diff --git a/android/app/src/main/AndroidManifest.xml b/android/app/src/main/AndroidManifest.xml
index d3b079f..33abf1b 100644
--- a/android/app/src/main/AndroidManifest.xml
+++ b/android/app/src/main/AndroidManifest.xml
@@ -90,6 +90,14 @@
     <uses-permission android:name="android.permission.SCHEDULE_EXACT_ALARM" />
     <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
 
+    <!--
+      allowBackup stays true, which family idea #5105 (practice 12) says to turn
+      off. Inkwell is local-first, so an unlinked phone's notes exist only on the
+      phone, and Android's backup is their one other copy. The device token is what
+      the practice protects, and it is stored sealed under a Keystore key that never
+      leaves the phone (KeystoreTokenSeal.kt). A backup therefore carries the notes
+      and a token nothing can open, and a restored app asks to sign in again.
+    -->
     <application
         android:name=".InkwellApplication"
         android:allowBackup="true"
diff --git a/android/app/src/main/java/com/fabledsword/inkwell/InkwellApplication.kt b/android/app/src/main/java/com/fabledsword/inkwell/InkwellApplication.kt
index bdd900b..b52ba71 100644
--- a/android/app/src/main/java/com/fabledsword/inkwell/InkwellApplication.kt
+++ b/android/app/src/main/java/com/fabledsword/inkwell/InkwellApplication.kt
@@ -40,7 +40,7 @@ class InkwellApplication : Application() {
         setClientAgent("inkwell-android", installedVersionName() ?: "unknown")
 
