Journaling: capture at the queue, the built-in journal, retention

Phase 2 of the journaling spec.

- A copy of each message is taken in MessageWrapper::queue, after DLP and
  transport rules, for every enabled journal that takes it (direction and
  scope: everyone, or accounts, groups, domains, tenants). If the copy
  can't be taken the message isn't queued (temporary failure).
- The journal report: the envelope one field a line (sender, To, Cc, Bcc
  from the envelope, list members from their ORCPT, direction, held for
  review), then the queued message byte for byte as message/rfc822.
- The built-in journal under J in the inbuxa subspace: one chain per node
  whose links name each entry by SHA-256, so entries can expire out of
  chain order; purge leaves a marker, and verify catches an entry changed
  or removed early and a report that doesn't match.
- Retention per journal (30 to 3650 days); an entry keeps what it was
  written with. The daily maintenance purges what's due, keeping entries
  whose people a legal hold covers (deleted accounts a hold keeps too),
  and records the counts in the audit log.
- inbuxa:Journal get/set, audited by the request layer. Permissions
  680-683: administrators see and change journals; the Compliance Officer
  sees, searches and exports. Whoever changes journals may grant search and
  export without holding them, so officers can still be appointed.
- Catalog entries (inbuxa:Journal, source "journal"); spec as-built notes.

tests/src/system/journal.rs: validation, internal mail with a Bcc,
outgoing into two journals, incoming over LMTP, the report and its
original, tamper and early removal caught, hold-aware purge, retention
changes leave entries alone, disabled and removed journals take nothing.

crates/features/src/journal/entries.rs

@@ -0,0 +1,689 @@
+/*
+ * SPDX-FileCopyrightText: 2026 Coffey Labs
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+//! The built-in journal (JR-5, JR-6, JR-13). Keys, after `J`:
+//!
+//! - `e` + node + seq: a chain link: its seq, the hash of the link before
+//!   it, and the SHA-256 of its entry. One chain per node, as the audit log
+//!   keeps (AU-6), but a link names its entry by hash instead of holding it,
+//!   so an entry can go at the end of its own retention without breaking
+//!   the chain: entries don't expire in chain order.
+//! - `c` + node + seq: the entry, as JSON; its bytes are what the link's
+//!   hash names.
+//! - `p` + node + seq: when an entry past its retention was purged. A link
+//!   whose entry is gone without this marker is a broken chain.
+//! - `t` + time + node + seq: the time index, for search.
+//! - `x` + expiry + node + seq: the expiry index, for purge.
+//! - `h` + node: the chain's head: its hash, then its seq as the last eight
+//!   bytes, which each append asserts.
+//! - `f` + node: where the chain starts after purged links at its start
+//!   were cleared, and the hash the first kept link names.
+//!
+//! The report itself is a blob, kept by a temporary link that lasts until
+//! its entry is purged. Nothing here changes or removes an entry before
+//! its time; nothing in JMAP can.
+
+use super::{Direction, FEATURE, Json};
+use crate::hold::HELD_UNTIL;
+use serde::{Deserialize as SerdeDeserialize, Serialize as SerdeSerialize};
+use sha2::{Digest, Sha256};
+use std::fmt;
+use store::{
+    BlobStore, Deserialize, IterateParams, SUBSPACE_INBUXA, Serialize, Store, ValueKey,
+    write::{AnyClass, BatchBuilder, BlobLink, BlobOp, ValueClass, assert::AssertValue},
+};
+use tokio::sync::Mutex;
+use trc::AddContext;
+use types::blob_hash::BlobHash;
+
+const KIND_LINK: u8 = b'e';
+const KIND_CONTENT: u8 = b'c';
+const KIND_PURGED: u8 = b'p';
+const KIND_TIME: u8 = b't';
+const KIND_EXPIRY: u8 = b'x';
+const KIND_HEAD: u8 = b'h';
+const KIND_FLOOR: u8 = b'f';
+
+const APPEND_ATTEMPTS: usize = 5;
+/// Entries purged per batch.
+const PURGE_BATCH: usize = 100;
+
+/// Where one entry sits: its node's chain and its place in it.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
+pub struct EntryId {
+    pub node: u64,
+    pub seq: u64,
+}
+
+impl EntryId {
+    /// As one number, for JMAP ids: the node in the top 16 bits.
