refactor(core): make Frame and WireError crate-private

Spec §3 (decision D-b) lists `Frame` and `WireError` as private; lib.rs
re-exported both. Only `frame_sender` stays public.

- The pinned vectors in tests/vectors.rs now compile in-crate as a
  `#[cfg(test)] #[path]` module (autotests = false keeps Cargo from also
  building them as an integration test). Every golden vector now checks
  `encode() == GOLDEN` as well as the decode, and new literal vectors pin a
  trailing-byte rejection and an addressed Obs with a nonzero age and an
  `observed_at`.
- A `#[doc(hidden)]` `conformance` module (behind the `conformance`
  feature) gives the fuzz harness byte-level frame encoders/decoders and
  core's local limits without exposing `Frame`. The fuzz_twin test target
  now requires `conformance`, which scripts/ci.sh enables.
- compile_fail doctests pin that `Frame`/`WireError` are unreachable.
- Remove the THROWAWAY gen_missing_golden_vectors test and fix stale
  wire.rs comments about the version/tag byte offsets.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tines-core/Cargo.toml

@@ -11,6 +11,10 @@ readme.workspace = true
 documentation = "https://docs.rs/tines-core"
 keywords = ["robotics", "gossip", "delay-tolerant", "no-std", "sync"]
 categories = ["no-std", "embedded", "network-programming", "science::robotics"]
+# Test targets are listed by hand below: `tests/vectors.rs` is not one. It pins
+# the wire format against the crate-private `Frame`, so `src/lib.rs` compiles
+# it into the unit tests instead (`#[path = "../tests/vectors.rs"]`).
+autotests = false
 
 [features]
 default = ["alloc"]
@@ -19,6 +23,8 @@ alloc = []
 # backends run against themselves to prove they honor the `Store` contract.
 # Std-free so it builds with `--no-default-features`; enabled only by the
 # backend crates that exercise the suite (MemStore, LogStore, CappedStore).
+# It also turns on the `#[doc(hidden)]` `conformance` module, which gives the
+# fuzz harness byte-level frame helpers and core's local limits.
 conformance = []
 
 [dependencies]
@@ -33,3 +39,16 @@ proptest = "1"
 # the test suite via a `#[path]` module include to keep it the SAME harness.
 # That source names `heapless` directly, so restate it here for the twin.
 heapless = { version = "0.8", features = ["serde"] }
+
+[[test]]
+name = "pair"
+
+[[test]]
+name = "public_api"
+
+# The proptest twin of the `fuzz/` harness builds frames through the hidden
+# `conformance` helpers, so it runs only with that feature (as `scripts/ci.sh`
+# does) and needs `MemStore` (`alloc`).
+[[test]]
+name = "fuzz_twin"
+required-features = ["alloc", "conformance"]

