feat: rework record sync for improved reliability (#1478)

* feat: rework record sync for improved reliability

So, to tell a story

1. We introduced the record sync, intended to be the new algorithm to
   sync history.
2. On top of this, I added the KV store. This was intended as a simple
   test of the record sync, and to see if people wanted that sort of
   functionality
3. History remained syncing via the old means, as while it had issues it
   worked more-or-less OK. And we are aware of its flaws
4. If KV syncing worked ok, history would be moved across

KV syncing ran ok for 6mo or so, so I started to move across history.
For several weeks, I ran a local fork of Atuin + the server that synced
via records instead.

The record store maintained ordering via a linked list, which was a
mistake. It performed well in testing, but was really difficult to debug
and reason about. So when a few small sync issues occured, they took an
extremely long time to debug.

This PR is huge, which I regret. It involves replacing the "parent"
relationship that records once had (pointing to the previous record)
with a simple index (generally referred to as idx). This also means we
had to change the recordindex, which referenced "tails". Tails were the
last item in the chain.

Now that we use an "array" vs linked list, that logic was also replaced.
And is much simpler :D

Same for the queries that act on this data.

----

This isn't final - we still need to add

1. Proper server/client error handling, which has been lacking for a
   while
2. The actual history implementation on top
    This exists in a branch, just without deletions. Won't be much to
    add that, I just don't want to make this any larger than it already
    is

The _only_ caveat here is that we basically lose data synced via the old
record store. This is the KV data from before.

It hasn't been deleted or anything, just no longer hooked up. So it's
totally possible to write a migration script. I just need to do that.

* update .gitignore

* use correct endpoint

* fix for stores with length of 1

* use create/delete enum for history store

* lint, remove unneeded host_id

* remove prints

* add command to import old history

* add enable/disable switch for record sync

* add record sync to auto sync

* satisfy the almighty clippy

* remove file that I did not mean to commit

* feedback

9 files changed, 1002 insertions, 397 deletions

diff --git a/atuin-client/src/api_client.rs b/atuin-client/src/api_client.rs
index ae8df5ad..9007b9ab 100644
--- a/atuin-client/src/api_client.rs
+++ b/atuin-client/src/api_client.rs
@@ -13,11 +13,11 @@ use atuin_common::{
         AddHistoryRequest, CountResponse, DeleteHistoryRequest, ErrorResponse, IndexResponse,
         LoginRequest, LoginResponse, RegisterResponse, StatusResponse, SyncHistoryResponse,
     },
-    record::RecordIndex,
+    record::RecordStatus,
 };
 use atuin_common::{
     api::{ATUIN_CARGO_VERSION, ATUIN_HEADER_VERSION, ATUIN_VERSION},
-    record::{EncryptedData, HostId, Record, RecordId},
+    record::{EncryptedData, HostId, Record, RecordIdx},
 };
 use semver::Version;
 use time::format_description::well_known::Rfc3339;
@@ -267,10 +267,18 @@ impl<'a> Client<'a> {
     }
 
     pub async fn post_records(&self, records: &[Record<EncryptedData>]) -> Result<()> {
-        let url = format!("{}/record", self.sync_addr);
+        let url = format!("{}/api/v0/record", self.sync_addr);
         let url = Url::parse(url.as_str())?;
 
-        self.client.post(url).json(records).send().await?;
+        let resp = self.client.post(url).json(records).send().await?;
+        info!("posted records, got {}", resp.status());
+
+        if !resp.status().is_success() {
+            error!(
+                "failed to post records to server; got: {:?}",
+                resp.text().await
+            );
+        }
 
         Ok(())
     }
@@ -279,24 +287,22 @@ impl<'a> Client<'a> {
         &self,
         host: HostId,
         tag: String,
-        start: Option<RecordId>,
+        start: RecordIdx,
         count: u64,
     ) -> Result<Vec<Record<EncryptedData>>> {
+        debug!(
+            "fetching record/s from host {}/{}/{}",
+            host.0.to_string(),
+            tag,
+            start
+        );
+
         let url = format!(
-            "{}/record/next?host={}&tag={}&count={}",
-            self.sync_addr, host.0, tag, count
+            "{}/api/v0/record/next?host={}&tag={}&count={}&start={}",
+            self.sync_addr, host.0, tag, count, start
         );
-        let mut url = Url::parse(url.as_str())?;
-
-        if let Some(start) = start {
-            url.set_query(Some(
-                format!(
-                    "host={}&tag={}&count={}&start={}",
-                    host.0, tag, count, start.0
-                )
-                .as_str(),
-            ));
-        }
+
+        let url = Url::parse(url.as_str())?;
 
         let resp = self.client.get(url).send().await?;
 
