAX_FRAME.
+        let obs = signed_max_obs(crate::Signature {
+            version: 1,
+            algo: crate::SigAlgo::Ed25519,
+            bytes: heapless::Vec::from_slice(&[0u8; 64]).unwrap(),
+        });
+        for mtu in consts::MIN_MTU..=consts::MAX_FRAME {
+            let mut frames: Vec<Vec<u8>> = Vec::new();
+            match fragment([1; 16], &obs, mtu, &mut |b| frames.push(b.to_vec())) {
+                Ok(count) => {
+                    assert!(
+                        count <= MAX_FRAGMENTS,
+                        "frame count {count} exceeds MAX_FRAGMENTS {MAX_FRAGMENTS}"
+                    );
+                    assert_eq!(frames.len(), count, "emit count must match at mtu {mtu}");
+                    for f in &frames {
+                        assert!(
+                            f.len() <= mtu,
+                            "frame of {} bytes exceeds mtu {mtu}",
+                            f.len()
+                        );
+                    }
+                }
+                Err(crate::wire::WireError::TooLarge) => {
+                    assert!(
+                        frames.is_empty(),
+                        "TooLarge at mtu {mtu} must emit no frames"
+                    );
+                }
+                Err(other) => panic!("unexpected error {other:?} at mtu {mtu}"),
+            }
         }
     }
 
diff --git a/tines-core/src/lib.rs b/tines-core/src/lib.rs
index 39ef5f30..49bee3b0 100644
--- a/tines-core/src/lib.rs
+++ b/tines-core/src/lib.rs
@@ -22,7 +22,9 @@ pub use bloom::Bloom;
 pub use exchange::{DropReason, Exchange, NodeEvent, Peer};
 pub use frag::{fragment, Reassembler};
 pub use node::{Node, ObserveError};
-pub use observation::{Dest, NodeId, Observation, ObservationId, Payload, Tick, Topic};
+pub use observation::{
+    Dest, NodeId, Observation, ObservationId, Payload, SigAlgo, Signature, Tick, Topic,
+};
 pub use store::{Store, StoreError, TrimPolicy};
 pub use transport::{Event, FrameBuf, SendError, Transport};
 pub use wire::{Frame, WireError};
diff --git a/tines-core/src/mem_store.rs b/tines-core/src/mem_store.rs
index 39d9b0d0..dc9bfd1a 100644
--- a/tines-core/src/mem_store.rs
+++ b/tines-core/src/mem_store.rs
@@ -215,6 +215,7 @@ mod tests {
             topic: Topic::from_slice(topic).unwrap(),
             payload: Payload::from_slice(b"").unwrap(),
             dest: None,
+            sig: None,
         }
     }
 
diff --git a/tines-core/src/node.rs b/tines-core/src/node.rs
index 7646b259..03584871 100644
--- a/tines-core/src/node.rs
+++ b/tines-core/src/node.rs
@@ -92,6 +92,7 @@ impl<S: Store, T: Transport> Node<S, T> {
             topic,
             payload,
             dest: None,
+            sig: None,
         };
         self.next_seq += 1;
         let id = obs.id();
@@ -128,6 +129,7 @@ impl<S: Store, T: Transport> Node<S, T> {
             topic,
             payload,
             dest: Some(Dest { to, lifetime_ms }),
+            sig: None,
         };
         self.next_seq += 1;
         let id = obs.id();
diff --git a/tines-core/src/observation.rs b/tines-core/src/observation.rs
index b6f7b6cd..eae682e0 100644
--- a/tines-core/src/observation.rs
+++ b/tines-core/src/observation.rs
@@ -3,6 +3,7 @@
 use crate::consts;
 use blake2::{Blake2s256, Digest};
 use heapless::Vec;
+use serde::de::Deserializer;
 use serde::{Deserialize, Serialize};
 
 /// 16-byte node identifier.
@@ -55,6 +56,13 @@ pub struct Observation {
     /// Addressing: `None` is a broadcast, `Some(dest)` is addressed to
     /// `dest.to` and expires per `dest.lifetime_ms`.
     pub dest: Option<Dest>,
+
+    /// The observer's signature over this observation, if any.
+    ///
+    /// The 1.0 wire reserves this slot on every observation and carries a
+    /// signature verbatim (see [`Signature`] / [`SigAlgo`]), but 1.0 does not sign
+    /// or verify it. Signing and verification arrive in 1.1.
+    pub sig: Option<Signature>,
 }
 
 impl Observation {
@@ -103,6 +111,7 @@ impl Observation {
             topic: self.topic.clone(),
             payload: self.payload.clone(),
             dest: self.dest.clone(),
+            sig: self.sig.clone(),
         }
     }
 
