Конвенция для обработки ошибок + рефакторинг кода

internal/httpapi/httpapi_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"database/sql"
 	"encoding/json"
+	"fmt"
 	"io"
 	"log/slog"
 	"net/http"
@@ -14,6 +15,7 @@ import (
 	"git.vakhrushev.me/av/jellybit/internal/httpapi"
 	"git.vakhrushev.me/av/jellybit/internal/ingest"
 	"git.vakhrushev.me/av/jellybit/internal/layout"
+	"git.vakhrushev.me/av/jellybit/internal/magnet"
 	"git.vakhrushev.me/av/jellybit/internal/recognize"
 	"git.vakhrushev.me/av/jellybit/internal/store"
 	"git.vakhrushev.me/av/jellybit/internal/worker"
@@ -104,7 +106,9 @@ func TestAPIAdd(t *testing.T) {
 }
 
 func TestAPIAddBadInput(t *testing.T) {
-	ing := &fakeIngestor{err: ingestErr("bad magnet")}
+	// Источник не magnet → ingest оборачивает magnet.ErrNotMagnet; транспорт
+	// классифицирует это как 400 (некорректный источник).
+	ing := &fakeIngestor{err: fmt.Errorf("ingest: parse source: %w", magnet.ErrNotMagnet)}
 	srv := newServer(t, httpapi.Deps{Ingestor: ing, Commander: &fakeCommander{}, Reader: &fakeReader{}})
 
 	resp, err := http.Post(srv.URL+"/api/downloads", "application/json", strings.NewReader(`{"source":"x"}`))
@@ -156,6 +160,26 @@ func TestAPICancel(t *testing.T) {
 	}
 }
 
+func TestAPICommandConflict(t *testing.T) {
+	// Конфликт состояния (worker.ErrConflict) → 409, не 500.
+	cmd := &fakeCommander{err: fmt.Errorf("cancel: download 5 in wrong state: %w", worker.ErrConflict)}
+	srv := newServer(t, httpapi.Deps{Ingestor: &fakeIngestor{}, Commander: cmd, Reader: &fakeReader{}})
+
+	resp, err := http.Post(srv.URL+"/api/downloads/5/cancel", "", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusConflict {
+		t.Fatalf("status = %d, want 409", resp.StatusCode)
+	}
+	var got map[string]any
+	_ = json.NewDecoder(resp.Body).Decode(&got)
+	if got["download_id"].(float64) != 5 {
+		t.Errorf("download_id корреляции нет: %v", got)
+	}
+}
+
 func TestIndexRenders(t *testing.T) {
 	reader := &fakeReader{list: []store.Download{
 		{ID: 1, SourceType: store.SourceMagnet, SourceRef: "magnet:?xt=urn:btih:abc", State: store.StateDownloading},