@@ -305,8 +311,8 @@ impl<'a> Client<'a> {
         Ok(records)
     }
 
-    pub async fn record_index(&self) -> Result<RecordIndex> {
-        let url = format!("{}/record", self.sync_addr);
+    pub async fn record_status(&self) -> Result<RecordStatus> {
+        let url = format!("{}/api/v0/record", self.sync_addr);
         let url = Url::parse(url.as_str())?;
 
         let resp = self.client.get(url).send().await?;
@@ -317,6 +323,8 @@ impl<'a> Client<'a> {
 
         let index = resp.json().await?;
 
+        debug!("got remote index {:?}", index);
+
         Ok(index)
     }
 
diff --git a/atuin-client/src/history.rs b/atuin-client/src/history.rs
index fbcb169c..2b2c41ee 100644
--- a/atuin-client/src/history.rs
+++ b/atuin-client/src/history.rs
@@ -1,12 +1,21 @@
+use rmp::decode::ValueReadError;
+use rmp::{decode::Bytes, Marker};
 use std::env;
 
+use atuin_common::record::DecryptedData;
 use atuin_common::utils::uuid_v7;
+
+use eyre::{bail, eyre, Result};
 use regex::RegexSet;
 
 use crate::{secrets::SECRET_PATTERNS, settings::Settings};
 use time::OffsetDateTime;
 
 mod builder;
+pub mod store;
+
+const HISTORY_VERSION: &str = "v0";
+const HISTORY_TAG: &str = "history";
 
 /// Client-side history entry.
 ///
@@ -81,6 +90,108 @@ impl History {
         }
     }
 
+    pub fn serialize(&self) -> Result<DecryptedData> {
+        // This is pretty much the same as what we used for the old history, with one difference -
+        // it uses integers for timestamps rather than a string format.
+
+        use rmp::encode;
+
+        let mut output = vec![];
+
+        // write the version
+        encode::write_u16(&mut output, 0)?;
+        // INFO: ensure this is updated when adding new fields
+        encode::write_array_len(&mut output, 9)?;
+
+        encode::write_str(&mut output, &self.id)?;
+        encode::write_u64(&mut output, self.timestamp.unix_timestamp_nanos() as u64)?;
+        encode::write_sint(&mut output, self.duration)?;
+        encode::write_sint(&mut output, self.exit)?;
+        encode::write_str(&mut output, &self.command)?;
+        encode::write_str(&mut output, &self.cwd)?;
+        encode::write_str(&mut output, &self.session)?;
+        encode::write_str(&mut output, &self.hostname)?;
+
+        match self.deleted_at {
+            Some(d) => encode::write_u64(&mut output, d.unix_timestamp_nanos() as u64)?,
+            None => encode::write_nil(&mut output)?,
+        }
+
+        Ok(DecryptedData(output))
+    }
+
+    fn deserialize_v0(bytes: &[u8]) -> Result<History> {
+        use rmp::decode;
+
+        fn error_report<E: std::fmt::Debug>(err: E) -> eyre::Report {
+            eyre!("{err:?}")
+        }
+
+        let mut bytes = Bytes::new(bytes);
+
+        let version = decode::read_u16(&mut bytes).map_err(error_report)?;
+
+        if version != 0 {
+            bail!("expected decoding v0 record, found v{version}");
+        }
+
+        let nfields = decode::read_array_len(&mut bytes).map_err(error_report)?;
+
+        if nfields != 9 {
+            bail!("cannot decrypt history from a different version of Atuin");
+        }
+
+        let bytes = bytes.remaining_slice();
+        let (id, bytes) = decode::read_str_from_slice(bytes).map_err(error_report)?;
+
+        let mut bytes = Bytes::new(bytes);
+        let timestamp = decode::read_u64(&mut bytes).map_err(error_report)?;
+        let duration = decode::read_int(&mut bytes).map_err(error_report)?;
+        let exit = decode::read_int(&mut bytes).map_err(error_report)?;
+
+        let bytes = bytes.remaining_slice();
+        let (command, bytes) = decode::read_str_from_slice(bytes).map_err(error_report)?;
+        let (cwd, bytes) = decode::read_str_from_slice(bytes).map_err(error_report)?;
+        let (session, bytes) = decode::read_str_from_slice(bytes).map_err(error_report)?;
+        let (hostname, bytes) = decode::read_str_from_slice(bytes).map_err(error_report)?;
+
+        // if we have more fields, try and get the deleted_at
+        let mut bytes = Bytes::new(bytes);
+
+        let (deleted_at, bytes) = match decode::read_u64(&mut bytes) {
+            Ok(unix) => (Some(unix), bytes.remaining_slice()),
+            // we accept null here
+            Err(ValueReadError::TypeMismatch(Marker::Null)) => (None, bytes.remaining_slice()),
+            Err(err) => return Err(error_report(err)),
+        };
+
+        if !bytes.is_empty() {
+            bail!("trailing bytes in encoded history. malformed")
+        }
+
+        Ok(History {
+            id: id.to_owned(),
+            timestamp: OffsetDateTime::from_unix_timestamp_nanos(timestamp as i128)?,
+            duration,
+            exit,
+            command: command.to_owned(),
+            cwd: cwd.to_owned(),
+            session: session.to_owned(),
+            hostname: hostname.to_owned(),
+            deleted_at: deleted_at
+                .map(|t| OffsetDateTime::from_unix_timestamp_nanos(t as i128))
+                .transpose()?,
+        })
+    }
+
+    pub fn deserialize(bytes: &[u8], version: &str) -> Result<History> {
+        match version {
+            HISTORY_VERSION => Self::deserialize_v0(bytes),
+
+            _ => bail!("unknown version {version:?}"),
+        }
+    }
+
     /// Builder for a history entry that is imported from shell history.
     ///
     /// The only two required fields are `timestamp` and `command`.
@@ -202,8 +313,9 @@ impl History {
 #[cfg(test)]
 mod tests {
     use regex::RegexSet;
+    use time::macros::datetime;
 
