make the forge-notify cursor bound explicit: shared fetch-limit const + assert + docs (closes #2117)

hive-ag3nt/src/forge_notify.rs

@@ -28,6 +28,13 @@ use tracing::{debug, info, warn};
 
 const POLL_INTERVAL_SECS: u64 = 30;
 const HTTP_TIMEOUT_SECS: u64 = 10;
+/// Page size of the unread-notifications fetch. This is also the hard
+/// bound on the persisted delivery-dedupe cursor: each poll prunes the
+/// cursor to the ids in this window, so the `forge_cursor` field in
+/// `hyperhive-harness.json` can never exceed this many entries. Keep
+/// the two coupled — bumping the fetch limit grows the cursor's ceiling
+/// with it, deliberately and visibly.
+const UNREAD_FETCH_LIMIT: usize = 50;
 /// Maximum characters of a body/comment to include in the wake message.
 const BODY_TRUNCATE: usize = 500;
 /// How long to wait between token-read retries when the token file is
@@ -743,7 +750,7 @@ async fn poll_once(
     delivered: &mut HashMap<u64, String>,
     own_login: &str,
 ) {
-    let url = format!("{forge_url}/api/v1/notifications?all=false&limit=50");
+    let url = format!("{forge_url}/api/v1/notifications?all=false&limit={UNREAD_FETCH_LIMIT}");
     let resp = match client
         .get(&url)
         .header("Authorization", format!("token {token}"))
@@ -841,12 +848,23 @@ async fn poll_once(
     // dead weight; dropping it bounds the map to the current unread size.
     // If such a thread later goes unread again it carries a fresh
     // `updated_at` and re-delivers correctly.
+    //
+    // This retain IS the cursor's size bound: `current_ids` comes from a
+    // single `limit=UNREAD_FETCH_LIMIT` page, so the persisted cursor can
+    // never exceed that many entries — it tracks the unread *window*, not
+    // the all-time notification count. The assert makes the invariant
+    // loud in tests/dev if a future pagination change silently breaks it.
     let current_ids: HashSet<u64> = notifications
         .iter()
         .filter_map(|n| n["id"].as_u64())
         .collect();
     let before_prune = delivered.len();
     delivered.retain(|id, _| current_ids.contains(id));
+    debug_assert!(
+        delivered.len() <= UNREAD_FETCH_LIMIT,
+        "dedupe cursor exceeded the fetch window ({} > {UNREAD_FETCH_LIMIT})",
+        delivered.len(),
+    );
     if delivered.len() != before_prune {
         cursor_dirty = true;
     }