diff --git a/pkg/runtime/persistence_observer_bench_test.go b/pkg/runtime/persistence_observer_bench_test.go
new file mode 100644
index 000000000..40f20eb00
--- /dev/null
+++ b/pkg/runtime/persistence_observer_bench_test.go
@@ -0,0 +1,161 @@
+package runtime
+
+import (
+	"context"
+	"database/sql"
+	"sync/atomic"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	_ "modernc.org/sqlite"
+
+	"github.com/docker/docker-agent/pkg/chat"
+	"github.com/docker/docker-agent/pkg/session"
+)
+
+// streamingBenchChunks is the number of AgentChoice deltas exercised per
+// benchmark iteration — roughly the order of magnitude of a long assistant turn.
+const streamingBenchChunks = 500
+
+// countingStore wraps an in-memory store and records AddMessage / UpdateMessage
+// calls so tests can pin the per-chunk persistence contract.
+type countingStore struct {
+	*session.InMemorySessionStore
+	addCalls    atomic.Int64
+	updateCalls atomic.Int64
+}
+
+func newCountingStore() *countingStore {
+	return &countingStore{
+		InMemorySessionStore: session.NewInMemorySessionStore().(*session.InMemorySessionStore),
+	}
+}
+
+func (s *countingStore) AddMessage(ctx context.Context, sessionID string, msg *session.Message) (int64, error) {
+	s.addCalls.Add(1)
+	return s.InMemorySessionStore.AddMessage(ctx, sessionID, msg)
+}
+
+func (s *countingStore) UpdateMessage(ctx context.Context, messageID int64, msg *session.Message) error {
+	s.updateCalls.Add(1)
+	return s.InMemorySessionStore.UpdateMessage(ctx, messageID, msg)
+}
+
+func setupPersistenceObserverBench(tb testing.TB) (*PersistenceObserver, *session.Session, *session.InMemorySessionStore) {
+	tb.Helper()
+	store := session.NewInMemorySessionStore().(*session.InMemorySessionStore)
+	obs := newPersistenceObserver(store)
+	require.NotNil(tb, obs)
+
+	sess := session.New(session.WithID("bench-session"), session.WithUserMessage("hi"))
+	require.NoError(tb, store.AddSession(context.Background(), sess))
+	return obs, sess, store
+}
+
+func emitStreamingChunks(ctx context.Context, obs *PersistenceObserver, sess *session.Session, chunks int) {
+	for range chunks {
+		obs.OnEvent(ctx, sess, AgentChoice("root", sess.ID, "tok"))
+	}
+}
+
+func finalizeStreamingMessage(ctx context.Context, obs *PersistenceObserver, sess *session.Session) {
+	obs.OnEvent(ctx, sess, MessageAdded(sess.ID, &session.Message{
+		AgentName: "root",
+		Message: chat.Message{
+			Role:    chat.MessageRoleAssistant,
+			Content: "done",
+		},
+	}, "root"))
+}
+
+// TestPersistenceObserver_UpdateCountPerChunk documents that each streaming
+// delta triggers a store write: one AddMessage on the first chunk, then one
+// UpdateMessage per subsequent chunk until MessageAddedEvent finalises the row.
+func TestPersistenceObserver_UpdateCountPerChunk(t *testing.T) {
+	t.Parallel()
+
+	const chunks = 100
+	ctx := t.Context()
+
+	store := newCountingStore()
+	obs := newPersistenceObserver(store)
+	require.NotNil(t, obs)
+
+	sess := session.New(session.WithID("s1"), session.WithUserMessage("hi"))
+	require.NoError(t, store.AddSession(ctx, sess))
+
+	emitStreamingChunks(ctx, obs, sess, chunks)
+
+	assert.Equal(t, int64(1), store.addCalls.Load(), "first chunk should INSERT")
+	assert.Equal(t, int64(chunks-1), store.updateCalls.Load(), "each later chunk should UPDATE")
+
+	finalizeStreamingMessage(ctx, obs, sess)
+	// MessageAdded with an existing streaming row issues one more UpdateMessage.
+	assert.Equal(t, int64(chunks), store.updateCalls.Load())
+}
+
+// TestPersistenceObserver_StreamingContentAccumulates verifies mid-stream
+// persistence keeps the growing assistant text in the store.
+func TestPersistenceObserver_StreamingContentAccumulates(t *testing.T) {
+	t.Parallel()
+
+	ctx := t.Context()
+	store := session.NewInMemorySessionStore()
+	obs := newPersistenceObserver(store)
+	require.NotNil(t, obs)
+
+	sess := session.New(session.WithID("s1"), session.WithUserMessage("hi"))
+	require.NoError(t, store.AddSession(ctx, sess))
+
+	obs.OnEvent(ctx, sess, AgentChoice("root", sess.ID, "hel"))
+	obs.OnEvent(ctx, sess, AgentChoice("root", sess.ID, "lo"))
+
+	reloaded, err := store.GetSession(ctx, sess.ID)
+	require.NoError(t, err)
+	require.Len(t, reloaded.Messages, 2) // user + streaming assistant
+	require.NotNil(t, reloaded.Messages[1].Message)
+	assert.Equal(t, "hello", reloaded.Messages[1].Message.Message.Content)
+}
+
+func BenchmarkPersistenceObserver_StreamingChunks(b *testing.B) {
+	ctx := b.Context()
+	obs, sess, _ := setupPersistenceObserverBench(b)
+
+	b.ReportAllocs()
+	b.ResetTimer()
+	for range b.N {
+		emitStreamingChunks(ctx, obs, sess, streamingBenchChunks)
+		finalizeStreamingMessage(ctx, obs, sess)
+	}
+}
+
+func BenchmarkPersistenceObserver_StreamingChunks_SQLite(b *testing.B) {
+	ctx := b.Context()
+	store := openBenchSQLiteStore(b)
+	obs := newPersistenceObserver(store)
+	require.NotNil(b, obs)
+
+	sess := session.New(session.WithID("bench-sqlite"), session.WithUserMessage("hi"))
+	require.NoError(b, store.AddSession(ctx, sess))
+
+	b.ReportAllocs()
+	b.ResetTimer()
+	for range b.N {
+		emitStreamingChunks(ctx, obs, sess, streamingBenchChunks)
+		finalizeStreamingMessage(ctx, obs, sess)
+	}
+}
+
+func openBenchSQLiteStore(b *testing.B) *session.SQLiteSessionStore {
+	b.Helper()
+	db, err := sql.Open("sqlite", ":memory:")
+	require.NoError(b, err)
+	b.Cleanup(func() { _ = db.Close() })
+	db.SetMaxOpenConns(1)
+
+	store, err := session.NewSQLiteSessionStoreFromDB(b.Context(), db)
+	require.NoError(b, err)
+	b.Cleanup(func() { _ = store.Close() })
+	return store
+}