tines-core/src/conformance.rs

@@ -0,0 +1,144 @@
+//! Test-only hooks into crate-private wire types and local constants.
+//!
+//! **Not public API.** Hidden from the docs, behind the `conformance`
+//! feature, and outside the 1.x stability promise: anything here may change
+//! or vanish in any release.
+//!
+//! `Frame` and `WireError` are crate-private (spec §3), and the local
+//! capacities and timings are `pub(crate)` (decision K). The fuzz harness in
+//! `fuzz/` and its proptest twin (`tines-core/tests/fuzz_twin.rs`) still need
+//! to build well-formed frames, read the frames a `Node` sends, and size
+//! their scenarios by core's local limits. These functions give them exactly
+//! that, as byte-level helpers, without exposing the `Frame` enum.
+//!
+//! Every function is `no_std`, allocation-free and panic-free on any input.
+
+use crate::consts;
+use crate::wire::Frame;
+use crate::{NodeId, Observation, ObservationId, SigAlgo, Signature};
+
+/// Core's local peer-table capacity (`consts::MAX_PEERS`).
+pub const MAX_PEERS: usize = consts::MAX_PEERS;
+/// Core's idle-eviction window (`consts::PEER_IDLE_MS`).
+pub const PEER_IDLE_MS: u64 = consts::PEER_IDLE_MS;
+/// Core's summary cadence (`consts::SUMMARY_INTERVAL_MS`).
+pub const SUMMARY_INTERVAL_MS: u64 = consts::SUMMARY_INTERVAL_MS;
+/// Core's per-peer send-queue and bounce-table capacity (`consts::SEND_QUEUE_CAP`).
+pub const SEND_QUEUE_CAP: usize = consts::SEND_QUEUE_CAP;
+/// Core's `Delivered` event-queue capacity (`consts::EVENT_QUEUE_CAP`).
+pub const EVENT_QUEUE_CAP: usize = consts::EVENT_QUEUE_CAP;
+/// Core's MTU-sweep lower bound (`consts::MIN_MTU`).
+pub const MIN_MTU: usize = consts::MIN_MTU;
+/// Bytes a `Frag` frame may add around its data (`frag::FRAG_OVERHEAD`).
+pub const FRAG_OVERHEAD: usize = crate::frag::FRAG_OVERHEAD;
+/// Most fragments one observation may be split into (`frag::MAX_FRAGMENTS`).
+pub const MAX_FRAGMENTS: usize = crate::frag::MAX_FRAGMENTS;
+
+fn encode(frame: &Frame, out: &mut [u8]) -> Option<usize> {
+    frame.encode(out).ok()
+}
+
+/// Encodes a `Summary` frame into `out`. `None` if `bits` is longer than
+/// `SUMMARY_BYTES` or `out` is too small.
+pub fn encode_summary(from: NodeId, salt: u32, bits: &[u8], out: &mut [u8]) -> Option<usize> {
+    let bits = heapless::Vec::from_slice(bits).ok()?;
+    encode(&Frame::Summary { from, salt, bits }, out)
+}
+
+/// Encodes an `Obs` frame carrying `obs` into `out`. `None` if `out` is too
+/// small.
+pub fn encode_obs(from: NodeId, obs: &Observation, out: &mut [u8]) -> Option<usize> {
+    let obs = obs.clone();
+    encode(&Frame::Obs { from, obs }, out)
+}
+
+/// Encodes a `Frag` frame into `out`. `None` if `data` is longer than
+/// `MAX_FRAME` or `out` is too small. `index`/`count` are not validated: an
+/// adversarial harness sends inconsistent ones on purpose.
+pub fn encode_frag(
+    from: NodeId,
+    id: ObservationId,
+    index: u8,
+    count: u8,
+    data: &[u8],
+    out: &mut [u8],
+) -> Option<usize> {
+    let data = heapless::Vec::from_slice(data).ok()?;
+    encode(
+        &Frame::Frag {
+            from,
+            id,
+            index,
+            count,
+            data,
+        },
+        out,
+    )
+}
+
+/// Encodes an `Ack` frame into `out`. `None` if `ids` is longer than
+/// `ACK_IDS_CAP` or `out` is too small.
+pub fn encode_ack(from: NodeId, ids: &[ObservationId], out: &mut [u8]) -> Option<usize> {
+    let ids = heapless::Vec::from_slice(ids).ok()?;
+    encode(&Frame::Ack { from, ids }, out)
+}
+
+/// Encodes `obs` alone (no frame envelope) into `out`: the byte stream a
+/// sender cuts into `Frag` data. `None` if `out` is too small.
+pub fn encode_observation(obs: &Observation, out: &mut [u8]) -> Option<usize> {
+    postcard::to_slice(obs, out).ok().map(|s| s.len())
+}
+
+/// The sender of `bytes` if they decode as a complete, canonical frame — the
+/// same decode the exchange runs — else `None` (the exchange counts such a
+/// frame as `VersionMismatch` or `Malformed`).
+pub fn decoded_sender(bytes: &[u8]) -> Option<NodeId> {
+    Frame::decode(bytes).ok().map(|f| f.sender())
+}
+
+/// The observation in `bytes` if they decode as an `Obs` frame.
+pub fn obs_of(bytes: &[u8]) -> Option<Observation> {
+    match Frame::decode(bytes).ok()? {
+        Frame::Obs { obs, .. } => Some(obs),
+        _ => None,
+    }
+}
+
+/// `(id, index, count)` of `bytes` if they decode as a `Frag` frame.
+pub fn frag_of(bytes: &[u8]) -> Option<(ObservationId, u8, u8)> {
+    match Frame::decode(bytes).ok()? {
+        Frame::Frag {
+            id, index, count, ..
+        } => Some((id, index, count)),
+        _ => None,
+    }
+}
+
+/// Calls `f` on each id of `bytes` if they decode as an `Ack` frame, and
+/// returns whether they did.
+pub fn ack_of(bytes: &[u8], f: &mut dyn FnMut(&ObservationId)) -> bool {
+    match Frame::decode(bytes) {
+        Ok(Frame::Ack { ids, .. }) => {
+            ids.iter().for_each(f);
+            true
+        }
+        _ => false,
+    }
+}
+
+/// Whether `bytes` decode as a `Summary` frame.
+pub fn is_summary(bytes: &[u8]) -> bool {
+    matches!(Frame::decode(bytes), Ok(Frame::Summary { .. }))
+}
+
+/// Builds a [`Signature`] (a `#[non_exhaustive]` struct only core can
+/// construct). `None` if `bytes` is longer than `MAX_SIG`. The shape rules
+/// (version `0`, a non-64-byte Ed25519) are not checked: a harness builds
+/// invalid signatures on purpose to see them rejected on decode.
+pub fn signature(version: u8, algo: SigAlgo, bytes: &[u8]) -> Option<Signature> {
+    Some(Signature {
+        version,
+        algo,
+        bytes: heapless::Vec::from_slice(bytes).ok()?,
+    })
+}