@@ -118,6 +127,7 @@ impl Observation {
             topic: Topic::from_slice(topic).expect("topic fits MAX_TOPIC"),
             payload: Payload::from_slice(payload).expect("payload fits MAX_PAYLOAD"),
             dest: None,
+            sig: None,
         }
     }
 
@@ -141,6 +151,7 @@ impl Observation {
             topic: Topic::from_slice(topic).expect("topic fits MAX_TOPIC"),
             payload: Payload::from_slice(payload).expect("payload fits MAX_PAYLOAD"),
             dest: Some(Dest { to, lifetime_ms }),
+            sig: None,
         }
     }
 
@@ -152,6 +163,115 @@ impl Observation {
     }
 }
 
+/// A signature scheme identifier, carried in [`Signature::algo`].
+///
+/// On the wire `algo` is a raw `u8` — the `#[repr(u8)]` discriminant, *not* a
+/// postcard enum tag: [`SigAlgo::Ed25519`] is the byte `1`, and an algorithm
+/// `tines-core` does not recognize is carried as [`SigAlgo::Unknown`] with its
+/// raw id, never rejected. `0` is never valid here (it is `Malformed` on decode).
+///
+/// Signing and verification arrive in 1.1.
+#[non_exhaustive]
+#[repr(u8)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum SigAlgo {
+    /// Ed25519: a 64-byte Ed25519 signature.
+    Ed25519 = 1,
+    /// An algorithm id `tines-core` does not recognize, carried verbatim.
+    /// Any `u8` other than `0` (the malformed sentinel) and `1` (`Ed25519`) is
+    /// preserved so a 1.0 node can forward it untouched to a 1.1 node.
+    Unknown(u8),
+}
+
+/// An observation's signature: the observer's over the whole observation.
+///
+/// The slot is reserved on the 1.0 wire but *unsigned* in 1.0: this type only
+/// carries a signature verbatim, enforcing the shape rules below on decode.
+/// Signing and verification arrive in 1.1.
+#[non_exhaustive]
+#[derive(Clone, Debug, PartialEq, Eq, Serialize)]
+pub struct Signature {
+    /// Signature format version. `0` is rejected as `Malformed` on decode;
+    /// every other value (including any version `tines-core` does not know) is
+    /// carried verbatim.
+    pub version: u8,
+    /// The algorithm the signature is over. Serialized as a raw `u8` on the
+    /// wire (its `#[repr(u8)]` discriminant, so [`SigAlgo::Ed25519`] is `1`);
+    /// unknown ids are preserved as [`SigAlgo::Unknown`] rather than rejected.
+    #[serde(with = "sig_algo_wire")]
+    pub algo: SigAlgo,
+    /// The signature bytes. For [`SigAlgo::Ed25519`] these MUST be exactly 64
+    /// bytes (a different length is `Malformed`); other algorithms carry any
+    /// length. Never rejected for being unparseable — carried as-is.
+    pub bytes: heapless::Vec<u8, { consts::MAX_SIG }>,
+}
+
+impl<'de> Deserialize<'de> for Signature {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        #[derive(Deserialize)]
+        struct RawSignature {
+            version: u8,
+            #[serde(with = "sig_algo_wire")]
+            algo: SigAlgo,
+            bytes: heapless::Vec<u8, { consts::MAX_SIG }>,
+        }
+        let raw = RawSignature::deserialize(deserializer)?;
+        // A malformed signature (bad version, bad or wrong-length algorithm) is
+        // carried by no frame: it is a decode failure, never a panic.
+        if raw.version == 0 {
+            return Err(serde::de::Error::custom("signature version 0 is malformed"));
+        }
+        if matches!(raw.algo, SigAlgo::Ed25519) && raw.bytes.len() != 64 {
+            return Err(serde::de::Error::custom(
+                "Ed25519 signature must be exactly 64 bytes",
+            ));
+        }
+        Ok(Signature {
+            version: raw.version,
+            algo: raw.algo,
+            bytes: raw.bytes,
+        })
+    }
+}
+
+/// Wire encoding of [`SigAlgo`]: a raw `u8` (its `#[repr(u8)]` discriminant),
+/// not a postcard enum tag. Used via `#[serde(with = "sig_algo_wire")]` on the
+/// [`Signature::algo`] field so an unknown id survives decode as [`SigAlgo::Unknown`].
+mod sig_algo_wire {
+    use super::SigAlgo;
+    use serde::de::Deserializer;
+    use serde::ser::Serializer;
+    use serde::Deserialize;
+
+    pub fn serialize<S>(algo: &SigAlgo, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        match algo {
+            // `Ed25519` is the byte `1`; any carried `Unknown(n)` is its raw id.
+            SigAlgo::Ed25519 => serializer.serialize_u8(1),
+            SigAlgo::Unknown(id) => serializer.serialize_u8(*id),
+        }
+    }
+
+    pub fn deserialize<'de, D>(deserializer: D) -> Result<SigAlgo, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        let raw = u8::deserialize(deserializer)?;
+        // `0` is the malformed sentinel on the wire; `1` is `Ed25519`; every
+        // other id is carried as `Unknown(n)` so it forwards untouched.
+        match raw {
+            0 => Err(serde::de::Error::custom("signature algo id 0 is malformed")),
+            1 => Ok(SigAlgo::Ed25519),
+            id => Ok(SigAlgo::Unknown(id)),
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -165,9 +285,31 @@ mod tests {
             topic: Topic::from_slice(b"door/3").unwrap(),
             payload: Payload::from_slice(b"open").unwrap(),
             dest,
+            sig: None,
         }
     }
 
