weather: check HTTP status before decoding open-meteo replies (V-589)

Neither CurrentWeather nor geocodeOne checked resp.StatusCode, so a
non-200 forecast reply decoded into a zero-value struct reported as a
real 0-degree answer, and a non-200 geocode reply decoded into an empty
result list and was reported as ErrLocationUnknown — blaming the owner
for a service outage. Both now check http.StatusOK first, matching the
sibling kiwix and websearch clients, and return a wrapped error naming
the status instead.

Adds httptest coverage for a 500 from the forecast endpoint, a 500 from
the geocode endpoint, and a genuine empty geocode result, asserting each
takes a different path.

internal/weather/openmeteo.go

@@ -83,6 +83,9 @@ func (p *OpenMeteoProvider) CurrentWeather(ctx context.Context, location string)
 		return Weather{}, fmt.Errorf("open-meteo: http: %w", err)
 	}
 	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return Weather{}, fmt.Errorf("open-meteo forecast: http %d", resp.StatusCode)
+	}
 
 	body, err := io.ReadAll(resp.Body)
 	if err != nil {
@@ -192,6 +195,9 @@ func (p *OpenMeteoProvider) geocodeOne(ctx context.Context, location string) (la
 		return 0, 0, "", err
 	}
 	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return 0, 0, "", fmt.Errorf("open-meteo geocode: http %d", resp.StatusCode)
+	}
 
 	body, err := io.ReadAll(resp.Body)
 	if err != nil {

internal/weather/openmeteo_test.go

@@ -3,9 +3,11 @@ package weather
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"net/http"
 	"net/http/httptest"
+	"strings"
 	"testing"
 )
 
@@ -76,6 +78,87 @@ func (t *mockTransport) RoundTrip(r *http.Request) (*http.Response, error) {
 	return http.DefaultTransport.RoundTrip(req)
 }
 
+// TestOpenMeteoProvider_ForecastHTTPError — a non-200 forecast reply must not
+// decode into a zero-value Weather{Temperature: 0, Condition: "неизвестно"}
+// reported as success (Vikunja #589). It must be a distinct error, not
+// ErrLocationUnknown, so the caller does not blame the owner's city.
+func TestOpenMeteoProvider_ForecastHTTPError(t *testing.T) {
+	mock := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path == "/v1/search" {
+			json.NewEncoder(w).Encode(geoResponse{
+				Results: []geoResult{{Name: "Moscow", Latitude: 55.7558, Longitude: 37.6173, Country: "Russia"}},
+			})
+			return
+		}
+		w.WriteHeader(http.StatusInternalServerError)
+	}))
+	defer mock.Close()
+
+	p := NewOpenMeteoProvider()
+	p.SetClient(&http.Client{Transport: &mockTransport{
+		geoURL:      mock.URL + "/v1/search",
+		forecastURL: mock.URL + "/v1/forecast",
+	}})
+
+	w, err := p.CurrentWeather(context.Background(), "Moscow")
+	if err == nil {
+		t.Fatalf("CurrentWeather: want error, got Weather{%+v}", w)
+	}
+	if errors.Is(err, ErrLocationUnknown) {
+		t.Fatalf("CurrentWeather: want a service error, got ErrLocationUnknown: %v", err)
+	}
+	if !strings.Contains(err.Error(), "500") {
+		t.Errorf("CurrentWeather: error %q does not name the status", err.Error())
+	}
+}
+
+// TestOpenMeteoProvider_GeocodeHTTPError — a non-200 geocode reply must not be
+// read as "no such city" (ErrLocationUnknown). A 500 is a service outage, and
+// the owner hears a different sentence for each (Vikunja #589).
+func TestOpenMeteoProvider_GeocodeHTTPError(t *testing.T) {
+	mock := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusInternalServerError)
+	}))
+	defer mock.Close()
+
+	p := NewOpenMeteoProvider()
+	p.SetClient(&http.Client{Transport: &mockTransport{
+		geoURL:      mock.URL + "/v1/search",
+		forecastURL: mock.URL + "/v1/forecast",
+	}})
+
+	_, err := p.CurrentWeather(context.Background(), "Уфе")
+	if err == nil {
+		t.Fatal("CurrentWeather: want error")
+	}
+	if errors.Is(err, ErrLocationUnknown) {
+		t.Fatalf("CurrentWeather: want a service error, got ErrLocationUnknown: %v", err)
+	}
+	if !strings.Contains(err.Error(), "500") {
+		t.Errorf("CurrentWeather: error %q does not name the status", err.Error())
+	}
+}
+
+// TestOpenMeteoProvider_GeocodeEmptyResult — a genuine 200 reply with no
+// results is still ErrLocationUnknown, distinct from a service failure.
+func TestOpenMeteoProvider_GeocodeEmptyResult(t *testing.T) {
+	mock := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		json.NewEncoder(w).Encode(geoResponse{Results: nil})
+	}))
+	defer mock.Close()
+
+	p := NewOpenMeteoProvider()
+	p.SetClient(&http.Client{Transport: &mockTransport{
+		geoURL:      mock.URL + "/v1/search",
+		forecastURL: mock.URL + "/v1/forecast",
+	}})
+
+	_, err := p.CurrentWeather(context.Background(), "Атлантида")
+	if !errors.Is(err, ErrLocationUnknown) {
+		t.Fatalf("CurrentWeather: want ErrLocationUnknown, got %v", err)
+	}
+}
+
 func TestStubProvider(t *testing.T) {
 	p := NewStubProvider()
 	_, err := p.CurrentWeather(context.Background(), "Moscow")