fix(cli): websh ls and exec ls break the --tail contract

[jisung-02]

Background

#330 settles what --tail N means across the CLI: the newest N entries. log, audit, and webftp already behave that way—each passes tail as the limit to api.FetchCursorPages, and the Elasticsearch-backed endpoints sort -date descending, so the first page holds the newest rows.

Two commands break that contract in two different ways.

1. websh ls --tail returns the oldest sessions

cmd/websh/websh_list.go:29-31 fetches every page and then slices the physical end of the list:

if tail > 0 && tail < len(sessionList) {
    sessionList = sessionList[len(sessionList)-tail:]
}

The sessions endpoint sorts newest first (SessionViewSet.ordering = ['-added_at'] in alpacon-server websh/api/views.py:130), so the end of that list is the oldest sessions. alpacon websh ls --tail 5 reports the five oldest sessions while the flag help says "Number of sessions to show".

Fix: slice the head (sessionList[:tail]), since the list is already ordered newest first.

2. exec ls --tail cannot exceed one page

api/event/event.go:213-225 sends page_size=tail in a single request and never looks at ListResponse.Next:

params := map[string]string{}
if pageSize > 0 {
    params["page_size"] = fmt.Sprintf("%d", pageSize)
}
responseBody, err := ac.SendGetRequest(utils.BuildURL(getEventURL, relativePath, params))

The server caps a page at 100 (max_page_size in alpacon-server api/pagination.py), so alpacon exec ls --tail 500 silently returns 100 entries. This is the same defect shape as #330.

Fix: reuse the limit-bounded helper #330 adds to api/pagination.go, so no second page loop is written:

endpoint := path.Join(getEventURL, relativePath)
events, err := api.FetchPagesUpTo[EventDetails](ac, endpoint, nil, tail)

api/event/chunks.go:38 already assembles an endpoint this way before calling api.FetchAllPages, so the shape matches existing code.

Order

Part 2 depends on #330 landing first—it calls the helper that PR introduces. Part 1 is independent and can go first.

References

• cmd/websh/websh_list.go:29-31—tail slice on a descending list
• api/event/event.go:213-225—single request, Next ignored
• api/pagination.go—FetchAllPages, FetchCursorPages
• #330—note ls pagination and the --tail contract