implement /compact and /clear commands

- /compact: summarizes evicted context messages via LLM call, replaces
  them with a single summary system message
- /clear: resets session and display
- ContextBuilder.EvictedMessages(): returns messages outside bounded window
- Session.Compact(): drives the summarization and history replacement

agent/context.go

@@ -96,6 +96,36 @@ func (cb *ContextBuilder) Truncate(i int) {
 	}
 }
 
+// EvictedMessages returns the messages that would be dropped by buildBounded.
+func (cb *ContextBuilder) EvictedMessages() []backend.Message {
+	var rest []backend.Message
+	for _, m := range cb.messages {
+		if m.Role != "system" {
+			rest = append(rest, m)
+		}
+	}
+	ts := computeTailStart(rest, cb.cfg.TailMessages)
+	older := rest[:ts]
+
+	used := cb.cfg.FixedOverheadChars + msgSliceChars(cb.messages) - msgSliceChars(older)
+	budget := cb.cfg.SoftLimit - used
+
+	var included []backend.Message
+	for i := len(older) - 1; i >= 0; i-- {
+		size := msgChars(older[i])
+		if budget-size < 0 {
+			break
+		}
+		budget -= size
+		included = append(included, older[i])
+	}
+	evictCount := len(older) - len(included)
+	if evictCount == 0 {
+		return nil
+	}
+	return older[:evictCount]
+}
+
 // BoundedHistory returns a context-window-safe slice of messages.
 func (cb *ContextBuilder) BoundedHistory() []backend.Message {
 	return cb.buildBounded(false)

agent/session.go

@@ -1,6 +1,12 @@
 package agent
 
-import "ollie/backend"
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	"ollie/backend"
+)
 
 // Session is an ephemeral in-memory state backend.
 // It lives only for the duration of the process; nothing is persisted.
@@ -57,6 +63,53 @@ func (s *Session) MarkComplete() error {
 	return nil
 }
 
+// Compact summarizes messages outside the bounded window via an LLM call,
+// replacing them with a single summary system message.
+// Returns the number of messages replaced, or 0 if nothing to compact.
+func (s *Session) Compact(ctx context.Context, b backend.Backend, model string) (int, error) {
+	evicted := s.ctx.EvictedMessages()
+	if len(evicted) == 0 {
+		return 0, nil
+	}
+
+	// Build a prompt asking the model to summarize the evicted messages.
+	var sb strings.Builder
+	for _, m := range evicted {
+		fmt.Fprintf(&sb, "%s: %s\n", m.Role, m.Content)
+	}
+	prompt := "Summarize the following conversation history concisely, preserving key facts, decisions, and context:\n\n" + sb.String()
+
+	ch, err := b.ChatStream(ctx, model, []backend.Message{
+		{Role: "user", Content: prompt},
+	}, nil)
+	if err != nil {
+		return 0, fmt.Errorf("compact: %w", err)
+	}
+
+	var summary strings.Builder
+	for ev := range ch {
+		if ev.Content != "" {
+			summary.WriteString(ev.Content)
+		}
+		if ev.Done {
+			break
+		}
+	}
+
+	// Replace evicted messages with summary.
+	all := s.ctx.Messages()
+	s.ctx.Truncate(0)
+	s.ctx.Append(backend.Message{
+		Role:    "system",
+		Content: "[conversation summary: " + strings.TrimSpace(summary.String()) + "]",
+	})
+	// Re-append the non-evicted messages.
+	for _, m := range all[len(evicted):] {
+		s.ctx.Append(m)
+	}
+	return len(evicted), nil
+}
+
 // Rollback removes any trailing non-user messages from history, discarding
 // an incomplete assistant turn caused by an interruption.
 func (s *Session) Rollback() {

main.go

@@ -854,6 +854,21 @@ func (m *model) handleCommand(input string) bool {
 		m.display = append(m.display, fmt.Sprintf("agent: %s", name))
 		return true
 
+	case "/compact":
+		if m.session == nil {
+			m.display = append(m.display, "nothing to compact")
+			return true
+		}
+		n, err := m.session.Compact(context.Background(), m.loopcfg.Backend, m.loopcfg.Model)
+		if err != nil {
+			m.display = append(m.display, "compact error: "+err.Error())
+		} else if n == 0 {
+			m.display = append(m.display, "nothing to compact")
+		} else {
+			m.display = append(m.display, fmt.Sprintf("compacted %d messages", n))
+		}
+		return true
+
 	case "/clear":
 		m.session = nil
 		m.display = nil
@@ -865,6 +880,7 @@ func (m *model) handleCommand(input string) bool {
 		m.display = append(m.display, "  /agent [name]    - Show or switch active agent")
 		m.display = append(m.display, "  /backend <type>  - Switch backend (ollama, openai)")
 		m.display = append(m.display, "  /model <name>    - Switch model")
+		m.display = append(m.display, "  /compact         - Summarize evicted context messages")
 		m.display = append(m.display, "  /clear           - Clear session and display")
 		m.display = append(m.display, "  /help            - Show this help")
 		return true