+    pub fn to_u64(&self) -> u64 {
+        (self.node << 48) | (self.seq & ((1 << 48) - 1))
+    }
+
+    pub fn from_u64(id: u64) -> Self {
+        EntryId {
+            node: id >> 48,
+            seq: id & ((1 << 48) - 1),
+        }
+    }
+}
+
+impl fmt::Display for EntryId {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}-{}", self.node, self.seq)
+    }
+}
+
+/// One journaled message (JR-5).
+#[derive(Debug, Clone, PartialEq, Eq, SerdeSerialize, SerdeDeserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct Entry {
+    pub queue_id: u64,
+    /// Seconds.
+    pub at: u64,
+    pub direction: Direction,
+    pub sender: String,
+    pub authenticated: bool,
+    pub recipients: Vec<String>,
+    pub subject: String,
+    pub message_id: String,
+    /// The people here on either side, whose holds keep the entry.
+    pub accounts: Vec<u32>,
+    pub tenants: Vec<u32>,
+    /// The journals that took it.
+    pub journals: Vec<u32>,
+    pub held: bool,
+    /// The report's blob, hex.
+    pub blob: String,
+    pub size: u64,
+    /// SHA-256 of the report, hex.
+    pub sha256: String,
+    /// Seconds.
+    pub expires_at: u64,
+}
+
+impl Entry {
+    pub fn blob_hash(&self) -> Option<BlobHash> {
+        let bytes = unhex(&self.blob)?;
+        BlobHash::try_from_hash_slice(&bytes).ok()
+    }
+}
+
+#[derive(Debug, Clone, SerdeSerialize, SerdeDeserialize)]
+#[serde(rename_all = "camelCase")]
+struct Link {
+    seq: u64,
+    prev: String,
+    content: String,
+}
+
+#[derive(Debug, Clone, Default, PartialEq, SerdeSerialize, SerdeDeserialize)]
+struct Floor {
+    seq: u64,
+    prev: String,
+}
+
+#[derive(Debug, Clone, Default, PartialEq)]
+struct Head {
+    seq: u64,
+    hash: String,
+}
+
+impl Head {
+    fn to_bytes(&self) -> Vec<u8> {
+        let mut bytes = self.hash.as_bytes().to_vec();
+        bytes.extend_from_slice(&self.seq.to_be_bytes());
+        bytes
+    }
+}
+
+impl Deserialize for Head {
+    fn deserialize(bytes: &[u8]) -> trc::Result<Self> {
+        let split = bytes.len().checked_sub(8).ok_or_else(|| {
+            trc::StoreEvent::DataCorruption
+                .into_err()
+                .details("Invalid journal chain head")
+        })?;
+        Ok(Head {
+            seq: u64::from_be_bytes(bytes[split..].try_into().unwrap()),
+            hash: String::from_utf8_lossy(&bytes[..split]).into_owned(),
+        })
+    }
+}
+
+struct Raw(Vec<u8>);
+
+impl Deserialize for Raw {
+    fn deserialize(bytes: &[u8]) -> trc::Result<Self> {
+        Ok(Raw(bytes.to_vec()))
+    }
+}
+
+fn class(kind: u8, parts: &[u64]) -> ValueClass {
+    let mut key = Vec::with_capacity(2 + parts.len() * 8);
+    key.push(FEATURE);
+    key.push(kind);
+    for part in parts {
+        key.extend_from_slice(&part.to_be_bytes());
+    }
+    ValueClass::Any(AnyClass {
+        subspace: SUBSPACE_INBUXA,
+        key,
+    })
+}
+
+fn key(kind: u8, parts: &[u64]) -> ValueKey<ValueClass> {
+    ValueKey::from(class(kind, parts))
+}
+
+/// Where an entry's content is kept, for tests that check tampering shows.
+pub fn content_key(id: EntryId) -> ValueKey<ValueClass> {
+    key(KIND_CONTENT, &[id.node, id.seq])
+}
+
+/// The numbers after the kind byte, from the key's tail.
+fn parse_key(key: &[u8], kind: u8, parts: usize) -> Option<Vec<u64>> {
+    let len = 2 + parts * 8;
+    let tail = key.get(key.len().checked_sub(len)?..)?;
+    (tail[0] == FEATURE && tail[1] == kind).then_some(())?;
+    Some(
+        tail[2..]
