Method compactIfNeeded

pkg/runtime/loop.go:1096–1135

compactIfNeeded estimates the token impact of tool results added since messageCountBefore and triggers proactive compaction when the estimated total exceeds 90% of the context window. This prevents sending an oversized request on the next iteration.

(
	ctx context.Context,
	sess *session.Session,
	a *agent.Agent,
	contextLimit int64,
	messageCountBefore int,
	events EventSink,
)

// total exceeds 90% of the context window. This prevents sending an
// oversized request on the next iteration.
func (r *LocalRuntime) compactIfNeeded(
	ctx context.Context,
	sess *session.Session,
	a *agent.Agent,
	contextLimit int64,
	messageCountBefore int,
	events EventSink,
) {
	// contextLimit is the effective budget (primary window, capped to a smaller
	// dedicated compaction model's window when configured) computed by
	// runStreamLoop, so this site fires consistently with the pre-turn trigger.
	if !r.sessionCompaction || contextLimit <= 0 {
		return
	}

	// Estimate only over the session's own new messages: sub-session
	// content recorded during tool calls (transfer_task and friends)
	// never enters this session's prompt, so counting it here would
	// attribute phantom tokens to a small parent conversation and
	// trigger a compaction that wipes it (see issue #2871).
	newMessages := sess.OwnMessages()[messageCountBefore:]
	var addedTokens int64
	for _, msg := range newMessages {
		addedTokens += compaction.EstimateMessageTokens(&msg.Message)
	}

	if !compaction.ShouldCompact(sess.InputTokens, sess.OutputTokens, addedTokens, contextLimit) {
		return
	}

	slog.InfoContext(ctx, "Proactive compaction: tool results pushed estimated context past 90%% threshold",
		"agent", a.Name(),
		"input_tokens", sess.InputTokens,
		"output_tokens", sess.OutputTokens,
		"added_estimated_tokens", addedTokens,
		"estimated_total", sess.InputTokens+sess.OutputTokens+addedTokens,
		"context_limit", contextLimit,
	)
	r.compactWithReason(ctx, sess, "", compactionReasonThreshold, events)
}

// getTools executes tool retrieval with automatic OAuth handling.
// emitLifecycleEvents controls whether MCPInitStarted/Finished are emitted;