3 files changed, 96 insertions, 2 deletions

diff --git a/crates/chat-server/src/main.rs b/crates/chat-server/src/main.rs
index 6c7f4e1..c17a7f6 100644
--- a/crates/chat-server/src/main.rs
+++ b/crates/chat-server/src/main.rs
@@ -16,6 +16,7 @@
 #![doc = "Local experimental chat server with ciphertext-only durable storage."]
 
 mod http;
+mod maintenance;
 mod service;
 mod store;
 
@@ -33,8 +34,16 @@ struct Arguments {
     root: PathBuf,
     #[arg(long, default_value = "127.0.0.1:9080")]
     bind: SocketAddr,
-    #[arg(long)]
+    #[arg(long, conflicts_with_all = ["reset_owner", "owner_fingerprint", "snapshot"])]
     init: bool,
+    #[arg(long, value_name = "FINGERPRINT", conflicts_with_all = ["owner_fingerprint", "snapshot"], help = "Permanently clear the matching owner registration and all chat history after key loss")]
+    reset_owner: Option<String>,
+    #[arg(
+        long,
+        conflicts_with = "snapshot",
+        help = "Print the registered owner's public fingerprint"
+    )]
+    owner_fingerprint: bool,
     #[arg(long)]
     snapshot: Option<PathBuf>,
 }
@@ -76,11 +85,22 @@ async fn run(arguments: Arguments) -> Result<()> {
     std::fs::create_dir_all(&data)?;
     std::fs::set_permissions(&data, std::os::unix::fs::PermissionsExt::from_mode(0o700))?;
     let database = data.join("chat.sqlite");
-    let store = store::Store::open(&database)?;
+    let _server_lock = if arguments.snapshot.is_none() && !arguments.owner_fingerprint {
+        Some(maintenance::lock(&data)?)
+    } else {
+        None
+    };
+    let mut store = store::Store::open(&database)?;
     std::fs::set_permissions(
         &database,
         std::os::unix::fs::PermissionsExt::from_mode(0o600),
     )?;
+    if arguments.owner_fingerprint {
+        return maintenance::fingerprint(&store);
+    }
+    if let Some(expected) = arguments.reset_owner {
+        return maintenance::reset(&mut store, &expected, arguments.bind);
+    }
     if let Some(destination) = arguments.snapshot {
         store.snapshot(&destination)?;
         std::fs::set_permissions(
diff --git a/crates/chat-server/src/maintenance.rs b/crates/chat-server/src/maintenance.rs
new file mode 100644
index 0000000..eac689d
--- /dev/null
+++ b/crates/chat-server/src/maintenance.rs
@@ -0,0 +1,61 @@
+// Copyright (C) 2026 Doan Luu Duc Tai <doan@luuduct.ai>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as
+// published by the Free Software Foundation, either version 3 of the
+// License, or (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+use crate::store::Store;
+use anyhow::{Context, Result, ensure};
+use std::fs::{File, OpenOptions};
+use std::io::Write;
+use std::net::{SocketAddr, TcpListener};
+use std::os::unix::fs::OpenOptionsExt;
+use std::path::Path;
+
+pub(crate) fn lock(directory: &Path) -> Result<File> {
+    let file = OpenOptions::new()
+        .read(true)
+        .write(true)
+        .create(true)
+        .truncate(false)
+        .mode(0o600)
+        .open(directory.join("server.lock"))?;
+    file.try_lock().context(
+        "Chat is already running. Stop it before starting another server or resetting the owner.",
+    )?;
+    Ok(file)
+}
+
+pub(crate) fn fingerprint(store: &Store) -> Result<()> {
+    let certificate = store.owner()?.context("No owner identity is registered")?;
+    writeln!(
+        std::io::stdout().lock(),
+        "{}",
+        stack_chat_crypto::public_identity(&certificate)?
+    )?;
+    Ok(())
+}
+
+pub(crate) fn reset(store: &mut Store, expected: &str, address: SocketAddr) -> Result<()> {
+    ensure!(
+        address.ip().is_loopback(),
+        "Reset must use the local chat address"
+    );
+    let _port =
+        TcpListener::bind(address).context("Stop the chat server before resetting its owner")?;
+    store.reset_owner(expected)?;
+    writeln!(
+        std::io::stdout().lock(),
+        "Owner registration and chat history cleared. Restart chat and use OWNER SETUP to create a new owner file. Existing backup archives were not changed."
+    )?;
+    Ok(())
+}
diff --git a/crates/chat-server/src/store.rs b/crates/chat-server/src/store.rs
index fce3bb3..0e09de7 100644
--- a/crates/chat-server/src/store.rs
+++ b/crates/chat-server/src/store.rs
@@ -45,6 +45,19 @@ impl Store {
         Ok(())
     }
 
+    pub(crate) fn reset_owner(&mut self, expected: &str) -> Result<()> {
+        let owner = self.owner()?.context("No owner identity is registered")?;
+        let fingerprint = stack_chat_crypto::public_identity(&owner)?;
+        ensure!(
+            expected.len() == 64 && expected.eq_ignore_ascii_case(&fingerprint),
+            "Owner fingerprint does not match; no data was cleared"
+        );
+        let transaction = self.connection.transaction()?;
+        transaction.execute_batch("DELETE FROM messages; DELETE FROM conversations; DELETE FROM metadata WHERE key='owner'; DELETE FROM sqlite_sequence WHERE name='messages';")?;
+        transaction.commit()?;
+        Ok(())
+    }
+
     pub(crate) fn register(&self, id: &str, cert: &str) -> Result<()> {
         if self.connection.query_row(
             "SELECT EXISTS(SELECT 1 FROM conversations WHERE id=?1)",