tines-core/src/lib.rs

@@ -7,6 +7,9 @@ extern crate alloc;
 
 pub mod belief;
 mod bloom;
+#[cfg(feature = "conformance")]
+#[doc(hidden)]
+pub mod conformance;
 pub mod consts;
 mod exchange;
 mod frag;
@@ -28,10 +31,18 @@ pub use observation::{
 };
 pub use store::{Store, StoreError, TrimPolicy, WallClockStore};
 pub use transport::{Event, FrameBuf, SendError, Transport};
-pub use wire::{frame_sender, Frame, WireError};
+pub use wire::frame_sender;
 
 #[cfg(feature = "alloc")]
 pub use mem_store::MemStore;
 
 #[cfg(test)]
 extern crate std;
+
+// The pinned wire vectors (spec §7) need the crate-private `Frame` and
+// `WireError`, so they compile as a unit-test module rather than as an
+// integration test (`autotests = false` in Cargo.toml keeps Cargo from also
+// building them as one).
+#[cfg(test)]
+#[path = "../tests/vectors.rs"]
+mod vectors;

tines-core/src/wire.rs

@@ -14,13 +14,21 @@ use serde::{Deserialize, Serialize};
 /// avoid per-frame heap allocation in the `no_std` core; this keeps the enum
 /// large, so the informative `large_enum_variant` lint is suppressed here.
 ///
-/// Exposed publicly (see [`crate::Frame`]) so that `tines-core/tests/vectors.rs`
-/// can decode the pinned golden wire vectors and assert on the decoded shape.
-/// The wire layout (version byte, positional postcard tags, reserved Signature
-/// slot) is the frozen contract this crate guarantees across 0.x → 1.0.
+/// Crate-private (spec §3): the type is not API, but its encoding is. The
+/// wire layout (version byte, positional postcard tags, reserved Signature
+/// slot) is frozen for wire v1 and pinned byte-for-byte by
+/// `tines-core/tests/vectors.rs`, which runs as an in-crate test module.
+///
+/// ```compile_fail
+/// use tines_core::Frame; // crate-private: not reachable from outside core
+/// ```
+///
+/// ```compile_fail
+/// use tines_core::WireError; // crate-private too
+/// ```
 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
 #[allow(clippy::large_enum_variant)]
-pub enum Frame {
+pub(crate) enum Frame {
     /// A broadcast bloom summary of a node's observation-id set.
     Summary {
         /// The sending node.
@@ -143,13 +151,10 @@ pub fn frame_sender(bytes: &[u8]) -> Option<NodeId> {
     Some(from)
 }
 
