docs: deprecate protection-broken and related stuff (#7018)

came over these parts while targeting the new info message of
https://github.com/chatmail/core/pull/7008 in
https://github.com/deltachat/deltachat-ios/pull/2778 and
https://github.com/deltachat/deltachat-android/pull/3822

---------

Co-authored-by: Hocuri <hocuri@gmx.de>

src/chat.rs

@@ -118,7 +118,7 @@ pub(crate) enum CantSendReason {
     /// The chat is a contact request, it needs to be accepted before sending a message.
     ContactRequest,
 
-    /// The chat was protected, but now a new message came in
+    /// Deprecated. The chat was protected, but now a new message came in
     /// which was not encrypted / signed correctly.
     ProtectionBroken,
 
@@ -1935,7 +1935,7 @@ impl Chat {
         Ok(is_encrypted)
     }
 
-    /// Returns true if the chat was protected, and then an incoming message broke this protection.
+    /// Deprecated 2025-07. Returns true if the chat was protected, and then an incoming message broke this protection.
     ///
     /// This function is only useful if the UI enabled the `verified_one_on_one_chats` feature flag,
     /// otherwise it will return false for all chats.

src/config.rs

@@ -417,7 +417,7 @@ pub enum Config {
     #[strum(props(default = "172800"))]
     GossipPeriod,
 
-    /// Feature flag for verified 1:1 chats; the UI should set it
+    /// Deprecated 2025-07. Feature flag for verified 1:1 chats; the UI should set it
     /// to 1 if it supports verified 1:1 chats.
     /// Regardless of this setting, `chat.is_protected()` returns true while the key is verified,
     /// and when the key changes, an info message is posted into the chat.

src/context.rs

@@ -1043,7 +1043,7 @@ impl Context {
             self.get_config_int(Config::GossipPeriod).await?.to_string(),
         );
         res.insert(
-            "verified_one_on_one_chats",
+            "verified_one_on_one_chats", // deprecated 2025-07
             self.get_config_bool(Config::VerifiedOneOnOneChats)
                 .await?
                 .to_string(),

src/imex.rs

@@ -804,7 +804,7 @@ async fn export_database(
                 "UPDATE backup.config SET value='0' WHERE keyname='verified_one_on_one_chats';",
                 [],
             )
-            .ok(); // If verified_one_on_one_chats was not set, this errors, which we ignore
+            .ok(); // Deprecated 2025-07. If verified_one_on_one_chats was not set, this errors, which we ignore
             conn.execute("DETACH DATABASE backup", [])
                 .context("failed to detach backup database")?;
             res?;