diff --git a/Cargo.toml b/Cargo.toml
index 8faa519..dec6e1c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -14,6 +14,7 @@ version = "0.1.0"
 anyhow = "1"
 clap = { version = "4", features = ["derive"] }
 hive-sh4re = { path = "hive-sh4re" }
+rusqlite = { version = "0.37", features = ["bundled"] }
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 tokio = { version = "1", features = ["io-util", "macros", "net", "process", "rt-multi-thread", "signal", "time"] }
diff --git a/hive-c0re/Cargo.toml b/hive-c0re/Cargo.toml
index be3ed94..2d84474 100644
--- a/hive-c0re/Cargo.toml
+++ b/hive-c0re/Cargo.toml
@@ -7,6 +7,7 @@ version.workspace = true
 anyhow.workspace = true
 clap.workspace = true
 hive-sh4re.workspace = true
+rusqlite.workspace = true
 serde.workspace = true
 serde_json.workspace = true
 tokio.workspace = true
diff --git a/hive-c0re/src/agent_server.rs b/hive-c0re/src/agent_server.rs
index 89104a8..05aae47 100644
--- a/hive-c0re/src/agent_server.rs
+++ b/hive-c0re/src/agent_server.rs
@@ -83,19 +83,26 @@ async fn serve(stream: UnixStream, agent: String, broker: Arc<Broker>) -> Result
 fn dispatch(req: &AgentRequest, agent: &str, broker: &Broker) -> AgentResponse {
     match req {
         AgentRequest::Send { to, body } => {
-            broker.send(Message {
+            match broker.send(Message {
                 from: agent.to_owned(),
                 to: to.clone(),
                 body: body.clone(),
-            });
-            AgentResponse::Ok
+            }) {
+                Ok(()) => AgentResponse::Ok,
+                Err(e) => AgentResponse::Err {
+                    message: format!("{e:#}"),
+                },
+            }
         }
         AgentRequest::Recv => match broker.recv(agent) {
-            Some(msg) => AgentResponse::Message {
+            Ok(Some(msg)) => AgentResponse::Message {
                 from: msg.from,
                 body: msg.body,
             },
-            None => AgentResponse::Empty,
+            Ok(None) => AgentResponse::Empty,
+            Err(e) => AgentResponse::Err {
+                message: format!("{e:#}"),
+            },
         },
     }
 }
diff --git a/hive-c0re/src/broker.rs b/hive-c0re/src/broker.rs
index 2867c1f..0eb2555 100644
--- a/hive-c0re/src/broker.rs
+++ b/hive-c0re/src/broker.rs
@@ -1,30 +1,80 @@
-//! In-memory message broker. Phase 3 replaces this with a sqlite-backed store.
+//! Sqlite-backed message broker. Survives `hive-c0re` restart.
 
-use std::collections::{HashMap, VecDeque};
+use std::path::Path;
 use std::sync::Mutex;
+use std::time::{SystemTime, UNIX_EPOCH};
 
+use anyhow::{Context, Result};
 use hive_sh4re::Message;
+use rusqlite::{Connection, OptionalExtension, params};
+
+const SCHEMA: &str = r#"
+CREATE TABLE IF NOT EXISTS messages (
+    id           INTEGER PRIMARY KEY AUTOINCREMENT,
+    sender       TEXT    NOT NULL,
+    recipient    TEXT    NOT NULL,
+    body         TEXT    NOT NULL,
+    sent_at      INTEGER NOT NULL,
+    delivered_at INTEGER
+);
+CREATE INDEX IF NOT EXISTS idx_messages_undelivered
+    ON messages (recipient, id) WHERE delivered_at IS NULL;
+"#;
 
-#[derive(Default)]
 pub struct Broker {
-    queues: Mutex<HashMap<String, VecDeque<Message>>>,
+    conn: Mutex<Connection>,
 }
 
 impl Broker {
-    pub fn new() -> Self {
-        Self::default()
+    pub fn open(path: &Path) -> Result<Self> {
+        if let Some(parent) = path.parent() {
+            std::fs::create_dir_all(parent)
+                .with_context(|| format!("create db parent {}", parent.display()))?;
+        }
+        let conn = Connection::open(path)
+            .with_context(|| format!("open broker db {}", path.display()))?;
+        conn.execute_batch(SCHEMA).context("apply broker schema")?;
+        Ok(Self {
+            conn: Mutex::new(conn),
+        })
     }
 
