feat: session lifecycle wrapper with manifest capture and session logging

Refactor new/resume/open to use session.Run() which wraps child process launch with pre/post manifest capture and append-only session logging to logs/sessions.log. Bump version to 0.2.0.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/session/log.go

@@ -0,0 +1,122 @@
+package session
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+	"time"
+)
+
+// SessionInfo holds data for a session log entry.
+type SessionInfo struct {
+	Agent     string
+	Mode      string
+	StartTime time.Time
+	EndTime   time.Time
+	Diff      *ManifestDiff
+}
+
+// FormatDuration returns a human-readable duration string like "1h 14m 48s".
+func FormatDuration(d time.Duration) string {
+	h := int(d.Hours())
+	m := int(d.Minutes()) % 60
+	s := int(d.Seconds()) % 60
+
+	if h > 0 {
+		return fmt.Sprintf("%dh %dm %ds", h, m, s)
+	}
+	if m > 0 {
+		return fmt.Sprintf("%dm %ds", m, s)
+	}
+	return fmt.Sprintf("%ds", s)
+}
+
+// FormatSessionEntry formats a session log entry as a human-readable string.
+func FormatSessionEntry(info *SessionInfo) string {
+	var b strings.Builder
+
+	duration := info.EndTime.Sub(info.StartTime)
+	timeFmt := "2006-01-02 15:04:05"
+
+	fmt.Fprintf(&b, "── Session %s ──\n", info.StartTime.Format(timeFmt))
+	fmt.Fprintf(&b, "Agent:    %s\n", info.Agent)
+	fmt.Fprintf(&b, "Mode:     %s\n", info.Mode)
+	fmt.Fprintf(&b, "Start:    %s\n", info.StartTime.Format(timeFmt))
+	fmt.Fprintf(&b, "End:      %s\n", info.EndTime.Format(timeFmt))
+	fmt.Fprintf(&b, "Duration: %s\n", FormatDuration(duration))
+
+	b.WriteString("\nAdded:\n")
+	if len(info.Diff.Added) > 0 {
+		sorted := make([]string, len(info.Diff.Added))
+		copy(sorted, info.Diff.Added)
+		sort.Strings(sorted)
+		for _, f := range sorted {
+			fmt.Fprintf(&b, "  %s\n", f)
+		}
+	} else {
+		b.WriteString("  (none)\n")
+	}
+
+	b.WriteString("\nModified:\n")
+	if len(info.Diff.Modified) > 0 {
+		sorted := make([]string, len(info.Diff.Modified))
+		copy(sorted, info.Diff.Modified)
+		sort.Strings(sorted)
+		for _, f := range sorted {
+			fmt.Fprintf(&b, "  %s\n", f)
+		}
+	} else {
+		b.WriteString("  (none)\n")
+	}
+
+	b.WriteString("\nDeleted:\n")
+	if len(info.Diff.Deleted) > 0 {
+		sorted := make([]string, len(info.Diff.Deleted))
+		copy(sorted, info.Diff.Deleted)
+		sort.Strings(sorted)
+		for _, f := range sorted {
+			fmt.Fprintf(&b, "  %s\n", f)
+		}
+	} else {
+		b.WriteString("  (none)\n")
+	}
+
+	notesChanged := NotesUpdated(info.Diff)
+	if notesChanged {
+		b.WriteString("\nNotes updated: yes\n")
+	} else {
+		b.WriteString("\nNotes updated: no\n")
+	}
+
+	// Short session with no changes note
+	noChanges := len(info.Diff.Added) == 0 && len(info.Diff.Modified) == 0 && len(info.Diff.Deleted) == 0
+	if duration < 5*time.Second && noChanges {
+		b.WriteString("(No changes detected)\n")
+	}
+
+	b.WriteString("────────────────────────────────\n")
+
+	return b.String()
+}
+
+// AppendSessionLog appends a session entry to logs/sessions.log.
+func AppendSessionLog(wsDir string, info *SessionInfo) error {
+	logDir := filepath.Join(wsDir, "logs")
+	if err := os.MkdirAll(logDir, 0755); err != nil {
+		return err
+	}
+
+	logPath := filepath.Join(logDir, "sessions.log")
+	entry := FormatSessionEntry(info)
+
+	f, err := os.OpenFile(logPath, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	_, err = f.WriteString("\n" + entry)
+	return err
+}