Function anchorUserMessage

internal/ctx/ctx.go:201–213

anchorUserMessage guarantees the packed window carries a user-role message whenever history has one. The newest-first walk drops oldest-first, so a long single turn (one task message, then dozens of assistant+tool rounds that fill the budget) evicts the sole user task and hands the backend a userles

(kept, history []Message)

// path already make. A lone user message carries no tool-call pairing, so this is
// safe after the dangling/orphan passes. No-op when a recent user already
// survived (normal multi-turn) or history has no user message at all.
func anchorUserMessage(kept, history []Message) []Message {
	for _, m := range kept {
		if m.Role == RoleUser {
			return kept
		}
	}
	for i := range history {
		if history[i].Role == RoleUser {
			return append([]Message{history[i]}, kept...)
		}
	}
	return kept
}

// demoteSystemMessages rewrites every system-role message in the packed history