Function newestToolGroup

internal/ctx/ctx.go:242–282

newestToolGroup returns the assistant that issued the newest tool result together with every tool result answering it, chronologically: the minimal well-formed unit that honours "always keep the newest" when the newest history message is a tool result. nil when the newest message isn't an identifiab

(history []Message)

// to a user message. buildMessages always prepends the embedded system prompt as
// wire element 0, so any system message Pack returns is a SECOND, non-leading
// system message, which strict OpenAI-compat backends reject outright ("System
// message must be at the beginning"; observed on strict backends like Ollama
// and llama.cpp), the same class of wire-shape 400 the dangling/orphan/userless passes
// guard against. The only system content reaching history is a soft-nudge note
// (the embedded prompt is never stored there), so demoting to user keeps that note,
// automated-check prefix and all, in front of the model while keeping the wire
// legal everywhere. Must run AFTER anchorUserMessage: a demoted nudge would
// otherwise masquerade as a surviving user message and suppress the original-task
// anchor. Mutates only the copied kept slice, never history.
func demoteSystemMessages(kept []Message) []Message {
	for i := range kept {
		if kept[i].Role == RoleSystem {
			kept[i].Role = RoleUser
		}
	}
	return kept
}

// newestToolGroup returns the assistant that issued the newest tool result
// together with every tool result answering it, chronologically: the minimal
// well-formed unit that honours "always keep the newest" when the newest
// history message is a tool result. nil when the newest message isn't an
// identifiable tool result (the budget walk already keeps non-tool newests) or
// no owning assistant exists (an unpairable tool can't be kept anyway).
func newestToolGroup(history []Message) []Message {
	if len(history) == 0 {
		return nil
	}
	last := history[len(history)-1]
	if last.Role != RoleTool || last.ToolCallID == "" {
		return nil
	}
	owner := -1
search:
	for i := len(history) - 2; i >= 0; i-- {
		if history[i].Role != RoleAssistant {
			continue
		}
		for _, tc := range history[i].ToolCalls {
			if tc.ID == last.ToolCallID {
				owner = i
				break search
			}
		}