-    use crate::settings::Settings;
+    use crate::{history::HISTORY_VERSION, settings::Settings};
 
     use super::History;
 
@@ -274,4 +386,100 @@ mod tests {
 
         assert!(stripe_key.should_save(&settings));
     }
+
+    #[test]
+    fn test_serialize_deserialize() {
+        let bytes = [
+            205, 0, 0, 153, 217, 32, 54, 54, 100, 49, 54, 99, 98, 101, 101, 55, 99, 100, 52, 55,
+            53, 51, 56, 101, 53, 99, 53, 98, 56, 98, 52, 52, 101, 57, 48, 48, 54, 101, 207, 23, 99,
+            98, 117, 24, 210, 246, 128, 206, 2, 238, 210, 240, 0, 170, 103, 105, 116, 32, 115, 116,
+            97, 116, 117, 115, 217, 42, 47, 85, 115, 101, 114, 115, 47, 99, 111, 110, 114, 97, 100,
+            46, 108, 117, 100, 103, 97, 116, 101, 47, 68, 111, 99, 117, 109, 101, 110, 116, 115,
+            47, 99, 111, 100, 101, 47, 97, 116, 117, 105, 110, 217, 32, 98, 57, 55, 100, 57, 97,
+            51, 48, 54, 102, 50, 55, 52, 52, 55, 51, 97, 50, 48, 51, 100, 50, 101, 98, 97, 52, 49,
+            102, 57, 52, 53, 55, 187, 102, 118, 102, 103, 57, 51, 54, 99, 48, 107, 112, 102, 58,
+            99, 111, 110, 114, 97, 100, 46, 108, 117, 100, 103, 97, 116, 101, 192,
+        ];
+
+        let history = History {
+            id: "66d16cbee7cd47538e5c5b8b44e9006e".to_owned(),
+            timestamp: datetime!(2023-05-28 18:35:40.633872 +00:00),
+            duration: 49206000,
+            exit: 0,
+            command: "git status".to_owned(),
+            cwd: "/Users/conrad.ludgate/Documents/code/atuin".to_owned(),
+            session: "b97d9a306f274473a203d2eba41f9457".to_owned(),
+            hostname: "fvfg936c0kpf:conrad.ludgate".to_owned(),
+            deleted_at: None,
+        };
+
+        let serialized = history.serialize().expect("failed to serialize history");
+        assert_eq!(serialized.0, bytes);
+
+        let deserialized = History::deserialize(&serialized.0, HISTORY_VERSION)
+            .expect("failed to deserialize history");
+        assert_eq!(history, deserialized);
+
+        // test the snapshot too
+        let deserialized =
+            History::deserialize(&bytes, HISTORY_VERSION).expect("failed to deserialize history");
+        assert_eq!(history, deserialized);
+    }
+
+    #[test]
+    fn test_serialize_deserialize_deleted() {
+        let history = History {
+            id: "66d16cbee7cd47538e5c5b8b44e9006e".to_owned(),
+            timestamp: datetime!(2023-05-28 18:35:40.633872 +00:00),
+            duration: 49206000,
+            exit: 0,
+            command: "git status".to_owned(),
+            cwd: "/Users/conrad.ludgate/Documents/code/atuin".to_owned(),
+            session: "b97d9a306f274473a203d2eba41f9457".to_owned(),
+            hostname: "fvfg936c0kpf:conrad.ludgate".to_owned(),
+            deleted_at: Some(datetime!(2023-11-19 20:18 +00:00)),
+        };
+
+        let serialized = history.serialize().expect("failed to serialize history");
+
+        let deserialized = History::deserialize(&serialized.0, HISTORY_VERSION)
+            .expect("failed to deserialize history");
+
+        assert_eq!(history, deserialized);
+    }
+
+    #[test]
+    fn test_serialize_deserialize_version() {
+        // v0
+        let bytes_v0 = [
+            205, 0, 0, 153, 217, 32, 54, 54, 100, 49, 54, 99, 98, 101, 101, 55, 99, 100, 52, 55,