+            .chunks_exact(8)
+            .map(|chunk| u64::from_be_bytes(chunk.try_into().unwrap()))
+            .collect(),
+    )
+}
+
+pub fn hex(bytes: &[u8]) -> String {
+    bytes.iter().map(|b| format!("{b:02x}")).collect()
+}
+
+fn unhex(value: &str) -> Option<Vec<u8>> {
+    (value.len() % 2 == 0).then_some(())?;
+    (0..value.len())
+        .step_by(2)
+        .map(|i| u8::from_str_radix(value.get(i..i + 2)?, 16).ok())
+        .collect()
+}
+
+pub fn sha256(bytes: &[u8]) -> String {
+    hex(&Sha256::digest(bytes))
+}
+
+async fn head(data: &Store, node: u64) -> trc::Result<Option<Head>> {
+    data.get_value::<Head>(key(KIND_HEAD, &[node]))
+        .await
+        .caused_by(trc::location!())
+}
+
+async fn floor(data: &Store, node: u64) -> trc::Result<Floor> {
+    Ok(data
+        .get_value::<Json<Floor>>(key(KIND_FLOOR, &[node]))
+        .await
+        .caused_by(trc::location!())?
+        .map(|Json(floor)| floor)
+        .unwrap_or(Floor {
+            seq: 1,
+            prev: String::new(),
+        }))
+}
+
+async fn nodes(data: &Store) -> trc::Result<Vec<u64>> {
+    let mut nodes = Vec::new();
+    data.iterate(
+        IterateParams::new(key(KIND_HEAD, &[0]), key(KIND_HEAD, &[u64::MAX])).no_values(),
+        |key, _| {
+            if let Some(parts) = parse_key(key, KIND_HEAD, 1) {
+                nodes.push(parts[0]);
+            }
+            Ok(true)
+        },
+    )
+    .await
+    .caused_by(trc::location!())?;
+    Ok(nodes)
+}
+
+/// Lines up this process's appends; the store's assert settles the rest.
+static APPENDING: Mutex<()> = Mutex::const_new(());
+
+/// Adds an entry to this node's chain, and links its report's blob (already
+/// written) until the entry is purged. An error means nothing was written.
+pub async fn append(data: &Store, node: u64, entry: &Entry) -> trc::Result<EntryId> {
+    let blob = entry.blob_hash().ok_or_else(|| {
+        trc::StoreEvent::UnexpectedError
+            .into_err()
+            .details("Journal entry without a blob")
+    })?;
+    let content = Json(entry).serialize()?;
+    let content_hash = sha256(&content);
+    let _appending = APPENDING.lock().await;
+    let mut attempt = 0;
+    loop {
+        attempt += 1;
+        let current = head(data, node).await?;
+        let (seq, prev) = current
+            .as_ref()
+            .map_or((1, String::new()), |head| (head.seq + 1, head.hash.clone()));
+        let link = Json(&Link {
+            seq,
+            prev,
+            content: content_hash.clone(),
+        })
+        .serialize()?;
+        let new_head = Head {
+            seq,
+            hash: sha256(&link),
+        };
+
+        let mut batch = BatchBuilder::new();
+        batch.assert_value(
+            class(KIND_HEAD, &[node]),
+            current.map_or(AssertValue::None, |head| AssertValue::U64(head.seq)),
+        );
+        batch
+            .set(class(KIND_LINK, &[node, seq]), link)
+            .set(class(KIND_CONTENT, &[node, seq]), content.clone())
+            .set(class(KIND_TIME, &[entry.at, node, seq]), vec![])
+            .set(class(KIND_EXPIRY, &[entry.expires_at, node, seq]), vec![])
+            .set(class(KIND_HEAD, &[node]), new_head.to_bytes())
+            .set(
+                BlobOp::Link {
+                    hash: blob.clone(),
+                    to: BlobLink::Temporary { until: HELD_UNTIL },
+                },
+                vec![],
+            )
+            .set(BlobOp::Commit { hash: blob.clone() }, vec![]);
+        match data.write(batch.build_all()).await {
+            Ok(_) => return Ok(EntryId { node, seq }),
+            Err(err)
+                if attempt < APPEND_ATTEMPTS
+                    && matches!(
+                        err.as_ref(),
+                        trc::EventType::Store(trc::StoreEvent::AssertValueFailed)
+                    ) => {}
+            Err(err) => return Err(err.caused_by(trc::location!())),
+        }
+    }
+}
+
+/// One entry, unless it was purged.
