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")
+}

crates/gatewayd/tests/approvals_asked.rs

@@ -0,0 +1,86 @@
+//! The posts that tell an approver who asked for a redirected approval and what, and the line left
+//! in the asking thread (M4b spec, section 6, after the review). Do not edit.
+
+use gatewayd::approvals::text::{
+    Asked, PROMPT_SHOWN, asked_post, sent_to_approver, unfollowed_post,
+};
+
+/// The escape for one code point, built here so this file holds no such character itself.
+fn esc(code: u32) -> String {
+    format!("{}u{code:04x}", char::from(92))
+}
+
+fn asked(prompt: &str, channel_type: &str) -> Asked {
+    Asked {
+        by: "@alex".to_string(),
+        channel_type: channel_type.to_string(),
+        prompt: prompt.to_string(),
+    }
+}
+
+#[test]
+fn who_where_and_what_they_asked() {
+    assert_eq!(
+        asked_post(
+            3,
+            &asked("Read the file /srv/notes/q3.txt and summarise it.", "D")
+        ),
+        "**Approval 3** was asked by @alex in a direct message with the bot. Their message:\n```\nRead the file /srv/notes/q3.txt and summarise it.\n```"
+    );
+    let group = asked_post(4, &asked("first\n\nsecond", "G"));
+    assert_eq!(
+        group,
+        "**Approval 4** was asked by @alex in a group message with the bot. Their message:\n```\nfirst\n\nsecond\n```",
+        "a burst keeps its lines"
+    );
+}
+
+#[test]
+fn the_message_is_escaped_and_fenced() {
+    let hostile = format!(
+        "see ``` and @channel{}{}",
+        char::from_u32(0x202e).unwrap(),
+        char::from(7)
+    );
+    let post = asked_post(5, &asked(&hostile, "D"));
+    assert!(
+        post.contains(&format!(
+            "\n````\nsee ``` and @channel{}{}\n````",
+            esc(0x202e),
+            esc(7)
+        )),
+        "{post}"
+    );
+    assert!(!post.contains(char::from_u32(0x202e).unwrap()) && !post.contains(char::from(7)));
+}
+
+#[test]
+fn a_long_message_is_cut_and_says_how_much() {
+    let long = "é".repeat(PROMPT_SHOWN + 25);
+    let post = asked_post(6, &asked(&long, "D"));
+    assert!(
+        post.ends_with(&format!(
+            "\n```\n{}\n```\n(… 25 more characters)",
+            "é".repeat(PROMPT_SHOWN)
+        )),
+        "{}",
+        &post[post.len() - 80..]
+    );
+    let exact = asked_post(6, &asked(&"x".repeat(PROMPT_SHOWN), "D"));
+    assert!(
+        !exact.contains("more characters"),
+        "nothing cut, nothing said"
+    );
+}
+
+#[test]
+fn an_unfollowed_session_and_the_note() {
+    assert_eq!(
+        unfollowed_post(9, "chat-1789700000-1"),
+        "**Approval 9** was asked in session `chat-1789700000-1`, which gatewayd does not follow now (a restart, or a session from outside Mattermost)."
+    );
+    assert_eq!(
+        sent_to_approver(3),
+        "waiting for approval 3: it was sent to an approver"
+    );
+}