-/// Errors produced while (de)serializing frames on the wire.
-///
-/// Exposed publicly (see [`crate::WireError`]) so that `tines-core/tests/vectors.rs`
-/// can assert on the exact decode error (e.g. `VersionMismatch`) for the pinned
-/// malformed vectors.
+/// Errors produced while (de)serializing frames on the wire. Crate-private
+/// (spec §3); the exchange reports decode failures as [`crate::DropReason`].
 #[derive(Debug, PartialEq, Eq)]
-pub enum WireError {
+pub(crate) enum WireError {
     /// The output buffer was too small to hold the serialized frame.
     TooLarge,
     /// The input bytes were malformed, truncated, or not a valid `Frame`.
@@ -315,7 +320,8 @@ mod tests {
 
     #[test]
     fn frame_sender_peeks_from_field() {
-        // Version byte 0, variant tag 1, then `from: [3;16]` at bytes 2..18.
+        // Version byte (`WIRE_VERSION` = 4) at byte 0, variant tag 0
+        // (Summary) at byte 1, then `from: [3;16]` at bytes 2..18.
         const GOLDEN: [u8; 201] = [
             4u8, 0u8, 3u8, 3u8, 3u8, 3u8, 3u8, 3u8, 3u8, 3u8, 3u8, 3u8, 3u8, 3u8, 3u8, 3u8, 3u8,
             3u8, 239u8, 253u8, 182u8, 245u8, 13u8, 128u8, 4u8, 170u8, 170u8, 170u8, 170u8, 170u8,
@@ -340,9 +346,9 @@ mod tests {
 
     #[test]
     fn frame_sender_reads_from_fixed_offset_not_just_the_start() {
-        // The leading byte (the externally-tagged variant tag) is skipped, so a
-        // payload whose first byte is not the sender must still yield the `from`
-        // recorded at byte 1.
+        // The two leading bytes (the version byte and the externally-tagged
+        // variant tag) are skipped, so a payload whose first bytes are not the
+        // sender must still yield the `from` recorded at bytes 2..18.
         let bytes = {
             let mut b = [0u8; 32];
             b[0] = consts::WIRE_VERSION; // version slot (skipped by frame_sender)
@@ -514,53 +520,4 @@ mod tests {
             other => panic!("expected Obs, got {other:?}"),
         }
     }
-
-    #[test]
-    fn gen_missing_golden_vectors() {
-        // THROWAWAY: encode canonical frames and print hex for vectors.rs.
-        let enc = |f: Frame| {
-            let mut buf = [0u8; consts::MAX_FRAME];
-            let n = f.encode(&mut buf).unwrap();
-            let hex: std::string::String =
-                buf[..n].iter().map(|b| std::format!("{b:02x}")).collect();
-            std::println!("{n} {hex}");
-        };
-
-        // unknown-algo Obs
-        let f = Frame::Obs {
-            from: [1; 16],
-            obs: Observation {
-                observer: [1; 16],
-                seq: 1,
-                age_ms: 0,
-                observed_at: None,
-                topic: Topic::from_slice(b"door/3").unwrap(),
-                payload: Payload::from_slice(&[0u8; consts::MAX_PAYLOAD]).unwrap(),
-                dest: None,
-                sig: Some(Signature {
-                    version: 1,
-                    algo: SigAlgo::Unknown(7),
-                    bytes: Vec::from_slice(&[0u8; 64]).unwrap(),
-                }),
-            },
-        };
-        enc(f);
-
-        // Frag
-        let f = Frame::Frag {
-            from: [1; 16],
-            id: [2; 16],
-            index: 0,
-            count: 1,
-            data: Vec::from_slice(&[0x5Cu8; 64]).unwrap(),
-        };
-        enc(f);
-
-        // Ack
-        let ids =
-            Vec::<ObservationId, { consts::ACK_IDS_CAP }>::from_slice(&[[2u8; 16], [3u8; 16]])
-                .unwrap();
-        let f = Frame::Ack { from: [1; 16], ids };
-        enc(f);
-    }
 }

tines-core/tests/vectors.rs

@@ -1,7 +1,53 @@
 //! Pinned identity + wire vectors (spec §7 "Evidence"). A change to any byte
 //! or expected shape below is an identity- or wire-format change by definition.
+//!
+//! `Frame` and `WireError` are crate-private (spec §3), so this file is not a
+//! Cargo integration-test target: `tines-core/src/lib.rs` compiles it into the
+//! crate's own unit tests with `#[cfg(test)] #[path = "../tests/vectors.rs"]`.
+//! Each golden vector is checked both ways: the hand-built frame must
+//! `encode()` to exactly the pinned bytes, and the pinned bytes must
+//! `decode()` back to that frame.
 