+pub async fn get(data: &Store, id: EntryId) -> trc::Result<Option<Entry>> {
+    Ok(data
+        .get_value::<Json<Entry>>(key(KIND_CONTENT, &[id.node, id.seq]))
+        .await
+        .caused_by(trc::location!())?
+        .map(|Json(entry)| entry))
+}
+
+/// Entries written in `[after, before)` (seconds), newest first, up to
+/// `limit`.
+pub async fn list(
+    data: &Store,
+    after: u64,
+    before: u64,
+    limit: usize,
+) -> trc::Result<Vec<(EntryId, Entry)>> {
+    let mut ids = Vec::new();
+    data.iterate(
+        IterateParams::new(
+            key(KIND_TIME, &[after, 0, 0]),
+            key(KIND_TIME, &[before.saturating_sub(1), u64::MAX, u64::MAX]),
+        )
+        .descending()
+        .no_values(),
+        |key, _| {
+            if let Some(parts) = parse_key(key, KIND_TIME, 3) {
+                ids.push(EntryId {
+                    node: parts[1],
+                    seq: parts[2],
+                });
+            }
+            Ok(ids.len() < limit)
+        },
+    )
+    .await
+    .caused_by(trc::location!())?;
+    let mut out = Vec::with_capacity(ids.len());
+    for id in ids {
+        if let Some(entry) = get(data, id).await? {
+            out.push((id, entry));
+        }
+    }
+    Ok(out)
+}
+
+/// What a purge did.
+#[derive(Debug, Clone, Default, PartialEq, Eq)]
+pub struct Purged {
+    pub removed: usize,
+    /// Past their time, kept for a legal hold.
+    pub kept_for_hold: usize,
+}
+
+/// Removes entries past their retention (JR-13), except those `held` keeps:
+/// the entry, its indexes and its blob's link go; the chain link stays,
+/// with a purge marker. Then each chain's start moves past purged links.
+pub async fn purge(
+    data: &Store,
+    now: u64,
+    held: impl Fn(&Entry) -> bool + Sync + Send,
+) -> trc::Result<Purged> {
+    let mut due = Vec::new();
+    data.iterate(
+        IterateParams::new(
+            key(KIND_EXPIRY, &[0, 0, 0]),
+            key(KIND_EXPIRY, &[now, u64::MAX, u64::MAX]),
+        )
+        .ascending()
+        .no_values(),
+        |key, _| {
+            if let Some(parts) = parse_key(key, KIND_EXPIRY, 3) {
+                due.push((
+                    parts[0],
+                    EntryId {
+                        node: parts[1],
+                        seq: parts[2],
+                    },
+                ));
+            }
+            Ok(due.len() < 100_000)
+        },
+    )
+    .await
+    .caused_by(trc::location!())?;
+
+    let mut purged = Purged::default();
+    for chunk in due.chunks(PURGE_BATCH) {
+        let mut batch = BatchBuilder::new();
+        for (expires_at, id) in chunk {
+            let parts = [id.node, id.seq];
+            let Some(entry) = get(data, *id).await? else {
+                // Its entry is already gone: only the index is left
+                batch.clear(class(KIND_EXPIRY, &[*expires_at, id.node, id.seq]));
+                continue;
+            };
+            if held(&entry) {
+                purged.kept_for_hold += 1;
+                continue;
+            }
+            batch
+                .clear(class(KIND_CONTENT, &parts))
+                .clear(class(KIND_TIME, &[entry.at, id.node, id.seq]))
+                .clear(class(KIND_EXPIRY, &[*expires_at, id.node, id.seq]))
+                .set(class(KIND_PURGED, &parts), now.to_be_bytes().to_vec());
+            if let Some(blob) = entry.blob_hash() {
+                batch.clear(BlobOp::Link {
+                    hash: blob,
+                    to: BlobLink::Temporary { until: HELD_UNTIL },
+                });
+            }
+            purged.removed += 1;
+        }
+        if !batch.is_empty() {
+            data.write(batch.build_all())
+                .await
+                .caused_by(trc::location!())?;
+        }
+    }
+
+    for node in nodes(data).await? {
+        advance_floor(data, node).await?;
+    }
+    Ok(purged)
+}
+
+/// Clears the purged links at the start of a node's chain, recording where
+/// it now starts and the hash that start names.
