backend: test that no tools loaded omits tools field

Regression guard for tool-free model compatibility: an agent with an
empty tool set must produce requests with no "tools"/"tool_choice"
field. Covers OpenAI, OpenRouter, Ollama, and Anthropic.

cmd/olliesrv/internal/backend/notools_test.go

@@ -0,0 +1,105 @@
+package backend
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"testing"
+)
+
+// These tests lock in the "no tools loaded" compatibility path: an agent with
+// an empty autoLoadTools set (and no /tool_load) produces an empty tool slice,
+// and every backend must then emit a request with NO "tools" field. This keeps
+// Ollie compatible with models that do not support tool/function calling — the
+// answer for such a model is simply to use a tool-free agent.
+
+// captureBody spins up an httptest server, records the raw request body, drains
+// the (empty) stream, and returns the decoded top-level JSON object.
+func captureBody(t *testing.T, build func(baseURL string) (Backend, error)) map[string]json.RawMessage {
+	t.Helper()
+	var rawBody []byte
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		rawBody, _ = io.ReadAll(r.Body)
+		w.Header().Set("Content-Type", "text/event-stream")
+		fmt.Fprint(w, "data: [DONE]\n\n")
+	}))
+	defer srv.Close()
+
+	b, err := build(srv.URL)
+	if err != nil {
+		t.Fatal(err)
+	}
+	msgs := []Message{{Role: "user", Content: "hi"}}
+	// No tools: the empty slice must yield a request without a tools field.
+	ch, err := b.ChatStream(context.Background(), msgs, nil, GenerationParams{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	for range ch { //nolint:revive
+	}
+
+	var top map[string]json.RawMessage
+	json.Unmarshal(rawBody, &top) //nolint:errcheck
+	return top
+}
+
+func assertNoToolsField(t *testing.T, top map[string]json.RawMessage) {
+	t.Helper()
+	if raw, ok := top["tools"]; ok {
+		t.Errorf("request must omit \"tools\" when no tools are loaded; got tools=%s", raw)
+	}
+	if raw, ok := top["tool_choice"]; ok {
+		t.Errorf("request must omit \"tool_choice\" when no tools are loaded; got tool_choice=%s", raw)
+	}
+}
+
+func TestNoTools_OpenAIOmitsToolsField(t *testing.T) {
+	top := captureBody(t, func(baseURL string) (Backend, error) {
+		b, err := NewOpenAI("openai", baseURL, "key")
+		if err != nil {
+			return nil, err
+		}
+		b.SetModel("gpt-4o")
+		return b, nil
+	})
+	assertNoToolsField(t, top)
+}
+
+func TestNoTools_OpenRouterOmitsToolsField(t *testing.T) {
+	top := captureBody(t, func(baseURL string) (Backend, error) {
+		b, err := NewOpenAI("openrouter", baseURL, "key")
+		if err != nil {
+			return nil, err
+		}
+		b.SetModel("mistral-7b")
+		return b, nil
+	})
+	assertNoToolsField(t, top)
+}
+
+func TestNoTools_OllamaOmitsToolsField(t *testing.T) {
+	top := captureBody(t, func(baseURL string) (Backend, error) {
+		return NewOllama(baseURL)
+	})
+	assertNoToolsField(t, top)
+}
+
+func TestNoTools_AnthropicOmitsToolsField(t *testing.T) {
+	top := captureBody(t, func(baseURL string) (Backend, error) {
+		b, err := NewAnthropic("key")
+		if err != nil {
+			return nil, err
+		}
+		u, err := url.Parse(baseURL)
+		if err != nil {
+			return nil, err
+		}
+		b.baseURL = u
+		return b, nil
+	})
+	assertNoToolsField(t, top)
+}