test: completion streaming tests for llamacpp client

Add TestComplete_Streaming (multi-chunk SSE with three tokens) and
TestComplete_HTTPError (400 status propagation) to exercise the
Complete() method alongside the existing chat tests.

Co-Authored-By: Virgil <virgil@lethean.io>
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/llamacpp/client_test.go

@@ -139,3 +139,56 @@ func TestChatComplete_ContextCancelled(t *testing.T) {
 	_ = errFn()
 	assert.Equal(t, []string{"Hello"}, got)
 }
+
+func TestComplete_Streaming(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		assert.Equal(t, "/v1/completions", r.URL.Path)
+		assert.Equal(t, "POST", r.Method)
+		sseLines(w, []string{
+			`{"choices":[{"text":"Once","finish_reason":null}]}`,
+			`{"choices":[{"text":" upon","finish_reason":null}]}`,
+			`{"choices":[{"text":" a time","finish_reason":null}]}`,
+			`{"choices":[{"text":"","finish_reason":"stop"}]}`,
+			"[DONE]",
+		})
+	}))
+	defer ts.Close()
+
+	c := NewClient(ts.URL)
+	tokens, errFn := c.Complete(context.Background(), CompletionRequest{
+		Prompt:      "Once",
+		MaxTokens:   64,
+		Temperature: 0.0,
+		Stream:      true,
+	})
+
+	var got []string
+	for tok := range tokens {
+		got = append(got, tok)
+	}
+	require.NoError(t, errFn())
+	assert.Equal(t, []string{"Once", " upon", " a time"}, got)
+}
+
+func TestComplete_HTTPError(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		http.Error(w, "bad request", http.StatusBadRequest)
+	}))
+	defer ts.Close()
+
+	c := NewClient(ts.URL)
+	tokens, errFn := c.Complete(context.Background(), CompletionRequest{
+		Prompt:      "Hello",
+		Temperature: 0.7,
+		Stream:      true,
+	})
+
+	var got []string
+	for tok := range tokens {
+		got = append(got, tok)
+	}
+	assert.Empty(t, got)
+	err := errFn()
+	require.Error(t, err)
+	assert.Contains(t, err.Error(), "400")
+}