gatewayd: the texts that say who asked for a redirected approval

Implemented-By: OpenCode session (model recorded in docs/implementer-log.md)

crates/gatewayd/src/approvals/text.rs

@@ -173,3 +173,52 @@ pub fn ended_line(ended: &Ended) -> String {
 pub fn with_ending(last: &str, ended: &Ended) -> String {
     format!("{last}\n\n{}", ended_line(ended))
 }
+
+/// The most characters of an asker's message shown to the approver: it is context, not what is
+/// approved, so it may be cut.
+pub const PROMPT_SHOWN: usize = 2_000;
+
+/// Who asked for an approval that is shown elsewhere (M4b spec, section 6).
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct Asked {
+    /// `@username`, or the user id when the name could not be found.
+    pub by: String,
+    /// The channel's type: `D` a direct message, `G` a group message.
+    pub channel_type: String,
+    /// The text of the turn that asked.
+    pub prompt: String,
+}
+
+/// The first post of a redirected approval: who asked, where, and their message.
+pub fn asked_post(id: u64, asked: &Asked) -> String {
+    let place = if asked.channel_type == "G" {
+        "a group message"
+    } else {
+        "a direct message"
+    };
+    let escaped = proto::escape::escape_model_text(&asked.prompt);
+    let total = escaped.chars().count();
+    let shown: String = escaped.chars().take(PROMPT_SHOWN).collect();
+    let mut post = format!(
+        "**Approval {id}** was asked by {} in {place} with the bot. Their message:\n{}",
+        asked.by,
+        fence(&shown)
+    );
+    if total > PROMPT_SHOWN {
+        post.push_str(&format!("\n(… {} more characters)", total - PROMPT_SHOWN));
+    }
+    post
+}
+
+/// The first post of an approval whose session `gatewayd` does not follow.
+pub fn unfollowed_post(id: u64, session: &str) -> String {
+    format!(
+        "**Approval {id}** was asked in session {}, which gatewayd does not follow now (a restart, or a session from outside Mattermost).",
+        code(session)
+    )
+}
+
+/// The line left in the asking thread when its approval goes to an approver.
+pub fn sent_to_approver(id: u64) -> String {
+    format!("waiting for approval {id}: it was sent to an approver")
+}