+async fn advance_floor(data: &Store, node: u64) -> trc::Result<()> {
+    let start = floor(data, node).await?;
+    let mut cleared: Vec<u64> = Vec::new();
+    let mut next = start.clone();
+    let mut purged_seqs = Vec::new();
+    data.iterate(
+        IterateParams::new(
+            key(KIND_PURGED, &[node, start.seq]),
+            key(KIND_PURGED, &[node, u64::MAX]),
+        )
+        .ascending()
+        .no_values(),
+        |key, _| {
+            if let Some(parts) = parse_key(key, KIND_PURGED, 2) {
+                purged_seqs.push(parts[1]);
+            }
+            Ok(purged_seqs.len() < 100_000)
+        },
+    )
+    .await
+    .caused_by(trc::location!())?;
+    for seq in purged_seqs {
+        if seq != next.seq {
+            break;
+        }
+        let Some(Raw(link)) = data
+            .get_value::<Raw>(key(KIND_LINK, &[node, seq]))
+            .await
+            .caused_by(trc::location!())?
+        else {
+            break;
+        };
+        next = Floor {
+            seq: seq + 1,
+            prev: sha256(&link),
+        };
+        cleared.push(seq);
+    }
+    if cleared.is_empty() {
+        return Ok(());
+    }
+    // The floor moves first: a run cut short leaves links before it, which
+    // the next run clears, never a chain that looks broken
+    let mut batch = BatchBuilder::new();
+    batch.set(class(KIND_FLOOR, &[node]), Json(&next).serialize()?);
+    data.write(batch.build_all())
+        .await
+        .caused_by(trc::location!())?;
+    for chunk in cleared.chunks(PURGE_BATCH) {
+        let mut batch = BatchBuilder::new();
+        for seq in chunk {
+            batch
+                .clear(class(KIND_LINK, &[node, *seq]))
+                .clear(class(KIND_PURGED, &[node, *seq]));
+        }
+        data.write(batch.build_all())
+            .await
+            .caused_by(trc::location!())?;
+    }
+    Ok(())
+}
+
+/// One node's chain, as [`verify`] found it.
+#[derive(Debug, Clone, PartialEq, Eq, SerdeSerialize)]
+#[serde(rename_all = "camelCase")]
+pub struct ChainReport {
+    pub node: u64,
+    pub entries: u64,
+    pub purged: u64,
+    pub first_seq: u64,
+    pub last_seq: u64,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub broken_at: Option<String>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub reason: Option<String>,
+}
+
+/// Rechecks every node's chain (JR-6): each link names the hash of the one
+/// before it, seqs run without gaps, the head matches the last link, each
+/// entry hashes to what its link names or was purged, and, with `blobs`,
+/// each report is there and hashes to what its entry names.
+pub async fn verify(data: &Store, blobs: Option<&BlobStore>) -> trc::Result<Vec<ChainReport>> {
+    let mut reports = Vec::new();
+    for node in nodes(data).await? {
+        let start = floor(data, node).await?;
+        let head = head(data, node).await?.unwrap_or_default();
+        let mut report = ChainReport {
+            node,
+            entries: 0,
+            purged: 0,
+            first_seq: start.seq,
+            last_seq: start.seq.saturating_sub(1),
+            broken_at: None,
+            reason: None,
+        };
+        let mut links = Vec::new();
+        data.iterate(
+            IterateParams::new(
+                key(KIND_LINK, &[node, start.seq]),
+                key(KIND_LINK, &[node, u64::MAX]),
+            )
+            .ascending(),
+            |key, value| {
+                if let Some(parts) = parse_key(key, KIND_LINK, 2) {
+                    links.push((parts[1], value.to_vec()));
+                }
+                Ok(true)
+            },
+        )
+        .await
+        .caused_by(trc::location!())?;
+
+        let mut expected_seq = start.seq;
+        let mut expected_prev = start.prev.clone();
+        for (seq, bytes) in links {
+            let broken = |report: &mut ChainReport, reason: &str| {
+                report.broken_at = Some(EntryId { node, seq }.to_string());
+                report.reason = Some(reason.to_string());
+            };
+            let Ok(Json(link)) = Json::<Link>::deserialize(&bytes) else {
+                broken(&mut report, "The link can't be read.");
+                break;
+            };
+            if seq != expected_seq || link.seq != seq {
+                report.broken_at = Some(EntryId { node, seq }.to_string());
+                report.reason = Some(format!(
+                    "Entry {expected_seq} is missing; the next one found is {seq}."
