Function TestServer_ForkSession

pkg/server/server_test.go:210–257

TestServer_ForkSession exercises the POST /api/sessions/:id/fork endpoint end-to-end: a fork at the Nth user message must return a new session with the history before that message, a fork-numbered title, and a fresh ID. An out-of-range ordinal must be rejected with 400 Bad Request.

(t *testing.T)

// title, and a fresh ID. An out-of-range ordinal must be rejected with
// 400 Bad Request.
func TestServer_ForkSession(t *testing.T) {
	t.Parallel()

	ctx := t.Context()
	store := session.NewInMemorySessionStore()

	parent := session.New()
	parent.Title = "Original"
	parent.Messages = []session.Item{
		session.NewMessageItem(session.UserMessage("hello")),
		session.NewMessageItem(session.NewAgentMessage("root", &chat.Message{
			Role:    chat.MessageRoleAssistant,
			Content: "hi there",
		})),
		session.NewMessageItem(session.UserMessage("ignore me")),
	}
	require.NoError(t, store.AddSession(ctx, parent))

	lnPath := startServerWithStore(t, ctx, prepareAgentsDir(t), store)

	// Happy path: fork before the second user message (ordinal 1).
	resp := httpDo(t, ctx, http.MethodPost, lnPath,
		"/api/sessions/"+parent.ID+"/fork",
		api.ForkSessionRequest{UserMessageIndex: 1})
	var forked api.SessionResponse
	unmarshal(t, resp, &forked)

	assert.NotEqual(t, parent.ID, forked.ID)
	assert.Equal(t, "Original (fork 1)", forked.Title)
	require.Len(t, forked.Messages, 2)
	assert.Equal(t, "hello", forked.Messages[0].Message.Content)
	assert.Equal(t, "hi there", forked.Messages[1].Message.Content)

	// Fork must be persisted server-side so a subsequent GET returns it.
	getResp := httpGET(t, ctx, lnPath, "/api/sessions/"+forked.ID)
	var fetched api.SessionResponse
	unmarshal(t, getResp, &fetched)
	assert.Equal(t, forked.ID, fetched.ID)
	assert.Equal(t, "Original (fork 1)", fetched.Title)

	// Forking past the last user message (no "full clone" shortcut) must
	// return 400, not 500. This pins the sentinel-driven classification so
	// future error-message reshuffles can't silently flip the status code.
	outOfRange := httpRaw(t, ctx, http.MethodPost, lnPath,
		"/api/sessions/"+parent.ID+"/fork",
		api.ForkSessionRequest{UserMessageIndex: 99})
	assert.Equal(t, http.StatusBadRequest, outOfRange.StatusCode, outOfRange.body)
}

// httpRaw issues an HTTP request and returns the raw response without
// asserting on the status code, so tests can verify 4xx/5xx paths.