+            53, 51, 56, 101, 53, 99, 53, 98, 56, 98, 52, 52, 101, 57, 48, 48, 54, 101, 207, 23, 99,
+            98, 117, 24, 210, 246, 128, 206, 2, 238, 210, 240, 0, 170, 103, 105, 116, 32, 115, 116,
+            97, 116, 117, 115, 217, 42, 47, 85, 115, 101, 114, 115, 47, 99, 111, 110, 114, 97, 100,
+            46, 108, 117, 100, 103, 97, 116, 101, 47, 68, 111, 99, 117, 109, 101, 110, 116, 115,
+            47, 99, 111, 100, 101, 47, 97, 116, 117, 105, 110, 217, 32, 98, 57, 55, 100, 57, 97,
+            51, 48, 54, 102, 50, 55, 52, 52, 55, 51, 97, 50, 48, 51, 100, 50, 101, 98, 97, 52, 49,
+            102, 57, 52, 53, 55, 187, 102, 118, 102, 103, 57, 51, 54, 99, 48, 107, 112, 102, 58,
+            99, 111, 110, 114, 97, 100, 46, 108, 117, 100, 103, 97, 116, 101, 192,
+        ];
+
+        // some other version
+        let bytes_v1 = [
+            205, 1, 0, 153, 217, 32, 54, 54, 100, 49, 54, 99, 98, 101, 101, 55, 99, 100, 52, 55,
+            53, 51, 56, 101, 53, 99, 53, 98, 56, 98, 52, 52, 101, 57, 48, 48, 54, 101, 207, 23, 99,
+            98, 117, 24, 210, 246, 128, 206, 2, 238, 210, 240, 0, 170, 103, 105, 116, 32, 115, 116,
+            97, 116, 117, 115, 217, 42, 47, 85, 115, 101, 114, 115, 47, 99, 111, 110, 114, 97, 100,
+            46, 108, 117, 100, 103, 97, 116, 101, 47, 68, 111, 99, 117, 109, 101, 110, 116, 115,
+            47, 99, 111, 100, 101, 47, 97, 116, 117, 105, 110, 217, 32, 98, 57, 55, 100, 57, 97,
+            51, 48, 54, 102, 50, 55, 52, 52, 55, 51, 97, 50, 48, 51, 100, 50, 101, 98, 97, 52, 49,
+            102, 57, 52, 53, 55, 187, 102, 118, 102, 103, 57, 51, 54, 99, 48, 107, 112, 102, 58,
+            99, 111, 110, 114, 97, 100, 46, 108, 117, 100, 103, 97, 116, 101, 192,
+        ];
+
+        let deserialized = History::deserialize(&bytes_v0, HISTORY_VERSION);
+        assert!(deserialized.is_ok());
+
+        let deserialized = History::deserialize(&bytes_v1, HISTORY_VERSION);
+        assert!(deserialized.is_err());
+    }
 }
diff --git a/atuin-client/src/history/store.rs b/atuin-client/src/history/store.rs
new file mode 100644
index 00000000..bf74a0a8
--- /dev/null
+++ b/atuin-client/src/history/store.rs
@@ -0,0 +1,219 @@
+use eyre::{bail, eyre, Result};
+use rmp::decode::Bytes;
+
+use crate::record::{encryption::PASETO_V4, sqlite_store::SqliteStore, store::Store};
+use atuin_common::record::{DecryptedData, Host, HostId, Record, RecordIdx};
+
+use super::{History, HISTORY_TAG, HISTORY_VERSION};
+
+#[derive(Debug)]
+pub struct HistoryStore {
+    pub store: SqliteStore,
+    pub host_id: HostId,
+    pub encryption_key: [u8; 32],
+}
+
+#[derive(Debug, Eq, PartialEq, Clone)]
+pub enum HistoryRecord {
+    Create(History), // Create a history record
+    Delete(String),  // Delete a history record, identified by ID
+}
+
+impl HistoryRecord {
+    /// Serialize a history record, returning DecryptedData
+    /// The record will be of a certain type
+    /// We map those like so:
+    ///
+    /// HistoryRecord::Create -> 0
+    /// HistoryRecord::Delete-> 1
+    ///
+    /// This numeric identifier is then written as the first byte to the buffer. For history, we
+    /// append the serialized history right afterwards, to avoid having to handle serialization
+    /// twice.
+    ///
+    /// Deletion simply refers to the history by ID
+    pub fn serialize(&self) -> Result<DecryptedData> {
