Function prepareMessagesForRequest

coderd/x/chatd/chatloop/chatloop.go:740–784

prepareMessagesForRequest applies the prompt preparation pipeline used immediately before sending messages to a provider. It returns the possibly updated canonical messages and an independent provider-ready prompt. When preparation fails, the prompt result is nil and err is the terminal prompt-prepa

(
	ctx context.Context,
	opts RunOptions,
	messages []fantasy.Message,
	provider string,
	modelName string,
	step int,
	totalSteps int,
)

// prompt. When preparation fails, the prompt result is nil and err is the
// terminal prompt-preparation failure.
func prepareMessagesForRequest(
	ctx context.Context,
	opts RunOptions,
	messages []fantasy.Message,
	provider string,
	modelName string,
	step int,
	totalSteps int,
) (canonical []fantasy.Message, prompt []fantasy.Message, err error) {
	canonical = messages
	if opts.PrepareMessages != nil {
		if updated := opts.PrepareMessages(canonical); updated != nil {
			canonical = updated
		}
	}
	// Copy messages so provider-specific caching mutations don't leak
	// back to the canonical message slice.
	prompt = slices.Clone(canonical)
	prompt, sanitizeStats := chatsanitize.SanitizeAnthropicProviderToolHistory(provider, prompt)
	chatsanitize.LogAnthropicProviderToolSanitization(
		ctx, opts.Logger, "pre_request", provider, modelName, sanitizeStats,
		slog.F("step_index", step),
		slog.F("total_steps", totalSteps),
	)
	prompt, err = chatsanitize.ApplyAnthropicProviderToolGuard(
		ctx, opts.Logger, provider, modelName, prompt,
	)
	if err != nil {
		err = chaterror.WithClassification(
			xerrors.Errorf("apply anthropic provider tool guard: %w", err),
			chaterror.ClassifiedError{
				Message:   "The chat continuation failed due to an internal state mismatch. This is not a configuration or billing issue. Start a new chat to continue.",
				Detail:    "Anthropic replay diagnostic: match=provider_tool_guard_postcondition_failed.",
				Kind:      codersdk.ChatErrorKindGeneric,
				Provider:  provider,
				Retryable: false,
			},
		)
		return canonical, nil, err
	}
	if shouldApplyAnthropicPromptCaching(opts.Model) {
		addAnthropicPromptCaching(prompt)
	}
	return canonical, prompt, nil
}

// guardedAttempt owns an attempt-scoped context and silence guard
// around a provider stream. release is idempotent and frees the