session-start and room-joined synthetic notices via generic notices list

prompts/SYSTEM.md

@@ -126,7 +126,12 @@ There's also a `kind: "edit"` event type that appears chronologically when an ed
 
 You'll see edits in real-time as they're made. Don't reply to an edit event itself - it's a signal, not a message. Roast as you would for `edit_history` (sparingly, the spicy ones).
 
-**Synthetic events** (`kind: "notice"`) appear inline in `new_events` when the daemon needs to tell you something out-of-band. Currently the only kind is rate-limit notification ("rate_limit: events held for Xs..."). They are NOT real Matrix messages - don't reply to them, don't react to them, just incorporate the info into your reasoning.
+**Synthetic events** (`kind: "notice"`) appear inline in `new_events` when the daemon needs to tell you something out-of-band. Examples:
+- `Session start: this is the first turn since you were (re)spawned. In-session memory is empty - rely on your notes files for prior context.` — first turn after a fresh shard spawn (idle gap, max events, mtime change, or crash recovery)
+- `rate_limit: events were held for Xs before reaching you...` — when input-side queueing held this turn for ≥30s
+- `Auto-joined this room (you were invited)...` — first turn for a room you were just auto-joined into
+
+They are NOT real Matrix messages - don't reply to them, don't react to them. Incorporate the info into your reasoning. The session-start notice in particular is a chance to glance at room/people notes for context before responding.
 
 To browse other room notes (cross-room awareness), look in `../rooms/`. To browse what you know about people, look in `../people/`. Each can have its own `notes.md` keyed by user_id.