gatewayd: approvals answered from Mattermost; typing paused; the notice

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

crates/gatewayd/src/approvals/mod.rs

@@ -3,7 +3,7 @@
 
 pub mod text;
 
-use std::collections::HashMap;
+use std::collections::{HashMap, HashSet};
 use std::sync::mpsc::Sender;
 use std::sync::{Mutex, MutexGuard};
 
@@ -44,6 +44,8 @@ pub enum Judged {
 #[derive(Debug, Default)]
 pub struct Registry {
     posted: Mutex<HashMap<u64, Posted>>,
+    /// Every approval ever posted here, answered or not: for the notice.
+    ever: Mutex<HashSet<u64>>,
 }
 
 impl Registry {
@@ -56,6 +58,10 @@ impl Registry {
     }
 
     pub fn add(&self, posted: Posted) {
+        self.ever
+            .lock()
+            .unwrap_or_else(|p| p.into_inner())
+            .insert(posted.approval);
         self.lock().insert(posted.approval, posted);
     }
 
@@ -73,6 +79,14 @@ impl Registry {
         self.lock().values().map(|p| p.session.clone()).collect()
     }
 
+    /// Was approval `id` ever posted here?
+    pub fn was_posted(&self, id: u64) -> bool {
+        self.ever
+            .lock()
+            .unwrap_or_else(|p| p.into_inner())
+            .contains(&id)
+    }
+
     /// Judge a command from `user`, posted as `post` at `at` in the thread `root`, in the order of
     /// the spec's section 7. An accepted answer is taken out and sent; nothing else changes.
     pub fn judge(