-    pub fn send(&self, message: Message) {
-        let mut queues = self.queues.lock().unwrap();
-        queues
-            .entry(message.to.clone())
-            .or_default()
-            .push_back(message);
+    pub fn send(&self, message: Message) -> Result<()> {
+        let conn = self.conn.lock().unwrap();
+        conn.execute(
+            "INSERT INTO messages (sender, recipient, body, sent_at) VALUES (?1, ?2, ?3, ?4)",
+            params![message.from, message.to, message.body, now_unix()],
+        )?;
+        Ok(())
     }
 
-    pub fn recv(&self, recipient: &str) -> Option<Message> {
-        let mut queues = self.queues.lock().unwrap();
-        queues.get_mut(recipient).and_then(|q| q.pop_front())
+    pub fn recv(&self, recipient: &str) -> Result<Option<Message>> {
+        let conn = self.conn.lock().unwrap();
+        let row: Option<(i64, String, String, String)> = conn
+            .query_row(
+                "SELECT id, sender, recipient, body
+                   FROM messages
+                  WHERE recipient = ?1 AND delivered_at IS NULL
+                  ORDER BY id ASC
+                  LIMIT 1",
+                params![recipient],
+                |row| Ok((row.get(0)?, row.get(1)?, row.get(2)?, row.get(3)?)),
+            )
+            .optional()?;
+        let Some((id, from, to, body)) = row else {
+            return Ok(None);
+        };
+        conn.execute(
+            "UPDATE messages SET delivered_at = ?1 WHERE id = ?2",
+            params![now_unix(), id],
+        )?;
+        Ok(Some(Message { from, to, body }))
     }
 }
+
+fn now_unix() -> i64 {
+    SystemTime::now()
+        .duration_since(UNIX_EPOCH)
+        .map(|d| d.as_secs() as i64)
+        .unwrap_or(0)
+}
diff --git a/hive-c0re/src/coordinator.rs b/hive-c0re/src/coordinator.rs
index 105e92a..04b5e6b 100644
--- a/hive-c0re/src/coordinator.rs
+++ b/hive-c0re/src/coordinator.rs
@@ -2,7 +2,7 @@
 //! sockets: the broker plus a map of `name -> AgentSocket`.
 
 use std::collections::HashMap;
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 use std::sync::{Arc, Mutex};
 
 use anyhow::{Context, Result};
@@ -18,11 +18,12 @@ pub struct Coordinator {
 }
 
 impl Coordinator {
-    pub fn new() -> Self {
-        Self {
-            broker: Arc::new(Broker::new()),
+    pub fn open(db_path: &Path) -> Result<Self> {
+        let broker = Broker::open(db_path).context("open broker")?;
+        Ok(Self {
+            broker: Arc::new(broker),
             agents: Mutex::new(HashMap::new()),
-        }
+        })
     }
 
     pub async fn register_agent(&self, name: &str) -> Result<PathBuf> {
diff --git a/hive-c0re/src/main.rs b/hive-c0re/src/main.rs
index 760d193..6346cf9 100644
--- a/hive-c0re/src/main.rs
+++ b/hive-c0re/src/main.rs
@@ -32,6 +32,9 @@ enum Cmd {
         /// Flake reference for the agent base template.
         #[arg(long, default_value = "/etc/hyperhive#agent-base")]
         agent_flake: String,
+        /// Path to the sqlite message store.
+        #[arg(long, default_value = "/var/lib/hyperhive/broker.sqlite")]
+        db: PathBuf,
     },
     /// Spawn a new agent container (`hive-agent-<name>`).
     Spawn { name: String },
@@ -54,8 +57,8 @@ async fn main() -> Result<()> {
 
     let cli = Cli::parse();
     match cli.cmd {
-        Cmd::Serve { agent_flake } => {
-            let coord = Arc::new(Coordinator::new());
+        Cmd::Serve { agent_flake, db } => {
+            let coord = Arc::new(Coordinator::open(&db)?);
             server::serve(&cli.socket, &agent_flake, coord).await
         }
         Cmd::Spawn { name } => {