+                ));
+                break;
+            }
+            if link.prev != expected_prev {
+                broken(
+                    &mut report,
+                    "The link doesn't follow from the one before it: one of them was changed.",
+                );
+                break;
+            }
+            match data
+                .get_value::<Raw>(key(KIND_CONTENT, &[node, seq]))
+                .await
+                .caused_by(trc::location!())?
+            {
+                Some(Raw(content)) => {
+                    if sha256(&content) != link.content {
+                        broken(&mut report, "The entry was changed after it was written.");
+                        break;
+                    }
+                    if let Some(blobs) = blobs {
+                        let Ok(Json(entry)) = Json::<Entry>::deserialize(&content) else {
+                            broken(&mut report, "The entry can't be read.");
+                            break;
+                        };
+                        let report_bytes = match entry.blob_hash() {
+                            Some(hash) => blobs
+                                .get_blob(hash.as_slice(), 0..usize::MAX)
+                                .await
+                                .caused_by(trc::location!())?,
+                            None => None,
+                        };
+                        match report_bytes {
+                            Some(bytes) if sha256(&bytes) == entry.sha256 => {}
+                            Some(_) => {
+                                broken(&mut report, "The report doesn't match its entry.");
+                                break;
+                            }
+                            None => {
+                                broken(&mut report, "The report is missing.");
+                                break;
+                            }
+                        }
+                    }
+                    report.entries += 1;
+                }
+                None => {
+                    if data
+                        .get_value::<Raw>(key(KIND_PURGED, &[node, seq]))
+                        .await
+                        .caused_by(trc::location!())?
+                        .is_none()
+                    {
+                        broken(&mut report, "The entry was removed before its time.");
+                        break;
+                    }
+                    report.purged += 1;
+                }
+            }
+            expected_prev = sha256(&bytes);
+            expected_seq = seq + 1;
+            report.last_seq = seq;
+        }
+
+        if report.broken_at.is_none()
+            && (head.seq != report.last_seq
+                || (report.last_seq >= report.first_seq && head.hash != expected_prev))
+        {
+            report.broken_at = Some(
+                EntryId {
+                    node,
+                    seq: report.last_seq,
+                }
+                .to_string(),
+            );
+            report.reason = Some(
+                "The chain's recorded end doesn't match its last link: entries were removed \
+                 or changed at the end."
+                    .into(),
+            );
+        }
+        reports.push(report);
+    }
+    Ok(reports)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn keys_read_back() {
+        let ValueClass::Any(any) = class(KIND_EXPIRY, &[5, 3, 9]) else {
+            panic!()
+        };
+        assert_eq!(parse_key(&any.key, KIND_EXPIRY, 3), Some(vec![5, 3, 9]));
+        let mut with_subspace = vec![SUBSPACE_INBUXA];
+        with_subspace.extend_from_slice(&any.key);
+        assert_eq!(
+            parse_key(&with_subspace, KIND_EXPIRY, 3),
+            Some(vec![5, 3, 9])
+        );
+        assert_eq!(parse_key(&any.key, KIND_TIME, 3), None);
+    }
+
+    #[test]
+    fn hex_round_trips() {
+        let bytes = [0u8, 1, 0xab, 0xff];
+        assert_eq!(unhex(&hex(&bytes)), Some(bytes.to_vec()));
+        assert_eq!(unhex("abc"), None);
+        assert_eq!(unhex("zz"), None);
+    }
+
+    #[test]
+    fn ids_read_back() {
+        let id = EntryId { node: 3, seq: 77 };
+        assert_eq!(EntryId::from_u64(id.to_u64()), id);
+        assert_eq!(id.to_string(), "3-77");
+    }
+}