-use tines_core::{consts, Frame, Observation, SigAlgo, WireError};
+use crate::consts;
+use crate::wire::{Frame, WireError};
+use crate::{Dest, Observation, Payload, SigAlgo, Signature, Topic};
+use heapless::Vec;
+
+/// Encodes `frame` and asserts the bytes equal `golden`, then decodes
+/// `golden` and asserts it equals `frame`.
+fn assert_golden(frame: &Frame, golden: &[u8]) {
+    let mut buf = [0u8; consts::MAX_FRAME];
+    let n = frame.encode(&mut buf).expect("golden frame encodes");
+    assert_eq!(
+        &buf[..n],
+        golden,
+        "encode() must reproduce the pinned bytes"
+    );
+    assert_eq!(
+        Frame::decode(golden).as_ref(),
+        Ok(frame),
+        "decode() of the pinned bytes must give the frame"
+    );
+}
+
+/// The `[1;16]` / seq 1 / `"door/3"` / `MAX_PAYLOAD` zero-byte broadcast both
+/// signed vectors carry, signed with 64 zero bytes under `algo`.
+fn signed_door_obs(algo: SigAlgo) -> Observation {
+    Observation {
+        observer: [1; 16],
+        seq: 1,
+        age_ms: 0,
+        observed_at: None,
+        topic: Topic::from_slice(b"door/3").unwrap(),
+        payload: Payload::from_slice(&[0u8; consts::MAX_PAYLOAD]).unwrap(),
+        dest: None,
+        sig: Some(Signature {
+            version: 1,
+            algo,
+            bytes: Vec::from_slice(&[0u8; 64]).unwrap(),
+        }),
+    }
+}
 
 #[test]
 fn id_known_vector() {
@@ -62,12 +108,12 @@ fn summary_golden_vector() {
         170u8, 170u8, 170u8, 170u8, 170u8, 170u8, 170u8, 170u8, 170u8, 170u8, 170u8, 170u8, 170u8,
         170u8, 170u8, 170u8, 170u8, 170u8, 170u8, 170u8, 170u8, 170u8, 170u8, 170u8, 170u8,
     ];
-    let Frame::Summary { from, salt, bits } = Frame::decode(&GOLDEN).unwrap() else {
-        panic!("expected a Summary frame")
+    let frame = Frame::Summary {
+        from: [3; 16],
+        salt: 0xdeadbeef,
+        bits: Vec::from_slice(&[0xAAu8; consts::SUMMARY_BYTES]).unwrap(),
     };
-    assert_eq!(from, [3; 16]);
-    assert_eq!(salt, 0xdeadbeef);
-    assert_eq!(&bits[..], &[0xAAu8; consts::SUMMARY_BYTES][..]);
+    assert_golden(&frame, &GOLDEN);
 }
 
 #[test]
@@ -150,22 +196,11 @@ fn obs_golden_vector_ed25519() {
         0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
         0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
     ];
-    let Frame::Obs { from, obs } = Frame::decode(&GOLDEN).unwrap() else {
-        panic!("expected an Obs frame")
+    let frame = Frame::Obs {
+        from: [1; 16],
+        obs: signed_door_obs(SigAlgo::Ed25519),
     };
-    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));
+    assert_golden(&frame, &GOLDEN);
 }
 
 #[test]
@@ -248,17 +283,11 @@ fn obs_golden_vector_unknown_algo() {
         0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
         0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
     ];
-    let Frame::Obs { obs, .. } = Frame::decode(&GOLDEN).unwrap() else {
-        panic!("expected an Obs frame")
+    let frame = Frame::Obs {
+        from: [1; 16],
+        obs: signed_door_obs(SigAlgo::Unknown(7)),
     };
-    assert_eq!(obs.observer, [1; 16]);
-    assert_eq!(obs.seq, 1);
-    assert_eq!(obs.observed_at, None);
-    let sig = obs.sig.expect("a signed obs carries a signature");
-    assert_eq!(sig.version, 1);
-    assert_eq!(sig.algo, SigAlgo::Unknown(7));
-    assert_eq!(sig.bytes.len(), 64);
-    assert!(sig.bytes.iter().all(|b| *b == 0));
+    assert_golden(&frame, &GOLDEN);
 }
 
