fix(manager-core): F-P-012 keyset cursor on app_user_repo::list (created_at, id) tiebreaker

ORDER BY created_at DESC, id DESC but cursor was `WHERE created_at <
$2` — when two users were created at the same instant, pagination
could skip the second row at a page boundary or return it twice.

- Add ListCursor { created_at, id } with `<rfc3339>_<uuid>` encode /
  decode helpers.
- Change WHERE predicate to `(created_at, id) < ($2, $3)` matching the
  ORDER BY.
- Surface the opaque cursor string through UsersListOpts /
  UsersListPage / users_admin_api ListUsersResponse instead of the raw
  DateTime — keeps the wire format stable while the id half stops the
  boundary bug.

Same shape as F-P-005 (execution_logs).

AUDIT.md anchor: F-P-012.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/manager-core/src/app_user_repo.rs

@@ -117,16 +117,48 @@ pub trait AppUserRepository: Send + Sync {
     async fn delete(&self, app_id: AppId, id: AppUserId) -> Result<bool, AppUserRepositoryError>;
 }
 
+/// F-P-012: cursor carries `(created_at, id)` for keyset pagination.
+/// Without the `id` tiebreaker, two users created at the same instant
+/// could be skipped or duplicated at a page boundary.
+#[derive(Debug, Clone, Copy)]
+pub struct ListCursor {
+    pub created_at: DateTime<Utc>,
+    pub id: picloud_shared::AppUserId,
+}
+
+impl ListCursor {
+    /// Encode as `<rfc3339>_<uuid>` — what we surface to script-land
+    /// via `users::list`'s `next_cursor` field.
+    #[must_use]
+    pub fn encode(&self) -> String {
+        format!("{}_{}", self.created_at.to_rfc3339(), self.id.into_inner())
+    }
+
+    /// Decode the wire format. Returns `None` on any parse error — the
+    /// caller treats that as "start of page" rather than 400'ing on a
+    /// stale cursor from a previous schema.
+    #[must_use]
+    pub fn decode(s: &str) -> Option<Self> {
+        let (ts, id) = s.rsplit_once('_')?;
+        let created_at = DateTime::parse_from_rfc3339(ts).ok()?.to_utc();
+        let id = uuid::Uuid::parse_str(id).ok()?;
+        Some(Self {
+            created_at,
+            id: picloud_shared::AppUserId::from(id),
+        })
+    }
+}
+
 #[derive(Debug, Clone, Default)]
 pub struct ListOpts {
-    pub cursor: Option<DateTime<Utc>>,
+    pub cursor: Option<ListCursor>,
     pub limit: i64,
 }
 
 #[derive(Debug, Clone)]
 pub struct ListPage<T> {
     pub items: Vec<T>,
-    pub next_cursor: Option<DateTime<Utc>>,
+    pub next_cursor: Option<ListCursor>,
 }
 
 pub struct PostgresAppUserRepository {
@@ -203,11 +235,13 @@ impl AppUserRepository for PostgresAppUserRepository {
             sqlx::query_as::<_, AppUserRecord>(
                 "SELECT id, app_id, email, display_name, email_verified_at, \
                         last_login_at, created_at, updated_at \
-                 FROM app_users WHERE app_id = $1 AND created_at < $2 \
-                 ORDER BY created_at DESC, id DESC LIMIT $3",
+                 FROM app_users WHERE app_id = $1 \
+                   AND (created_at, id) < ($2, $3) \
+                 ORDER BY created_at DESC, id DESC LIMIT $4",
             )
             .bind(app_id.into_inner())
-            .bind(cursor)
+            .bind(cursor.created_at)
+            .bind(cursor.id.into_inner())
             .bind(limit + 1)
             .fetch_all(&self.pool)
             .await?
@@ -227,7 +261,10 @@ impl AppUserRepository for PostgresAppUserRepository {
         let mut items: Vec<AppUserRow> = rows.into_iter().map(Into::into).collect();
         let next_cursor = if i64::try_from(items.len()).unwrap_or(i64::MAX) > limit {
             let cursor_row = items.pop().expect("len > limit so there is a row");
-            Some(cursor_row.created_at)
+            Some(ListCursor {
+                created_at: cursor_row.created_at,
+                id: cursor_row.id,
+            })
         } else {
             None
         };

crates/manager-core/src/users_admin_api.rs

@@ -19,7 +19,6 @@ use axum::http::StatusCode;
 use axum::response::{IntoResponse, Json, Response};
 use axum::routing::{delete, get, post};
 use axum::{Extension, Router};
-use chrono::{DateTime, Utc};
 use picloud_shared::{
     AppId, AppUser, AppUserId, CreateUserInput, EmailTemplateOpts, Invitation, InvitationId,
     InviteOpts, Principal, UpdateUserInput, UsersError, UsersListOpts, UsersService,
@@ -75,12 +74,14 @@ pub fn app_users_router(state: AppUsersState) -> Router {
 #[derive(Debug, Serialize)]
 pub struct ListUsersResponse {
     pub users: Vec<AppUser>,
-    pub next_cursor: Option<DateTime<Utc>>,
+    /// F-P-012: opaque `<rfc3339>_<uuid>` cursor with id tiebreaker.
+    pub next_cursor: Option<String>,
 }
 
 #[derive(Debug, Deserialize)]
 pub struct ListUsersQuery {
-    pub cursor: Option<DateTime<Utc>>,
+    /// F-P-012: opaque `<rfc3339>_<uuid>` cursor with id tiebreaker.
+    pub cursor: Option<String>,
     pub limit: Option<i64>,
 }
 

crates/manager-core/src/users_service.rs

@@ -560,7 +560,10 @@ impl UsersService for UsersServiceImpl {
             .list(
                 cx.app_id,
                 RepoListOpts {
-                    cursor: opts.cursor,
+                    cursor: opts
+                        .cursor
+                        .as_deref()
+                        .and_then(crate::app_user_repo::ListCursor::decode),
                     limit,
                 },
             )
@@ -584,7 +587,7 @@ impl UsersService for UsersServiceImpl {
             .collect();
         Ok(UsersListPage {
             items,
-            next_cursor: page.next_cursor,
+            next_cursor: page.next_cursor.as_ref().map(|c| c.encode()),
         })
     }