refactor: remove pre_encrypt_mime_hook

It is only used in a single test
and the test is more reliable by having a blob .eml
that will not be accidentally modified
by mimefactory changes.

src/config.rs

@@ -452,11 +452,6 @@ pub enum Config {
     /// storing the same token multiple times on the server.
     EncryptedDeviceToken,
 
-    /// Enables running test hooks, e.g. see `InnerContext::pre_encrypt_mime_hook`.
-    /// This way is better than conditional compilation, i.e. `#[cfg(test)]`, because tests not
-    /// using this still run unmodified code.
-    TestHooks,
-
     /// Return an error from `receive_imf_inner()`. For tests.
     SimulateReceiveImfError,
 

src/context.rs

@@ -332,17 +332,6 @@ pub struct InnerContext {
     /// `Connectivity` values for mailboxes, unordered. Used to compute the aggregate connectivity,
     /// see [`Context::get_connectivity()`].
     pub(crate) connectivities: parking_lot::Mutex<Vec<ConnectivityStore>>,
-
-    #[expect(clippy::type_complexity)]
-    /// Transforms the root of the cryptographic payload before encryption.
-    pub(crate) pre_encrypt_mime_hook: parking_lot::Mutex<
-        Option<
-            for<'a> fn(
-                &Context,
-                mail_builder::mime::MimePart<'a>,
-            ) -> mail_builder::mime::MimePart<'a>,
-        >,
-    >,
 }
 
 /// The state of ongoing process.
@@ -522,7 +511,6 @@ impl Context {
             self_fingerprint: OnceLock::new(),
             self_public_key: Mutex::new(None),
             connectivities: parking_lot::Mutex::new(Vec::new()),
-            pre_encrypt_mime_hook: None.into(),
         };
 
         let ctx = Context {

src/mimefactory.rs

@@ -1168,12 +1168,6 @@ impl MimeFactory {
                 _ => None,
             };
 
-            if context.get_config_bool(Config::TestHooks).await?
-                && let Some(hook) = &*context.pre_encrypt_mime_hook.lock()
-            {
-                message = hook(context, message);
-            }
-
             let encrypted = if let Some(shared_secret) = shared_secret {
                 let sign = true;
                 encrypt_helper

src/mimeparser/mimeparser_tests.rs

@@ -1790,35 +1790,27 @@ async fn test_time_in_future() -> Result<()> {
     Ok(())
 }
 
+/// Tests receiving a message with RFC 9788 header protection and legacy display element.
+///
+/// Legacy display elements should not be rendered:
+/// <https://www.rfc-editor.org/rfc/rfc9788.html#name-do-not-render-legacy-displa>
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn test_hp_legacy_display() -> Result<()> {
     let mut tcm = TestContextManager::new();
-    let alice = &tcm.alice().await;
     let bob = &tcm.bob().await;
 
-    let mut msg = Message::new_text(
-        "Subject: Dinner plans\n\
-        \n\
-        Let's eat"
-            .to_string(),
-    );
-    msg.set_subject("Dinner plans".to_string());
-    let chat_id = alice.create_chat(bob).await.id;
-    alice.set_config_bool(Config::TestHooks, true).await?;
-    *alice.pre_encrypt_mime_hook.lock() = Some(|_, mut mime| {
-        for (h, v) in &mut mime.headers {
-            if h == "Content-Type"
-                && let mail_builder::headers::HeaderType::ContentType(ct) = v
-            {
-                *ct = ct.clone().attribute("hp-legacy-display", "1");
-            }
-        }
-        mime
-    });
-    let sent_msg = alice.send_msg(chat_id, &mut msg).await;
-
-    let msg_bob = bob.recv_msg(&sent_msg).await;
+    let msg_id = receive_imf(
+        bob,
+        include_bytes!("../../test-data/message/hp_legacy_display.eml"),
+        false,
+    )
+    .await?
+    .unwrap()
+    .msg_ids[0];
+    let msg_bob = Message::load_from_db(bob, msg_id).await?;
     assert_eq!(msg_bob.subject, "Dinner plans");
+
+    // Legacy display element is removed from the text/plain body.
     assert_eq!(msg_bob.text, "Let's eat");
     Ok(())
 }