+        // probably don't actually need to use rmp here, but if we ever need to extend it, it's a
+        // nice wrapper around raw byte stuff
+        use rmp::encode;
+
+        let mut output = vec![];
+
+        match self {
+            HistoryRecord::Create(history) => {
+                // 0 -> a history create
+                encode::write_u8(&mut output, 0)?;
+
+                let bytes = history.serialize()?;
+
+                encode::write_bin(&mut output, &bytes.0)?;
+            }
+            HistoryRecord::Delete(id) => {
+                // 1 -> a history delete
+                encode::write_u8(&mut output, 1)?;
+                encode::write_str(&mut output, id)?;
+            }
+        };
+
+        Ok(DecryptedData(output))
+    }
+
+    pub fn deserialize(bytes: &[u8], version: &str) -> Result<Self> {
+        use rmp::decode;
+
+        fn error_report<E: std::fmt::Debug>(err: E) -> eyre::Report {
+            eyre!("{err:?}")
+        }
+
+        let mut bytes = Bytes::new(bytes);
+
+        let record_type = decode::read_u8(&mut bytes).map_err(error_report)?;
+
+        match record_type {
+            // 0 -> HistoryRecord::Create
+            0 => {
+                // not super useful to us atm, but perhaps in the future
+                // written by write_bin above
+                let _ = decode::read_bin_len(&mut bytes).map_err(error_report)?;
+
+                let record = History::deserialize(bytes.remaining_slice(), version)?;
+
+                Ok(HistoryRecord::Create(record))
+            }
+
+            // 1 -> HistoryRecord::Delete
+            1 => {
+                let bytes = bytes.remaining_slice();
+                let (id, bytes) = decode::read_str_from_slice(bytes).map_err(error_report)?;
+
+                if !bytes.is_empty() {
+                    bail!(
+                        "trailing bytes decoding HistoryRecord::Delete - malformed? got {bytes:?}"
+                    );
+                }
+
+                Ok(HistoryRecord::Delete(id.to_string()))
+            }
+
+            n => {
+                bail!("unknown HistoryRecord type {n}")
+            }
+        }
+    }
+}
+
+impl HistoryStore {
+    pub fn new(store: SqliteStore, host_id: HostId, encryption_key: [u8; 32]) -> Self {
+        HistoryStore {
+            store,
+            host_id,
+            encryption_key,
+        }
+    }
+
+    async fn push_record(&self, record: HistoryRecord) -> Result<RecordIdx> {
+        let bytes = record.serialize()?;
+        let idx = self
+            .store
+            .last(self.host_id, HISTORY_TAG)
+            .await?
+            .map_or(0, |p| p.idx + 1);
+
+        let record = Record::builder()
+            .host(Host::new(self.host_id))
+            .version(HISTORY_VERSION.to_string())
+            .tag(HISTORY_TAG.to_string())
+            .idx(idx)
+            .data(bytes)
+            .build();
+
+        self.store
+            .push(&record.encrypt::<PASETO_V4>(&self.encryption_key))
+            .await?;
+
+        Ok(idx)
+    }
+
+    pub async fn delete(&self, id: String) -> Result<RecordIdx> {
+        let record = HistoryRecord::Delete(id);
+
+        self.push_record(record).await
+    }
+
+    pub async fn push(&self, history: History) -> Result<RecordIdx> {
+        // TODO(ellie): move the history store to its own file