         try {
-            val handle = Inkwell(filesDir.absolutePath)
+            val handle = Inkwell(filesDir.absolutePath, KeystoreTokenSeal())
             core = handle
             Log.i(TAG, "local store ready — ${handle.summary()}")
         } catch (e: Exception) {
diff --git a/android/app/src/main/java/com/fabledsword/inkwell/KeystoreTokenSeal.kt b/android/app/src/main/java/com/fabledsword/inkwell/KeystoreTokenSeal.kt
new file mode 100644
index 0000000..7c99759
--- /dev/null
+++ b/android/app/src/main/java/com/fabledsword/inkwell/KeystoreTokenSeal.kt
@@ -0,0 +1,98 @@
+package com.fabledsword.inkwell
+
+import android.security.keystore.KeyGenParameterSpec
+import android.security.keystore.KeyProperties
+import android.util.Log
+import com.fabledsword.inkwell.core.TokenSeal
+import java.security.KeyStore
+import java.util.Base64
+import javax.crypto.Cipher
+import javax.crypto.KeyGenerator
+import javax.crypto.SecretKey
+import javax.crypto.spec.GCMParameterSpec
+
+/**
+ * Keeps the device token sealed under a key in the Android Keystore (family idea
+ * #5105, practice 12). The core stores what this returns, never the token itself.
+ *
+ * The key never leaves this phone, so a copy of the app's files yields a token
+ * nothing can open. That includes Android's backup, which stays on: an unlinked
+ * phone's notes exist only here, and a backup is their one other copy. Restored
+ * onto another phone, the notes come back and the app asks to sign in again.
+ *
+ * Both methods answer null rather than throw, because an exception crossing into
+ * the core would be a panic there. The core reads null from [sealToken] as "store
+ * it as is for now" and from [openToken] as "sign in again".
+ *
+ * Shaped after Minstrel's KeystoreSessionVault (Scribe snippet #5025).
+ */
+class KeystoreTokenSeal : TokenSeal {
+    override fun sealToken(token: String): String? =
+        runCatching { SealedBox.seal(key(), token) }
+            .onFailure { Log.w(TAG, "couldn't seal the device token", it) }
+            .getOrNull()
+
+    override fun openToken(sealed: String): String? =
+        runCatching { SealedBox.open(key(), sealed) }
+            .onFailure { Log.w(TAG, "the device token won't open on this phone", it) }
+            .getOrNull()
+
+    private fun key(): SecretKey {
+        val store = KeyStore.getInstance(KEYSTORE).apply { load(null) }
+        (store.getKey(ALIAS, null) as? SecretKey)?.let { return it }
+        val generator = KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, KEYSTORE)
+        generator.init(
+            KeyGenParameterSpec
+                .Builder(ALIAS, KeyProperties.PURPOSE_ENCRYPT or KeyProperties.PURPOSE_DECRYPT)
+                .setBlockModes(KeyProperties.BLOCK_MODE_GCM)
+                .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_NONE)
+                .setKeySize(KEY_BITS)
+                .build(),
+        )
+        return generator.generateKey()
+    }
+
+    private companion object {
+        const val TAG = "Inkwell"
+        const val KEYSTORE = "AndroidKeyStore"
+        const val ALIAS = "inkwell-device-token"
+        const val KEY_BITS = 256
+    }
+}
+
+/**
+ * AES-GCM with a fresh IV per seal, the IV stored in front of the ciphertext. Split
+ * from the Keystore so it can be tested on the JVM with an ordinary key.
+ */
+internal object SealedBox {
+    private const val TRANSFORMATION = "AES/GCM/NoPadding"
+    private const val TAG_BITS = 128
+    private const val IV_BYTES = 12
+
+    // Binds a sealed value to what it is, so it can't be passed off as another secret.
+    private val AAD = "inkwell-device-token-v1".toByteArray(Charsets.UTF_8)
+
+    fun seal(
+        key: SecretKey,
+        plaintext: String,
+    ): String {
+        val cipher = Cipher.getInstance(TRANSFORMATION)
+        // The provider picks a random IV; the Keystore refuses a caller-chosen one.
+        cipher.init(Cipher.ENCRYPT_MODE, key)
+        cipher.updateAAD(AAD)
+        val sealed = cipher.iv + cipher.doFinal(plaintext.toByteArray(Charsets.UTF_8))
+        return Base64.getEncoder().encodeToString(sealed)
+    }
+
+    fun open(
+        key: SecretKey,
+        sealed: String,
+    ): String {
+        val bytes = Base64.getDecoder().decode(sealed)
+        require(bytes.size > IV_BYTES) { "sealed value too short" }
+        val cipher = Cipher.getInstance(TRANSFORMATION)
+        cipher.init(Cipher.DECRYPT_MODE, key, GCMParameterSpec(TAG_BITS, bytes, 0, IV_BYTES))
+        cipher.updateAAD(AAD)
+        return String(cipher.doFinal(bytes, IV_BYTES, bytes.size - IV_BYTES), Charsets.UTF_8)
+    }
+}
diff --git a/android/app/src/test/java/com/fabledsword/inkwell/SealedBoxTest.kt b/android/app/src/test/java/com/fabledsword/inkwell/SealedBoxTest.kt
new file mode 100644
index 0000000..9d22126
--- /dev/null
+++ b/android/app/src/test/java/com/fabledsword/inkwell/SealedBoxTest.kt
@@ -0,0 +1,38 @@
+package com.fabledsword.inkwell
+
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNotEquals
+import org.junit.Assert.assertThrows
+import org.junit.Test
+import javax.crypto.KeyGenerator
+import javax.crypto.SecretKey
+
+class SealedBoxTest {
+    private fun aesKey(): SecretKey = KeyGenerator.getInstance("AES").apply { init(256) }.generateKey()
+
+    @Test
+    fun `a sealed token opens with the key that sealed it`() {
+        val key = aesKey()
+        val sealed = SealedBox.seal(key, "tok-1")
+        assertNotEquals("tok-1", sealed)
+        assertEquals("tok-1", SealedBox.open(key, sealed))
+    }
+
+    @Test
+    fun `sealing twice gives two different values`() {
+        // A fresh IV each time, so equal tokens can't be spotted in the file.
+        val key = aesKey()
+        assertNotEquals(SealedBox.seal(key, "tok-1"), SealedBox.seal(key, "tok-1"))
+    }
+
+    @Test
+    fun `another key can't open it, as on a phone the backup was restored to`() {
+        val sealed = SealedBox.seal(aesKey(), "tok-1")
+        assertThrows(Exception::class.java) { SealedBox.open(aesKey(), sealed) }
+    }
+
+    @Test
+    fun `a value that was never sealed is refused`() {
+        assertThrows(Exception::class.java) { SealedBox.open(aesKey(), "dG9vIHNob3J0") }
+    }
+}
diff --git a/android/ffi/src/lib.rs b/android/ffi/src/lib.rs
index 7ee734e..e7a2aad 100644
--- a/android/ffi/src/lib.rs
+++ b/android/ffi/src/lib.rs
@@ -104,15 +104,46 @@ impl CoreError {
     }
 }
 
