diff --git a/internal/session/snapshot.go b/internal/session/snapshot.go
new file mode 100644
index 0000000..e19f064
--- /dev/null
+++ b/internal/session/snapshot.go
@@ -0,0 +1,26 @@
+package session
+
+import (
+	"time"
+
+	"somegit.dev/Owlibou/gnoma/internal/message"
+)
+
+// Metadata holds session summary information persisted alongside messages.
+type Metadata struct {
+	ID           string        `json:"id"`
+	Provider     string        `json:"provider"`
+	Model        string        `json:"model"`
+	TurnCount    int           `json:"turn_count"`
+	Usage        message.Usage `json:"usage"`
+	CreatedAt    time.Time     `json:"created_at"`
+	UpdatedAt    time.Time     `json:"updated_at"`
+	MessageCount int           `json:"message_count"`
+}
+
+// Snapshot is a complete serialisable representation of a session at a point in time.
+type Snapshot struct {
+	ID       string            `json:"id"`
+	Metadata Metadata          `json:"metadata"`
+	Messages []message.Message `json:"messages"`
+}
diff --git a/internal/session/store.go b/internal/session/store.go
new file mode 100644
index 0000000..333c83f
--- /dev/null
+++ b/internal/session/store.go
@@ -0,0 +1,146 @@
+package session
+
+import (
+	"encoding/json"
+	"fmt"
+	"log/slog"
+	"os"
+	"path/filepath"
+	"sort"
+
+	"somegit.dev/Owlibou/gnoma/internal/message"
+)
+
+// SessionStore manages session persistence to .gnoma/sessions/.
+type SessionStore struct {
+	dir     string
+	maxKeep int
+	logger  *slog.Logger
+}
+
+// NewSessionStore creates a store rooted at <projectRoot>/.gnoma/sessions/.
+func NewSessionStore(projectRoot string, maxKeep int, logger *slog.Logger) *SessionStore {
+	return &SessionStore{
+		dir:     filepath.Join(projectRoot, ".gnoma", "sessions"),
+		maxKeep: maxKeep,
+		logger:  logger,
+	}
+}
+
+func (s *SessionStore) Save(snap Snapshot) error {
+	dir := filepath.Join(s.dir, snap.ID)
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		return fmt.Errorf("session %q: create dir: %w", snap.ID, err)
+	}
+
+	if err := atomicWrite(filepath.Join(dir, "metadata.json"), snap.Metadata); err != nil {
+		return fmt.Errorf("session %q: write metadata: %w", snap.ID, err)
+	}
+
+	if err := atomicWrite(filepath.Join(dir, "messages.json"), snap.Messages); err != nil {
+		return fmt.Errorf("session %q: write messages: %w", snap.ID, err)
+	}
+
+	return s.Prune()
+}
+
+func (s *SessionStore) Load(id string) (Snapshot, error) {
+	dir := filepath.Join(s.dir, id)
+
+	metaBytes, err := os.ReadFile(filepath.Join(dir, "metadata.json"))
+	if err != nil {
+		return Snapshot{}, fmt.Errorf("session %q not found: %w", id, err)
+	}
+
+	var meta Metadata
+	if err := json.Unmarshal(metaBytes, &meta); err != nil {
+		return Snapshot{}, fmt.Errorf("session %q: corrupt metadata: %w", id, err)
+	}
+
+	msgBytes, err := os.ReadFile(filepath.Join(dir, "messages.json"))
+	if err != nil {
+		return Snapshot{}, fmt.Errorf("session %q: read messages: %w", id, err)
+	}
+
+	var msgs []message.Message
+	if err := json.Unmarshal(msgBytes, &msgs); err != nil {
+		return Snapshot{}, fmt.Errorf("session %q: corrupt messages: %w", id, err)
+	}
+
+	return Snapshot{
+		ID:       id,
+		Metadata: meta,
+		Messages: msgs,
+	}, nil
+}
+
+func (s *SessionStore) List() ([]Metadata, error) {
+	entries, err := os.ReadDir(s.dir)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, nil
+		}
+		return nil, fmt.Errorf("list sessions: %w", err)
+	}
+
+	var result []Metadata
+	for _, entry := range entries {
+		if !entry.IsDir() {
+			continue
+		}
+		id := entry.Name()
+		metaBytes, err := os.ReadFile(filepath.Join(s.dir, id, "metadata.json"))
+		if err != nil {
+			s.logger.Warn("session: skip unreadable metadata", "id", id, "err", err)
+			continue
+		}
+		var meta Metadata
+		if err := json.Unmarshal(metaBytes, &meta); err != nil {
+			s.logger.Warn("session: skip corrupt metadata", "id", id, "err", err)
+			continue
+		}
+		meta.ID = id
+		result = append(result, meta)
+	}
+
+	sort.Slice(result, func(i, j int) bool {
+		return result[i].UpdatedAt.After(result[j].UpdatedAt)
+	})
+
+	return result, nil
+}
+
+func (s *SessionStore) Prune() error {