+        // it's tiny rn so fine as is
+        let record = HistoryRecord::Create(history);
+
+        self.push_record(record).await
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use time::macros::datetime;
+
+    use crate::history::{store::HistoryRecord, HISTORY_VERSION};
+
+    use super::History;
+
+    #[test]
+    fn test_serialize_deserialize_create() {
+        let bytes = [
+            204, 0, 196, 141, 205, 0, 0, 153, 217, 32, 48, 49, 56, 99, 100, 52, 102, 101, 56, 49,
+            55, 53, 55, 99, 100, 50, 97, 101, 101, 54, 53, 99, 100, 55, 56, 54, 49, 102, 57, 99,
+            56, 49, 207, 23, 166, 251, 212, 181, 82, 0, 0, 100, 0, 162, 108, 115, 217, 41, 47, 85,
+            115, 101, 114, 115, 47, 101, 108, 108, 105, 101, 47, 115, 114, 99, 47, 103, 105, 116,
+            104, 117, 98, 46, 99, 111, 109, 47, 97, 116, 117, 105, 110, 115, 104, 47, 97, 116, 117,
+            105, 110, 217, 32, 48, 49, 56, 99, 100, 52, 102, 101, 97, 100, 56, 57, 55, 53, 57, 55,
+            56, 53, 50, 53, 50, 55, 97, 51, 49, 99, 57, 57, 56, 48, 53, 57, 170, 98, 111, 111, 112,
+            58, 101, 108, 108, 105, 101, 192,
+        ];
+
+        let history = History {
+            id: "018cd4fe81757cd2aee65cd7861f9c81".to_owned(),
+            timestamp: datetime!(2024-01-04 00:00:00.000000 +00:00),
+            duration: 100,
+            exit: 0,
+            command: "ls".to_owned(),
+            cwd: "/Users/ellie/src/github.com/atuinsh/atuin".to_owned(),
+            session: "018cd4fead897597852527a31c998059".to_owned(),
+            hostname: "boop:ellie".to_owned(),
+            deleted_at: None,
+        };
+
+        let record = HistoryRecord::Create(history);
+
+        let serialized = record.serialize().expect("failed to serialize history");
+        assert_eq!(serialized.0, bytes);
+
+        let deserialized = HistoryRecord::deserialize(&serialized.0, HISTORY_VERSION)
+            .expect("failed to deserialize HistoryRecord");
+        assert_eq!(deserialized, record);
+
+        // check the snapshot too
+        let deserialized = HistoryRecord::deserialize(&bytes, HISTORY_VERSION)
+            .expect("failed to deserialize HistoryRecord");
+        assert_eq!(deserialized, record);
+    }
+
+    #[test]
+    fn test_serialize_deserialize_delete() {
+        let bytes = [
+            204, 1, 217, 32, 48, 49, 56, 99, 100, 52, 102, 101, 56, 49, 55, 53, 55, 99, 100, 50,
+            97, 101, 101, 54, 53, 99, 100, 55, 56, 54, 49, 102, 57, 99, 56, 49,
+        ];
+        let record = HistoryRecord::Delete("018cd4fe81757cd2aee65cd7861f9c81".to_string());
+
+        let serialized = record.serialize().expect("failed to serialize history");
+        assert_eq!(serialized.0, bytes);
+
+        let deserialized = HistoryRecord::deserialize(&serialized.0, HISTORY_VERSION)
+            .expect("failed to deserialize HistoryRecord");
+        assert_eq!(deserialized, record);
+
+        let deserialized = HistoryRecord::deserialize(&bytes, HISTORY_VERSION)
+            .expect("failed to deserialize HistoryRecord");
+        assert_eq!(deserialized, record);
+    }
+}
diff --git a/atuin-client/src/kv.rs b/atuin-client/src/kv.rs
index 1ca6b5e8..cee7063d 100644
--- a/atuin-client/src/kv.rs
+++ b/atuin-client/src/kv.rs
@@ -1,6 +1,6 @@
 use std::collections::BTreeMap;
 