+/// Seals the device token before it is stored, and opens it when it is read: Kotlin's
+/// half of [`state::TokenSeal`] (family idea #5105, practice 12).
+///
+/// Implemented with a key in the Android Keystore. The key never leaves the phone,
+/// so a copy of the app's files carries a token nothing else can open. That includes
+/// Android's own backup, which stays on because an unlinked phone's notes exist only
+/// there. Restored onto another phone, the app asks to sign in again.
+///
+/// Return null rather than throw: an exception escaping into the core would be a
+/// panic there.
+#[uniffi::export(with_foreign)]
+pub trait TokenSeal: Send + Sync {
+    /// The token sealed for storage, or null when that isn't possible right now.
+    fn seal_token(&self, token: String) -> Option<String>;
+    /// The sealed token opened, or null when this phone can't open it.
+    fn open_token(&self, sealed: String) -> Option<String>;
+}
+
+/// Kotlin's seal, as the core asks for one.
+struct ForeignSeal(Arc<dyn TokenSeal>);
+
+impl state::TokenSeal for ForeignSeal {
+    fn seal(&self, token: &str) -> Option<String> {
+        self.0.seal_token(token.to_string())
+    }
+    fn open(&self, sealed: &str) -> Option<String> {
+        self.0.open_token(sealed.to_string())
+    }
+}
+
 /// The client handle: the on-device store plus the attachment directory beside it.
 ///
-/// Held by Kotlin for the process lifetime. Both halves are `Send + Sync` — the store
-/// behind its mutex, the blob store being a path — which is what lets uniffi share
-/// one instance across coroutines.
+/// Held by Kotlin for the process lifetime. Every part is `Send + Sync` (the store
+/// behind its mutex, the blob store being a path, the seal by its trait bound),
+/// which is what lets uniffi share one instance across coroutines.
 #[derive(uniffi::Object)]
 pub struct Inkwell {
     db: Db,
     blobs: BlobStore,
+    seal: ForeignSeal,
 }
 
 #[uniffi::export]
@@ -124,8 +155,11 @@ impl Inkwell {
     /// storage is; the core must not guess at a platform path. The layout inside is
     /// the core's business and matches the desktop's exactly — `inkwell.db` and
     /// `blobs/` — so a store is readable by any client that opens it.
+    ///
+    /// `seal` is required rather than set later, so there is no moment in which a
+    /// token could be stored unsealed by a caller that forgot.
     #[uniffi::constructor]
-    pub fn new(data_dir: String) -> Result<Arc<Self>, CoreError> {
+    pub fn new(data_dir: String, seal: Arc<dyn TokenSeal>) -> Result<Arc<Self>, CoreError> {
         let dir = PathBuf::from(data_dir);
         std::fs::create_dir_all(&dir).map_err(CoreError::store)?;
 
@@ -133,7 +167,11 @@ impl Inkwell {
         log::info!("local store ready — {}", local::summary(&db));
 
         let blobs = BlobStore::new(dir.join("blobs")).map_err(CoreError::store)?;
-        Ok(Arc::new(Inkwell { db, blobs }))
+        Ok(Arc::new(Inkwell {
+            db,
+            blobs,
+            seal: ForeignSeal(seal),
+        }))
     }
 