+    fn sig(version: u8, algo: SigAlgo, bytes: &[u8]) -> Signature {
+        Signature {
+            version,
+            algo,
+            bytes: Vec::from_slice(bytes).unwrap(),
+        }
+    }
+
+    #[test]
+    fn sig_excluded_from_id() {
+        // A signature must not affect identity: a bare, a full Ed25519 and an
+        // arbitrary unknown-algorithm sig all share the observation's id.
+        let base = obs(5, 0, None, None);
+        let mut signed = obs(5, 0, None, None);
+        signed.sig = Some(sig(1, SigAlgo::Ed25519, &[0u8; 64]));
+        assert_eq!(base.id(), signed.id(), "sig must not affect id");
+        let mut other = obs(5, 0, None, None);
+        other.sig = Some(sig(2, SigAlgo::Unknown(9), &[1u8; 10]));
+        assert_eq!(base.id(), other.id());
+    }
+
     #[test]
     fn id_ignores_age_and_observed_at() {
         assert_eq!(obs(1, 0, None, None).id(), obs(1, 999, Some(5), None).id());
@@ -360,4 +502,47 @@ mod tests {
             ]
         );
     }
+
+    #[test]
+    fn sig_algo_wire_roundtrip() {
+        // Review Focus #3: the raw-u8 wire encoding round-trips a known Ed25519
+        // and every unknown id verbatim, rejects the malformed sentinel, and
+        // never maps a wire byte of 1 to Unknown(1). Exercises the algo field
+        // through Signature, since SigAlgo serializes only via its serde module.
+        let make = |algo: SigAlgo| Signature {
+            version: 1,
+            algo,
+            bytes: heapless::Vec::<u8, { crate::consts::MAX_SIG }>::from_slice(&[0u8; 64]).unwrap(),
+        };
+        for (algo, wire_byte) in [
+            (SigAlgo::Ed25519, 1u8),
+            (SigAlgo::Unknown(7), 7u8),
+            (SigAlgo::Unknown(255), 255u8),
+        ] {
+            let sig = make(algo);
+            let mut buf = [0u8; consts::MAX_SIG + 8];
+            let n = postcard::to_slice(&sig, &mut buf).unwrap();
+            assert_eq!(n[0], 1, "version serializes as the first byte");
+            assert_eq!(n[1], wire_byte, "algo is its raw repr discriminant");
+            let decoded: Signature = postcard::from_bytes(&n[..]).unwrap();
+            assert_eq!(decoded.algo, algo, "algo must round-trip verbatim");
+        }
+        // `0` is the malformed sentinel on the wire — it must fail to decode.
+        let sig = make(SigAlgo::Unknown(0));
+        let mut buf = [0u8; consts::MAX_SIG + 8];
+        let n = postcard::to_slice(&sig, &mut buf).unwrap();
+        assert_eq!(n[1], 0);
+        let bad: Result<Signature, _> = postcard::from_bytes::<Signature>(n);
+        assert!(bad.is_err(), "algo id 0 must be malformed");
+        // A wire byte of 1 is Ed25519, never Unknown(1).
+        let sig = make(SigAlgo::Ed25519);
+        let mut buf = [0u8; consts::MAX_SIG + 8];
+        let n = postcard::to_slice(&sig, &mut buf).unwrap();
+        assert_eq!(n[1], 1);
+        assert_eq!(
+            postcard::from_bytes::<Signature>(n).unwrap().algo,
+            SigAlgo::Ed25519,
+            "wire byte 1 must decode to Ed25519"
+        );
+    }
 }
diff --git a/tines-core/src/wire.rs b/tines-core/src/wire.rs
index 93b9b173..57c38535 100644
--- a/tines-core/src/wire.rs
+++ b/tines-core/src/wire.rs
@@ -126,8 +126,7 @@ pub enum WireError {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::Payload;
-    use crate::Topic;
+    use crate::{Payload, SigAlgo, Signature, Topic};
 