-use atuin_common::record::{DecryptedData, HostId};
+use atuin_common::record::{DecryptedData, Host, HostId};
 use eyre::{bail, ensure, eyre, Result};
 use serde::Deserialize;
 
@@ -89,7 +89,7 @@ impl KvStore {
 
     pub async fn set(
         &self,
-        store: &mut (impl Store + Send + Sync),
+        store: &(impl Store + Send + Sync),
         encryption_key: &[u8; 32],
         host_id: HostId,
         namespace: &str,
@@ -111,13 +111,16 @@ impl KvStore {
 
         let bytes = record.serialize()?;
 
-        let parent = store.tail(host_id, KV_TAG).await?.map(|entry| entry.id);
+        let idx = store
+            .last(host_id, KV_TAG)
+            .await?
+            .map_or(0, |entry| entry.idx + 1);
 
         let record = atuin_common::record::Record::builder()
-            .host(host_id)
+            .host(Host::new(host_id))
             .version(KV_VERSION.to_string())
             .tag(KV_TAG.to_string())
-            .parent(parent)
+            .idx(idx)
             .data(bytes)
             .build();
 
@@ -137,43 +140,18 @@ impl KvStore {
         namespace: &str,
         key: &str,
     ) -> Result<Option<KvRecord>> {
-        // Currently, this is O(n). When we have an actual KV store, it can be better
-        // Just a poc for now!
+        // TODO: don't rebuild every time...
+        let map = self.build_kv(store, encryption_key).await?;
 
-        // iterate records to find the value we want
-        // start at the end, so we get the most recent version
-        let tails = store.tag_tails(KV_TAG).await?;
+        let res = map.get(namespace);
 
-        if tails.is_empty() {
-            return Ok(None);
-        }
-
-        // first, decide on a record.
-        // try getting the newest first
-        // we always need a way of deciding the "winner" of a write
-        // TODO(ellie): something better than last-write-wins, what if two write at the same time?
-        let mut record = tails.iter().max_by_key(|r| r.timestamp).unwrap().clone();
-
-        loop {
-            let decrypted = match record.version.as_str() {
-                KV_VERSION => record.decrypt::<PASETO_V4>(encryption_key)?,
-                version => bail!("unknown version {version:?}"),
-            };
-
-            let kv = KvRecord::deserialize(&decrypted.data, &decrypted.version)?;
-            if kv.key == key && kv.namespace == namespace {
-                return Ok(Some(kv));
-            }
+        if let Some(ns) = res {
+            let value = ns.get(key);
 
-            if let Some(parent) = decrypted.parent {
-                record = store.get(parent).await?;
-            } else {
-                break;
-            }
+            Ok(value.cloned())
+        } else {
+            Ok(None)
         }
-
-        // if we get here, then... we didn't find the record with that key :(
-        Ok(None)
     }
 
     // Build a kv map out of the linked list kv store
@@ -184,32 +162,30 @@ impl KvStore {
         &self,
         store: &impl Store,
         encryption_key: &[u8; 32],
-    ) -> Result<BTreeMap<String, BTreeMap<String, String>>> {
+    ) -> Result<BTreeMap<String, BTreeMap<String, KvRecord>>> {
         let mut map = BTreeMap::new();
-        let tails = store.tag_tails(KV_TAG).await?;
-
-        if tails.is_empty() {
-            return Ok(map);
-        }
 
-        let mut record = tails.iter().max_by_key(|r| r.timestamp).unwrap().clone();
+        // TODO: maybe don't load the entire tag into memory to build the kv
+        // we can be smart about it and only load values since the last build
+        // or, iterate/paginate
+        let tagged = store.all_tagged(KV_TAG).await?;
 