 #[test]
@@ -272,21 +301,14 @@ fn frag_golden_vector() {
         0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c,
         0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c, 0x5c,
     ];
-    let Frame::Frag {
-        from,
-        id,
-        index,
-        count,
-        data,
-    } = Frame::decode(&GOLDEN).unwrap()
-    else {
-        panic!("expected a Frag frame")
+    let frame = Frame::Frag {
+        from: [1; 16],
+        id: [2; 16],
+        index: 0,
+        count: 1,
+        data: Vec::from_slice(&[0x5Cu8; 64]).unwrap(),
     };
-    assert_eq!(from, [1; 16]);
-    assert_eq!(id, [2; 16]);
-    assert_eq!(index, 0);
-    assert_eq!(count, 1);
-    assert_eq!(&data[..], &[0x5Cu8; 64][..]);
+    assert_golden(&frame, &GOLDEN);
 }
 
 #[test]
@@ -297,11 +319,55 @@ fn ack_golden_vector() {
         0x02, 0x02, 0x02, 0x02, 0x02, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03,
         0x03, 0x03, 0x03, 0x03, 0x03, 0x03,
     ];
-    let Frame::Ack { from, ids } = Frame::decode(&GOLDEN).unwrap() else {
-        panic!("expected an Ack frame")
+    let frame = Frame::Ack {
+        from: [1; 16],
+        ids: Vec::from_slice(&[[2u8; 16], [3u8; 16]]).unwrap(),
     };
-    assert_eq!(from, [1; 16]);
-    assert_eq!(&ids[..], &[[2u8; 16], [3u8; 16]][..]);
+    assert_golden(&frame, &GOLDEN);
+}
+
+#[test]
+fn ack_with_trailing_byte_is_malformed() {
+    // F13 / §10: frames are canonical. This is the Ack golden vector above
+    // plus one trailing 0x00 byte; the version byte matches and postcard can
+    // decode the Ack, but the leftover byte makes the whole frame Malformed.
+    const TRAILING: [u8; 52] = [
+        0x04, 0x03, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01, 0x01,
+        0x01, 0x01, 0x01, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02, 0x02,
+        0x02, 0x02, 0x02, 0x02, 0x02, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x03,
+        0x03, 0x03, 0x03, 0x03, 0x03, 0x03, 0x00,
+    ];
+    assert_eq!(Frame::decode(&TRAILING), Err(WireError::Malformed));
+}
+
+#[test]
+fn addressed_obs_golden_vector() {
+    // An addressed observation with a nonzero age and an `observed_at`, so
+    // the vectors pin the `Dest` layout and both optional/varint fields.
+    const GOLDEN: [u8; 73] = [
+        0x04, 0x01, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05, 0x05,
+        0x05, 0x05, 0x05, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06, 0x06,
+        0x06, 0x06, 0x06, 0x06, 0xac, 0x02, 0xd2, 0x09, 0x01, 0x80, 0xd0, 0x95, 0xff, 0xbc, 0x31,
+        0x03, 0x63, 0x6d, 0x64, 0x02, 0x67, 0x6f, 0x01, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07,
+        0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0x07, 0xe0, 0xd4, 0x03, 0x00,
+    ];
+    let frame = Frame::Obs {
+        from: [5; 16],
+        obs: Observation {
+            observer: [6; 16],
+            seq: 300,
+            age_ms: 1234,
+            observed_at: Some(1_700_000_000_000),
+            topic: Topic::from_slice(b"cmd").unwrap(),
+            payload: Payload::from_slice(b"go").unwrap(),
+            dest: Some(Dest {
+                to: [7; 16],
+                lifetime_ms: 60_000,
+            }),
+            sig: None,
+        },
+    };
+    assert_golden(&frame, &GOLDEN);
 }
 
 #[test]