     /// A one-line count summary, for the boot log.
@@ -506,11 +544,12 @@ impl Inkwell {
     pub async fn unlink(&self) -> Result<RevokeOutcome, CoreError> {
         // Read and release before the network call: a std MutexGuard isn't Send, so
         // it cannot be held across an await, and holding the store through a
-        // round-trip would freeze every note operation in the UI.
-        let link = {
-            let conn = self.db.conn().map_err(CoreError::store)?;
-            let current = state::read(&conn).map_err(CoreError::store)?;
-            current.server_url.zip(current.device_token)
+        // round-trip would freeze every note operation in the UI. A token that won't
+        // open on this phone can't be revoked from here, so it is skipped.
+        let link = match self.credentials() {
+            Ok(link) => Some(link),
+            Err(CoreError::NotLinked) => None,
+            Err(e) => return Err(e),
         };
         let revoked = match &link {
             Some((base_url, token)) => client::revoke_self(base_url, token).await,
@@ -699,12 +738,18 @@ pub fn body_tags(body: String) -> Vec<BodyTag> {
 impl Inkwell {
     /// The server URL + token, or the `NotLinked` state. Every networked call needs
     /// exactly this, and none of them may hold the lock past it.
+    ///
+    /// `NotLinked` also when the stored token won't open on this phone, which drops
+    /// it (`state::open_token`), so the app asks to sign in again.
     fn credentials(&self) -> Result<(String, String), CoreError> {
         let conn = self.db.conn().map_err(CoreError::store)?;
         let current = state::read(&conn).map_err(CoreError::store)?;
-        match (current.server_url, current.device_token) {
-            (Some(url), Some(token)) => Ok((url, token)),
-            _ => Err(CoreError::NotLinked),
+        let (Some(url), Some(stored)) = (current.server_url, current.device_token) else {
+            return Err(CoreError::NotLinked);
+        };
+        match state::open_token(&conn, &stored, &self.seal).map_err(CoreError::store)? {
+            Some(token) => Ok((url, token)),
+            None => Err(CoreError::NotLinked),
         }
     }
 
@@ -718,7 +763,7 @@ impl Inkwell {
         retention_days: Option<u32>,
     ) -> Result<(), CoreError> {
         let conn = self.db.conn().map_err(CoreError::store)?;
-        state::set_link(&conn, base_url, token).map_err(CoreError::store)?;
+        state::set_sealed_link(&conn, base_url, token, &self.seal).map_err(CoreError::store)?;
         if let Some(days) = retention_days {
             state::set_server_retention(&conn, days as i64).map_err(CoreError::store)?;
         }
@@ -736,6 +781,22 @@ mod tests {
     /// Process id + a counter rather than a uuid dependency: the FFI crate has no
     /// business pulling one in to name a temp folder, and this is the same approach
     /// the desktop's updater tests settled on.
+    /// A seal that can't seal: tokens are stored as they are, as on the desktop.
+    struct Plain;
+
+    impl TokenSeal for Plain {
+        fn seal_token(&self, _token: String) -> Option<String> {
+            None
+        }
+        fn open_token(&self, _sealed: String) -> Option<String> {
+            None
+        }
+    }
+
+    fn plain() -> Arc<dyn TokenSeal> {
+        Arc::new(Plain)
+    }
+
     fn scratch_dir() -> String {
         use std::sync::atomic::{AtomicU32, Ordering};
         static NEXT: AtomicU32 = AtomicU32::new(0);
@@ -761,7 +822,7 @@ mod tests {
     #[test]
     fn creates_a_store_and_round_trips_a_note() {
         let dir = scratch_dir();
-        let app = Inkwell::new(dir.clone()).expect("a fresh data dir should open");
+        let app = Inkwell::new(dir.clone(), plain()).expect("a fresh data dir should open");
 