-        loop {
+        // iterate through all tags and play each KV record at a time
+        // this is "last write wins"
+        // probably good enough for now, but revisit in future
+        for record in tagged {
             let decrypted = match record.version.as_str() {
                 KV_VERSION => record.decrypt::<PASETO_V4>(encryption_key)?,
                 version => bail!("unknown version {version:?}"),
             };
 
-            let kv = KvRecord::deserialize(&decrypted.data, &decrypted.version)?;
+            let kv = KvRecord::deserialize(&decrypted.data, KV_VERSION)?;
 
-            let ns = map.entry(kv.namespace).or_insert_with(BTreeMap::new);
-            ns.entry(kv.key).or_insert_with(|| kv.value);
+            let ns = map
+                .entry(kv.namespace.clone())
+                .or_insert_with(BTreeMap::new);
 
-            if let Some(parent) = decrypted.parent {
-                record = store.get(parent).await?;
-            } else {
-                break;
-            }
+            ns.insert(kv.key.clone(), kv);
         }
 
         Ok(map)
@@ -261,19 +237,27 @@ mod tests {
         let map = kv.build_kv(&store, &key).await.unwrap();
 
         assert_eq!(
-            map.get("test-kv")
+            *map.get("test-kv")
                 .expect("map namespace not set")
                 .get("foo")
                 .expect("map key not set"),
-            "bar"
+            KvRecord {
+                namespace: String::from("test-kv"),
+                key: String::from("foo"),
+                value: String::from("bar")
+            }
         );
 
         assert_eq!(
-            map.get("test-kv")
+            *map.get("test-kv")
                 .expect("map namespace not set")
                 .get("1")
                 .expect("map key not set"),
-            "2"
+            KvRecord {
+                namespace: String::from("test-kv"),
+                key: String::from("1"),
+                value: String::from("2")
+            }
         );
     }
 }
diff --git a/atuin-client/src/record/encryption.rs b/atuin-client/src/record/encryption.rs
index 3074a9c2..c2cdaa6a 100644
--- a/atuin-client/src/record/encryption.rs
+++ b/atuin-client/src/record/encryption.rs
@@ -1,5 +1,5 @@
 use atuin_common::record::{
-    AdditionalData, DecryptedData, EncryptedData, Encryption, HostId, RecordId,
+    AdditionalData, DecryptedData, EncryptedData, Encryption, HostId, RecordId, RecordIdx,
 };
 use base64::{engine::general_purpose, Engine};
 use eyre::{ensure, Context, Result};
@@ -170,10 +170,10 @@ struct AtuinFooter {
 #[derive(Debug, Copy, Clone, Serialize)]
 struct Assertions<'a> {
     id: &'a RecordId,
+    idx: &'a RecordIdx,
     version: &'a str,
     tag: &'a str,
     host: &'a HostId,
-    parent: Option<&'a RecordId>,
 }
 
 impl<'a> From<AdditionalData<'a>> for Assertions<'a> {
@@ -183,7 +183,7 @@ impl<'a> From<AdditionalData<'a>> for Assertions<'a> {
             version: ad.version,
             tag: ad.tag,
             host: ad.host,
-            parent: ad.parent,
+            idx: ad.idx,
         }
     }
 }
@@ -196,7 +196,10 @@ impl Assertions<'_> {
 
 #[cfg(test)]
 mod tests {
-    use atuin_common::{record::Record, utils::uuid_v7};
+    use atuin_common::{
+        record::{Host, Record},
+        utils::uuid_v7,
+    };
 
     use super::*;
 
@@ -209,7 +212,7 @@ mod tests {
             version: "v0",
             tag: "kv",
             host: &HostId(uuid_v7()),
-            parent: None,
+            idx: &0,
         };
 
         let data = DecryptedData(vec![1, 2, 3, 4]);
@@ -228,7 +231,7 @@ mod tests {
             version: "v0",
             tag: "kv",
             host: &HostId(uuid_v7()),
-            parent: None,
+            idx: &0,
         };
 
         let data = DecryptedData(vec![1, 2, 3, 4]);
@@ -252,7 +255,7 @@ mod tests {
             version: "v0",
             tag: "kv",