+	list, err := s.List()
+	if err != nil {
+		return fmt.Errorf("prune: list sessions: %w", err)
+	}
+
+	if len(list) <= s.maxKeep {
+		return nil
+	}
+
+	for _, meta := range list[s.maxKeep:] {
+		dir := filepath.Join(s.dir, meta.ID)
+		if err := os.RemoveAll(dir); err != nil {
+			s.logger.Warn("session: prune failed", "id", meta.ID, "err", err)
+		}
+	}
+
+	return nil
+}
+
+func atomicWrite(path string, v any) error {
+	data, err := json.Marshal(v)
+	if err != nil {
+		return fmt.Errorf("marshal: %w", err)
+	}
+	tmp := path + ".tmp"
+	if err := os.WriteFile(tmp, data, 0o644); err != nil {
+		return fmt.Errorf("write tmp: %w", err)
+	}
+	if err := os.Rename(tmp, path); err != nil {
+		return fmt.Errorf("rename: %w", err)
+	}
+	return nil
+}
diff --git a/internal/session/store_test.go b/internal/session/store_test.go
new file mode 100644
index 0000000..801b4ae
--- /dev/null
+++ b/internal/session/store_test.go
@@ -0,0 +1,130 @@
+package session_test
+
+import (
+	"fmt"
+	"log/slog"
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+
+	"somegit.dev/Owlibou/gnoma/internal/message"
+	"somegit.dev/Owlibou/gnoma/internal/session"
+)
+
+func makeSnap(id string, updated time.Time) session.Snapshot {
+	return session.Snapshot{
+		ID: id,
+		Metadata: session.Metadata{
+			ID:           id,
+			Provider:     "anthropic",
+			Model:        "claude",
+			TurnCount:    1,
+			UpdatedAt:    updated,
+			CreatedAt:    updated,
+			MessageCount: 2,
+		},
+		Messages: []message.Message{
+			message.NewUserText("hello"),
+			message.NewAssistantText("hi"),
+		},
+	}
+}
+
+func makeStore(t *testing.T) *session.SessionStore {
+	t.Helper()
+	root := t.TempDir()
+	return session.NewSessionStore(root, 3, slog.Default())
+}
+
+func TestSessionStore_SaveLoad(t *testing.T) {
+	store := makeStore(t)
+	snap := makeSnap("sess-001", time.Now().UTC())
+
+	if err := store.Save(snap); err != nil {
+		t.Fatal(err)
+	}
+
+	got, err := store.Load("sess-001")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got.ID != "sess-001" {
+		t.Errorf("ID mismatch: %q", got.ID)
+	}
+	if len(got.Messages) != 2 {
+		t.Errorf("messages: %d", len(got.Messages))
+	}
+	if got.Metadata.Provider != "anthropic" {
+		t.Errorf("provider: %q", got.Metadata.Provider)
+	}
+}
+
+func TestSessionStore_Load_Missing(t *testing.T) {
+	store := makeStore(t)
+	_, err := store.Load("nonexistent")
+	if err == nil {
+		t.Error("expected error for missing session")
+	}
+}
+
+func TestSessionStore_Load_CorruptMetadata(t *testing.T) {
+	root := t.TempDir()
+	store := session.NewSessionStore(root, 3, slog.Default())
+
+	dir := filepath.Join(root, ".gnoma", "sessions", "corrupt-sess")
+	os.MkdirAll(dir, 0o755)
+	os.WriteFile(filepath.Join(dir, "metadata.json"), []byte("not json"), 0o644)
+	os.WriteFile(filepath.Join(dir, "messages.json"), []byte("[]"), 0o644)
+
+	_, err := store.Load("corrupt-sess")
+	if err == nil {
+		t.Error("expected error for corrupt metadata")
+	}
+}
+
+func TestSessionStore_List_SortedByUpdatedAt(t *testing.T) {
+	store := makeStore(t)
+	now := time.Now().UTC()
+
+	store.Save(makeSnap("sess-old", now.Add(-2*time.Hour)))
+	store.Save(makeSnap("sess-new", now))
+	store.Save(makeSnap("sess-mid", now.Add(-1*time.Hour)))
+
+	list, err := store.List()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(list) != 3 {
+		t.Fatalf("expected 3 sessions, got %d", len(list))
+	}
+	if list[0].ID != "sess-new" {
+		t.Errorf("first should be newest: %q", list[0].ID)
+	}
+	if list[2].ID != "sess-old" {
+		t.Errorf("last should be oldest: %q", list[2].ID)
+	}
+}
+
+func TestSessionStore_Prune_RemovesOldest(t *testing.T) {
+	store := makeStore(t) // maxKeep = 3
+	now := time.Now().UTC()
+
+	for i := 0; i < 5; i++ {
+		id := fmt.Sprintf("sess-%03d", i)
+		store.Save(makeSnap(id, now.Add(time.Duration(i)*time.Minute)))
+	}
+
+	list, err := store.List()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(list) != 3 {
+		t.Errorf("expected 3 sessions after prune, got %d", len(list))
+	}
+	for _, m := range list {
+		if m.ID == "sess-000" || m.ID == "sess-001" {
+			t.Errorf("oldest session %q should have been pruned", m.ID)
+		}
+	}
+}