test(session): add JSONLBackend integration tests

8 tests covering the full SessionStore contract through the JSONL
backend: message roundtrip, tool calls, summary, truncation with
compaction, history replacement, empty sessions, session isolation,
and the complete summarization flow (SetSummary → TruncateHistory →
Save).

Includes compile-time interface satisfaction checks for both
SessionManager and JSONLBackend.

Part of #1169

pkg/session/jsonl_backend_test.go

@@ -0,0 +1,179 @@
+package session_test
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/sipeed/picoclaw/pkg/memory"
+	"github.com/sipeed/picoclaw/pkg/providers"
+	"github.com/sipeed/picoclaw/pkg/session"
+)
+
+// Compile-time interface satisfaction checks.
+var (
+	_ session.SessionStore = (*session.SessionManager)(nil)
+	_ session.SessionStore = (*session.JSONLBackend)(nil)
+)
+
+func newBackend(t *testing.T) *session.JSONLBackend {
+	t.Helper()
+	store, err := memory.NewJSONLStore(t.TempDir())
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { store.Close() })
+	return session.NewJSONLBackend(store)
+}
+
+func TestJSONLBackend_AddAndGetHistory(t *testing.T) {
+	b := newBackend(t)
+
+	b.AddMessage("s1", "user", "hello")
+	b.AddMessage("s1", "assistant", "hi")
+
+	history := b.GetHistory("s1")
+	if len(history) != 2 {
+		t.Fatalf("got %d messages, want 2", len(history))
+	}
+	if history[0].Role != "user" || history[0].Content != "hello" {
+		t.Errorf("msg[0] = %+v", history[0])
+	}
+	if history[1].Role != "assistant" || history[1].Content != "hi" {
+		t.Errorf("msg[1] = %+v", history[1])
+	}
+}
+
+func TestJSONLBackend_AddFullMessage(t *testing.T) {
+	b := newBackend(t)
+
+	msg := providers.Message{
+		Role:    "assistant",
+		Content: "done",
+		ToolCalls: []providers.ToolCall{
+			{ID: "tc1", Function: &providers.FunctionCall{Name: "read_file", Arguments: `{"path":"x"}`}},
+		},
+	}
+	b.AddFullMessage("s1", msg)
+
+	history := b.GetHistory("s1")
+	if len(history) != 1 {
+		t.Fatalf("got %d, want 1", len(history))
+	}
+	if len(history[0].ToolCalls) != 1 || history[0].ToolCalls[0].ID != "tc1" {
+		t.Errorf("tool calls = %+v", history[0].ToolCalls)
+	}
+}
+
+func TestJSONLBackend_Summary(t *testing.T) {
+	b := newBackend(t)
+
+	if got := b.GetSummary("s1"); got != "" {
+		t.Errorf("got %q, want empty", got)
+	}
+
+	b.SetSummary("s1", "test summary")
+	if got := b.GetSummary("s1"); got != "test summary" {
+		t.Errorf("got %q, want %q", got, "test summary")
+	}
+}
+
+func TestJSONLBackend_TruncateAndSave(t *testing.T) {
+	b := newBackend(t)
+
+	for i := 0; i < 10; i++ {
+		b.AddMessage("s1", "user", fmt.Sprintf("msg %d", i))
+	}
+	b.TruncateHistory("s1", 3)
+
+	history := b.GetHistory("s1")
+	if len(history) != 3 {
+		t.Fatalf("got %d, want 3", len(history))
+	}
+	if history[0].Content != "msg 7" {
+		t.Errorf("got %q, want %q", history[0].Content, "msg 7")
+	}
+
+	// Save triggers compaction.
+	if err := b.Save("s1"); err != nil {
+		t.Fatal(err)
+	}
+
+	// Messages still accessible after compaction.
+	history = b.GetHistory("s1")
+	if len(history) != 3 {
+		t.Fatalf("after save: got %d, want 3", len(history))
+	}
+}
+
+func TestJSONLBackend_SetHistory(t *testing.T) {
+	b := newBackend(t)
+	b.AddMessage("s1", "user", "old")
+
+	b.SetHistory("s1", []providers.Message{
+		{Role: "user", Content: "new1"},
+		{Role: "assistant", Content: "new2"},
+	})
+
+	history := b.GetHistory("s1")
+	if len(history) != 2 {
+		t.Fatalf("got %d, want 2", len(history))
+	}
+	if history[0].Content != "new1" {
+		t.Errorf("got %q, want %q", history[0].Content, "new1")
+	}
+}
+
+func TestJSONLBackend_EmptySession(t *testing.T) {
+	b := newBackend(t)
+
+	history := b.GetHistory("nonexistent")
+	if history == nil {
+		t.Fatal("got nil, want empty slice")
+	}
+	if len(history) != 0 {
+		t.Errorf("got %d, want 0", len(history))
+	}
+}
+
+func TestJSONLBackend_SessionIsolation(t *testing.T) {
+	b := newBackend(t)
+	b.AddMessage("s1", "user", "session1")
+	b.AddMessage("s2", "user", "session2")
+
+	h1 := b.GetHistory("s1")
+	h2 := b.GetHistory("s2")
+
+	if len(h1) != 1 || h1[0].Content != "session1" {
+		t.Errorf("s1: %+v", h1)
+	}
+	if len(h2) != 1 || h2[0].Content != "session2" {
+		t.Errorf("s2: %+v", h2)
+	}
+}
+
+func TestJSONLBackend_SummarizeFlow(t *testing.T) {
+	// Simulates the real summarization flow in the agent loop:
+	// SetSummary → TruncateHistory → Save
+	b := newBackend(t)
+
+	for i := 0; i < 20; i++ {
+		b.AddMessage("s1", "user", fmt.Sprintf("msg %d", i))
+	}
+
+	b.SetSummary("s1", "conversation about testing")
+	b.TruncateHistory("s1", 4)
+	if err := b.Save("s1"); err != nil {
+		t.Fatal(err)
+	}
+
+	if got := b.GetSummary("s1"); got != "conversation about testing" {
+		t.Errorf("summary = %q", got)
+	}
+	history := b.GetHistory("s1")
+	if len(history) != 4 {
+		t.Fatalf("got %d messages, want 4", len(history))
+	}
+	if history[0].Content != "msg 16" {
+		t.Errorf("first message = %q, want %q", history[0].Content, "msg 16")
+	}
+}