         let created = app
             .create_note(draft("Groceries\nmilk"))
@@ -783,7 +844,7 @@ mod tests {
     #[test]
     fn a_note_is_named_by_its_first_line() {
         let dir = scratch_dir();
-        let app = Inkwell::new(dir.clone()).expect("a fresh data dir should open");
+        let app = Inkwell::new(dir.clone(), plain()).expect("a fresh data dir should open");
 
         let created = app
             .create_note(draft("just a thought"))
@@ -798,7 +859,7 @@ mod tests {
     #[test]
     fn a_note_with_only_items_is_named_by_its_first_item() {
         let dir = scratch_dir();
-        let app = Inkwell::new(dir.clone()).expect("a fresh data dir should open");
+        let app = Inkwell::new(dir.clone(), plain()).expect("a fresh data dir should open");
 
         let created = app
             .create_note(NoteDraft {
@@ -817,7 +878,7 @@ mod tests {
     #[test]
     fn syncing_unlinked_reports_not_linked() {
         let dir = scratch_dir();
-        let app = Inkwell::new(dir.clone()).expect("a fresh data dir should open");
+        let app = Inkwell::new(dir.clone(), plain()).expect("a fresh data dir should open");
 
         let status = app.sync_status().expect("status should read");
         assert!(!status.linked);
@@ -833,7 +894,7 @@ mod tests {
     #[test]
     fn ticking_an_item_rewrites_only_its_box() {
         let dir = scratch_dir();
-        let app = Inkwell::new(dir.clone()).expect("a fresh data dir should open");
+        let app = Inkwell::new(dir.clone(), plain()).expect("a fresh data dir should open");
         let note = app
             .create_note(NoteDraft {
                 body: "Packing".to_string(),
@@ -865,7 +926,7 @@ mod tests {
     #[test]
     fn setting_labels_leaves_tag_derived_ones_alone() {
         let dir = scratch_dir();
-        let app = Inkwell::new(dir.clone()).expect("a fresh data dir should open");
+        let app = Inkwell::new(dir.clone(), plain()).expect("a fresh data dir should open");
 
         let note = app
             .create_note(draft("Trip\nbook the ferry #travel"))
@@ -906,7 +967,7 @@ mod tests {
     #[test]
     fn deleting_forever_removes_the_note() {
         let dir = scratch_dir();
-        let app = Inkwell::new(dir.clone()).expect("a fresh data dir should open");
+        let app = Inkwell::new(dir.clone(), plain()).expect("a fresh data dir should open");
         let note = app.create_note(draft("Ephemeral\nbody")).expect("create");
 
         app.delete_note_forever(note.id.clone())
@@ -924,7 +985,7 @@ mod tests {
     #[test]
     fn an_attached_file_is_stored_found_and_removable() {
         let dir = scratch_dir();
-        let app = Inkwell::new(dir.clone()).expect("a fresh data dir should open");
+        let app = Inkwell::new(dir.clone(), plain()).expect("a fresh data dir should open");
         let note = app.create_note(draft("Receipt")).expect("create");
 
         let attached = app
@@ -973,7 +1034,7 @@ mod tests {
     #[test]
     fn reminders_can_be_snoozed_and_completed() {
         let dir = scratch_dir();
-        let app = Inkwell::new(dir.clone()).expect("a fresh data dir should open");
+        let app = Inkwell::new(dir.clone(), plain()).expect("a fresh data dir should open");
         let note = app.create_note(draft("Call back")).expect("create");
         assert_eq!(note.remind_at, None);
 
@@ -999,7 +1060,7 @@ mod tests {
     #[test]
     fn completing_a_recurring_reminder_moves_it_rather_than_ending_it() {
         let dir = scratch_dir();
-        let app = Inkwell::new(dir.clone()).expect("a fresh data dir should open");
+        let app = Inkwell::new(dir.clone(), plain()).expect("a fresh data dir should open");
         let note = app.create_note(draft("Water the plants")).expect("create");
 
         let armed = app
@@ -1061,7 +1122,7 @@ mod tests {
     #[test]
     fn renaming_onto_an_existing_tag_merges_into_the_older_one() {
         let dir = scratch_dir();
-        let app = Inkwell::new(dir.clone()).expect("a fresh data dir should open");
+        let app = Inkwell::new(dir.clone(), plain()).expect("a fresh data dir should open");
 
