Function RenderTranscript

pkg/tools/builtin/sessioncontext/sessioncontext.go:135–185

RenderTranscript renders a previous session as a readable transcript. When the rendered text would exceed maxChars, the oldest messages are dropped (the most recent ones are the most useful for continuing work) and a note records how many were omitted. maxChars <= 0 selects DefaultMaxChars.

(h Header, msgs []chat.Message, maxChars int)

// (the most recent ones are the most useful for continuing work) and a note
// records how many were omitted. maxChars <= 0 selects DefaultMaxChars.
func RenderTranscript(h Header, msgs []chat.Message, maxChars int) string {
	if maxChars <= 0 {
		maxChars = DefaultMaxChars
	}

	var head strings.Builder
	title := strings.TrimSpace(h.Title)
	if title == "" {
		title = "(untitled)"
	}
	fmt.Fprintf(&head, "# Session %s — %s\n", h.ID, title)
	if !h.CreatedAt.IsZero() {
		fmt.Fprintf(&head, "Created: %s\n", h.CreatedAt.Format(time.RFC3339))
	}
	fmt.Fprintf(&head, "Messages: %d\n", h.NumMessages)

	blocks := make([]string, 0, len(msgs))
	for i := range msgs {
		if b := renderMessage(msgs[i]); b != "" {
			blocks = append(blocks, b)
		}
	}

	// Keep the most recent blocks that fit in the remaining budget. The header
	// always stays; the omission note (when needed) is counted against the
	// budget so the final string respects maxChars.
	budget := maxChars - head.Len()
	kept := 0
	used := 0
	for _, b := range slices.Backward(blocks) {
		cost := len(b) + 1 // +1 for the joining newline
		if used+cost > budget && kept > 0 {
			break
		}
		used += cost
		kept++
	}
	omitted := len(blocks) - kept

	var out strings.Builder
	out.WriteString(head.String())
	if omitted > 0 {
		fmt.Fprintf(&out, "\n[%d earlier message(s) omitted to fit the context budget; showing the most recent %d]\n", omitted, kept)
	}
	for _, b := range blocks[len(blocks)-kept:] {
		out.WriteString("\n")
		out.WriteString(b)
		out.WriteString("\n")
	}
	return out.String()
}

// renderMessage turns one chat message into a transcript block, or "" when it
// carries nothing worth showing (e.g. an empty implicit message).