The help text for --system-prompt-snapshot now describes the setting as on by default in all cases, rather than only by default for the built-in system prompt (previously, using --system-prompt or --append-system-prompt turned snapshotting off automatically). With the default on, the system prompt - including any text passed via --system-prompt or --append-system-prompt - is rendered once on the conversation's first request, and every later request or resume reuses that exact recorded version, even if a later launch passes different prompt text, until the conversation compacts (summarizes and trims its history).
Relatedly, when snapshotting is on, a set_model system-prompt override now takes effect at the next compaction rather than at the next turn.
This means custom system prompts set via --system-prompt or --append-system-prompt are now also locked in from the first request by default, so changing that text on a later launch of the same conversation won't retroactively change what's already been recorded - only a fresh conversation or a compaction will pick up new text.