         let older = app.create_label("grocery".to_string()).expect("older");
         // `created_at` is RFC3339 to the MILLISECOND. Without a gap the two rows can
@@ -1106,7 +1167,7 @@ mod tests {
     #[test]
     fn the_rename_merge_survivor_does_not_depend_on_the_direction() {
         let dir = scratch_dir();
-        let app = Inkwell::new(dir.clone()).expect("a fresh data dir should open");
+        let app = Inkwell::new(dir.clone(), plain()).expect("a fresh data dir should open");
 
         let older = app.create_label("grocery".to_string()).expect("older");
         std::thread::sleep(std::time::Duration::from_millis(5));
diff --git a/core/src/sync/state.rs b/core/src/sync/state.rs
index 47db739..05e7bc0 100644
--- a/core/src/sync/state.rs
+++ b/core/src/sync/state.rs
@@ -8,6 +8,10 @@
 //! the `keyring` crate needs libsecret/DBus on Linux, which adds a C dependency to a
 //! binary that has to cross-compile, and fails outright on headless or minimal-WM
 //! setups. Protecting the database file is the portable trade.
+//!
+//! A client that has somewhere better to keep a key passes a [`TokenSeal`], and the
+//! token is stored sealed. Android does, with a key in the Keystore (family idea
+//! #5105, practice 12); the desktop does not.
 
 use rusqlite::{params, Connection};
 use serde::Serialize;
@@ -107,6 +111,79 @@ pub fn set_link(conn: &Connection, server_url: &str, device_token: &str) -> rusq
     Ok(())
 }
 
+/// Seals the device token for storage, and opens it again.
+///
+/// Neither method fails loudly: a client's key store can be briefly unavailable, and
+/// a token sealed on another device can never be opened here. `None` says so, and
+/// [`set_sealed_link`] and [`open_token`] decide what happens next.
+pub trait TokenSeal {
+    /// The token sealed for storage, or None when that isn't possible right now.
+    fn seal(&self, token: &str) -> Option<String>;
+    /// The sealed token opened, or None when this device can't open it.
+    fn open(&self, sealed: &str) -> Option<String>;
+}
+
+/// Marks a stored token as sealed. A device token is URL-safe base64, which has no
+/// colon, so a plain one can't be mistaken for a sealed one.
+const SEALED: &str = "sealed:";
+
+/// [`set_link`] for a client that seals its token.
+///
+/// When sealing fails, the token is stored as it is and [`open_token`] seals it on
+/// its next read. Refusing the link instead would leave someone unable to sync
+/// over a passing key-store error.
+pub fn set_sealed_link(
+    conn: &Connection,
+    server_url: &str,
+    device_token: &str,
+    seal: &dyn TokenSeal,
+) -> rusqlite::Result<()> {
+    let stored = match seal.seal(device_token) {
+        Some(sealed) => format!("{SEALED}{sealed}"),
+        None => {
+            log::warn!("couldn't seal the device token; it is stored as is until the next read");
+            device_token.to_string()
+        }
+    };
+    set_link(conn, server_url, &stored)
+}
+
+/// The device token the server expects, from the `stored` one.
+///
+/// - A sealed token is opened. If it won't open, it is dropped, so the app reads as
+///   unlinked and asks to sign in again. That is what happens when Android restores
+///   the app's files onto another phone, whose Keystore never held the key. The
+///   server address and cursor stay, for the sign-in form and the same server.
+/// - A plain token, stored before tokens were sealed or when sealing failed, is
+///   sealed in place and returned.
+pub fn open_token(
+    conn: &Connection,
+    stored: &str,
+    seal: &dyn TokenSeal,
+) -> rusqlite::Result<Option<String>> {
+    if let Some(sealed) = stored.strip_prefix(SEALED) {
+        let token = seal.open(sealed);
+        if token.is_none() {
+            log::warn!("the stored device token won't open on this device; sign in again");
+            store_token(conn, None)?;
+        }
+        return Ok(token);
+    }
+    if let Some(sealed) = seal.seal(stored) {
+        store_token(conn, Some(&format!("{SEALED}{sealed}")))?;
+    }
+    Ok(Some(stored.to_string()))
+}
+
+/// Replace the stored token alone, leaving the server and cursor as they are.
+fn store_token(conn: &Connection, token: Option<&str>) -> rusqlite::Result<()> {
+    conn.execute(
+        "UPDATE sync_state SET device_token = ?1 WHERE id = 1",
+        params![token],
+    )?;
+    Ok(())
+}
+
 /// Drop the notes other people shared with the account this device was linked to.
 /// They were only ever here through that link: kept after it ends, they would sit
 /// on the board as notes nobody here can edit and nothing would ever update.
@@ -240,6 +317,73 @@ mod tests {
         assert_eq!(state.device_token.as_deref(), Some("tok-1"));
     }
 