     fn obs_frame() -> Frame {
         Frame::Obs {
@@ -140,6 +139,7 @@ mod tests {
                 topic: Topic::from_slice(b"door/3").unwrap(),
                 payload: Payload::from_slice(b"open").unwrap(),
                 dest: None,
+                sig: None,
             },
         }
     }
@@ -155,6 +155,7 @@ mod tests {
                 topic: Topic::from_slice(b"t").unwrap(),
                 payload: Payload::from_slice(&[0u8; 1024]).unwrap(),
                 dest: None,
+                sig: None,
             },
         }
     }
@@ -476,4 +477,208 @@ mod tests {
         let mut buf = [0u8; 16];
         assert_eq!(f.encode(&mut buf).err(), Some(WireError::TooLarge));
     }
+
+    fn sig(version: u8, algo: SigAlgo, bytes: &[u8]) -> Signature {
+        Signature {
+            version,
+            algo,
+            bytes: Vec::from_slice(bytes).unwrap(),
+        }
+    }
+
+    fn signed_obs(sig: Signature) -> Observation {
+        Observation {
+            observer: [7; 16],
+            seq: 42,
+            age_ms: 123,
+            observed_at: Some(999),
+            topic: Topic::from_slice(b"door/3").unwrap(),
+            payload: Payload::from_slice(b"open").unwrap(),
+            dest: None,
+            sig: Some(sig),
+        }
+    }
+
+    #[test]
+    fn obs_roundtrip_with_ed25519_signature() {
+        let f = Frame::Obs {
+            from: [7; 16],
+            obs: signed_obs(sig(1, SigAlgo::Ed25519, &[0u8; 64])),
+        };
+        let mut buf = [0u8; consts::MAX_FRAME];
+        let n = f.encode(&mut buf).unwrap();
+        let decoded = Frame::decode(&buf[..n]).unwrap();
+        assert_eq!(f, decoded);
+    }
+
+    #[test]
+    fn obs_roundtrip_with_unknown_algo() {
+        // An unknown algorithm id with short bytes is carried verbatim.
+        let f = Frame::Obs {
+            from: [7; 16],
+            obs: signed_obs(sig(2, SigAlgo::Unknown(7), &[9u8; 10])),
+        };
+        let mut buf = [0u8; consts::MAX_FRAME];
+        let n = f.encode(&mut buf).unwrap();
+        let decoded = Frame::decode(&buf[..n]).unwrap();
+        assert_eq!(f, decoded);
+    }
+
+    #[test]
+    fn algo_zero_is_malformed() {
+        let f = Frame::Obs {
+            from: [7; 16],
+            obs: signed_obs(sig(1, SigAlgo::Unknown(0), &[0u8; 64])),
+        };
+        let mut buf = [0u8; consts::MAX_FRAME];
+        let n = f.encode(&mut buf).unwrap();
+        assert_eq!(Frame::decode(&buf[..n]).err(), Some(WireError::Malformed));
+    }
+
+    #[test]
+    fn version_zero_is_malformed() {
+        let f = Frame::Obs {
+            from: [7; 16],
+            obs: signed_obs(sig(0, SigAlgo::Ed25519, &[0u8; 64])),
+        };
+        let mut buf = [0u8; consts::MAX_FRAME];
+        let n = f.encode(&mut buf).unwrap();
+        assert_eq!(Frame::decode(&buf[..n]).err(), Some(WireError::Malformed));
+    }
+
+    #[test]
+    fn ed25519_wrong_length_is_malformed() {
+        let f = Frame::Obs {
+            from: [7; 16],
+            obs: signed_obs(sig(1, SigAlgo::Ed25519, &[0u8; 63])),
+        };
+        let mut buf = [0u8; consts::MAX_FRAME];
+        let n = f.encode(&mut buf).unwrap();
+        assert_eq!(Frame::decode(&buf[..n]).err(), Some(WireError::Malformed));
+    }
+
+    #[test]
+    fn raw_one_decodes_to_ed25519() {
+        // A wire algo byte of 1 must decode to Ed25519, never Unknown(1).
+        let f = Frame::Obs {
