[FR] headless (kimi -p) sessions: ephemeral option + archived-flag support for legacy-schema sessions

Problem

Every non-interactive run of kimi -p "..." creates a persistent session record that shows up in the session sidebar (TUI and web). For users who drive automation through headless runs (CI-ish scripts, cron-style chores, gate verification), the sidebar fills with one-shot sessions titled by their first prompt line, mixed in with real interactive windows. In our workspace 45 honeypot headless runs produced 45 sidebar entries.

What we found

• Print-mode sessions are written with the legacy (v1) session engine: their state.json has no version field and no archived field, while interactive sessions use the v2 schema (version: 2, archived: false). This matches the v1/v2 engine split discussed in #2070.
• Because the native archive mechanism (web Settings -> Archived, 0.23.0+) keys off archived in state.json, it cannot hide these legacy-schema headless sessions even when the field is added manually.
• Verified workaround: kimi -S <session-id> -p "..." reuses an existing session and does NOT create a new sidebar record (session_index.jsonl entry count unchanged). We now route all headless chores through one reused session.

Requests (any subset helps)

1. An ephemeral/no-persist mode for kimi -p (e.g. --no-session / --ephemeral) that skips creating a sidebar-visible session record entirely.
2. Support for the archived flag on legacy-schema (v1/print-mode) sessions, so automation can be hidden from the sidebar like v2 sessions.
3. Optional sidebar grouping/filtering (e.g. hide sessions with no interactive turns, or a per-workspace "automation" bucket), so mixed human/agent usage stays readable.

Environment

• kimi-code 0.29.0, Windows native install
• Repro: run kimi -p "say ok" twice; two new sidebar entries appear. Run kimi -S <id> -p "say ok"; no new entry appears.

Start at the non-interactive kimi -p session-creation path and compare it with reused-session handling via kimi -S. Inspect the legacy and v2 state.json schemas, session_index.jsonl, and the web Settings → Archived behavior. Done should mean implementing and verifying one clearly scoped request: ephemeral persistence, legacy archived support, or sidebar grouping/filtering.