+    /// Reverses the token: enough to tell sealed from plain. `broken` stands in for a
+    /// key store that is unavailable, or a key this device never held.
+    struct Reverse {
+        broken: bool,
+    }
+
+    impl TokenSeal for Reverse {
+        fn seal(&self, token: &str) -> Option<String> {
+            (!self.broken).then(|| token.chars().rev().collect())
+        }
+        fn open(&self, sealed: &str) -> Option<String> {
+            (!self.broken).then(|| sealed.chars().rev().collect())
+        }
+    }
+
+    const WORKING: Reverse = Reverse { broken: false };
+    const BROKEN: Reverse = Reverse { broken: true };
+
+    fn stored_token(conn: &Connection) -> Option<String> {
+        read(conn).expect("read").device_token
+    }
+
+    #[test]
+    fn a_sealed_token_is_stored_sealed_and_opens() {
+        let conn = db();
+        set_sealed_link(&conn, "https://notes.example.com", "tok-1", &WORKING).expect("link");
+        assert_eq!(stored_token(&conn).as_deref(), Some("sealed:1-kot"));
+
+        let opened = open_token(&conn, "sealed:1-kot", &WORKING).expect("open");
+        assert_eq!(opened.as_deref(), Some("tok-1"));
+    }
+
+    #[test]
+    fn a_plain_token_is_sealed_on_its_next_read() {
+        let conn = db();
+        set_link(&conn, "https://notes.example.com", "tok-1").expect("link");
+
+        let opened = open_token(&conn, "tok-1", &WORKING).expect("open");
+        assert_eq!(opened.as_deref(), Some("tok-1"));
+        assert_eq!(stored_token(&conn).as_deref(), Some("sealed:1-kot"));
+    }
+
+    #[test]
+    fn a_token_that_cant_be_sealed_is_kept_plain_and_still_works() {
+        let conn = db();
+        set_sealed_link(&conn, "https://notes.example.com", "tok-1", &BROKEN).expect("link");
+        assert_eq!(stored_token(&conn).as_deref(), Some("tok-1"));
+        let opened = open_token(&conn, "tok-1", &BROKEN).expect("open");
+        assert_eq!(opened.as_deref(), Some("tok-1"));
+    }
+
+    #[test]
+    fn a_token_that_wont_open_here_is_dropped_but_the_server_is_kept() {
+        let conn = db();
+        set_sealed_link(&conn, "https://notes.example.com", "tok-1", &WORKING).expect("link");
+
+        let opened = open_token(&conn, "sealed:1-kot", &BROKEN).expect("open");
+        assert_eq!(opened, None);
+        let state = read(&conn).expect("read");
+        assert!(!state.is_linked());
+        assert_eq!(state.device_token, None);
+        assert_eq!(
+            state.server_url.as_deref(),
+            Some("https://notes.example.com")
+        );
+    }
+
     #[test]
     fn an_unlinked_device_uses_its_own_retention_window() {
         let conn = db();