+            from: [7; 16],
+            obs: signed_obs(sig(1, SigAlgo::Unknown(1), &[0u8; 64])),
+        };
+        let mut buf = [0u8; consts::MAX_FRAME];
+        let n = f.encode(&mut buf).unwrap();
+        let decoded = Frame::decode(&buf[..n]).unwrap();
+        match decoded {
+            Frame::Obs { obs, .. } => {
+                assert_eq!(obs.sig.as_ref().unwrap().algo, SigAlgo::Ed25519);
+            }
+            other => panic!("expected Obs, got {other:?}"),
+        }
+    }
+
+    // Pinned wire vector for a full-size (MAX_PAYLOAD + 64-byte Ed25519) signed
+    // Observation, exactly as a 1.0 node would emit it: the golden vector for
+    // review focus #5. Decoding it must yield the bare Observation with a
+    // SigAlgo::Ed25519 carrying 64 zeroed signature bytes.
+    const OBS_GOLDEN_VECTOR_ED25519: [u8; 1139] = [
+        0x04, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
+        0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
+        0x01, 0x01, 0x01, 0x01, 0x01, 0x00, 0x00, 0x06, 0x64, 0x6f, 0x6f, 0x72, 0x2f, 0x33, 0x80,
+        0x08, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01, 0x01, 0x40, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+        0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+    ];
+
+    #[test]
+    fn golden_vector_ed25519_decodes_to_bare_obs() {
+        // Review Focus #5: the pinned vector is the golden Obs vector — decoding
+        // it must yield the bare Observation with an Ed25519 signature carrying
+        // 64 zeroed bytes.
+        let frame = Frame::decode(&OBS_GOLDEN_VECTOR_ED25519).unwrap();
+        let Frame::Obs { from, obs } = frame else {
+            panic!("expected an Obs frame")
+        };
+        assert_eq!(from, [1; 16]);
+        assert_eq!(obs.observer, [1; 16]);
+        assert_eq!(obs.seq, 1);
+        assert_eq!(obs.age_ms, 0);
+        assert_eq!(obs.observed_at, None);
+        assert_eq!(&obs.topic[..], b"door/3");
+        assert_eq!(obs.payload.len(), consts::MAX_PAYLOAD);
+        assert_eq!(obs.dest, None);
+        let sig = obs.sig.expect("a signed obs carries a signature");
+        assert_eq!(sig.version, 1);
+        assert_eq!(sig.algo, SigAlgo::Ed25519);
+        assert_eq!(sig.bytes.len(), 64);
+        assert!(sig.bytes.iter().all(|b| *b == 0));
+    }
 }
diff --git a/tines-store/src/log.rs b/tines-store/src/log.rs
index 44cdf203..090fe73a 100644
--- a/tines-store/src/log.rs
+++ b/tines-store/src/log.rs
@@ -1024,6 +1024,7 @@ mod tests {
             topic: tines_core::Topic::from_slice(b"door/3").unwrap(),
             payload: tines_core::Payload::from_slice(b"open").unwrap(),
             dest: None,
+            sig: None,
         }
     }
 
diff --git a/tines-store/tests/persistence.rs b/tines-store/tests/persistence.rs
index 4a7ebf52..14545891 100644
--- a/tines-store/tests/persistence.rs
+++ b/tines-store/tests/persistence.rs
@@ -21,6 +21,7 @@ fn obs(observer: [u8; 16], seq: u64, age: u64, at: Option<u64>) -> Observation {
         topic: Topic::from_slice(b"door/3").unwrap(),
         payload: Payload::from_slice(b"open").unwrap(),
         dest: None,
+        sig: None,
     }
 }
 
@@ -346,6 +347,7 @@ mod fleet_fixes_f5 {
             topic: Topic::from_slice(b"door/3").unwrap(),
             payload: Payload::from_slice(b"open").unwrap(),
             dest: None,
+            sig: None,
         }
     }