feat: harden support, localize knowledge and add operator availability [skip ci]

Source-only publication of reviewed commit 64e96a7f423673dc29ad56485be9fc79bce8af1c.

Passed in isolation: focused frontend/backend tests, race checks, TypeScript typecheck, lint, Go compilation, Flowgram build, and deterministic SDK build/tests.

Not accepted as a production release: Next.js export/native assembly remains blocked by environment memory limits; browser interaction and MySQL staging acceptance remain unverified. No production server, database/schema, runtime configuration, deployment, release tag, or workflow execution was performed.

Expected source tree: 0a4a7528e9.

internal/handlers/dashboard/knowledge_retrieve_handler_test.go

@@ -0,0 +1,77 @@
+package dashboard
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net/http/httptest"
+	"strings"
+	"testing"
+	"time"
+
+	"agent-desk/internal/pkg/errorsx"
+	"agent-desk/internal/pkg/httpx"
+	"agent-desk/internal/pkg/i18nx"
+
+	"github.com/gin-gonic/gin"
+	"github.com/mlogclub/simple/web"
+)
+
+func TestKnowledgeRequestContextPreservesLocaleAndCancellation(t *testing.T) {
+	parent, cancel := context.WithTimeout(context.Background(), time.Minute)
+	defer cancel()
+	ctx, _ := gin.CreateTestContext(httptest.NewRecorder())
+	ctx.Request = httptest.NewRequest("POST", "/knowledge_retrieve/debug_answer", nil).WithContext(parent)
+	ctx.Request.Header.Set("X-Locale", i18nx.LocaleZhCN)
+	ctx.Request.Header.Set("Accept-Language", i18nx.LocaleZhCN)
+	i18nx.SetLocale(ctx, i18nx.LocaleRuRU)
+	derived := knowledgeRequestContext(ctx)
+	if i18nx.LocaleFromContext(derived) != i18nx.LocaleRuRU {
+		t.Fatal("request locale was lost")
+	}
+	parentDeadline, _ := parent.Deadline()
+	if deadline, ok := derived.Deadline(); !ok || !deadline.Equal(parentDeadline) {
+		t.Fatal("request deadline was lost")
+	}
+	cancel()
+	if !errors.Is(derived.Err(), context.Canceled) {
+		t.Fatal("request cancellation was lost")
+	}
+}
+
+func TestKnowledgeOperationErrorsHideProviderDiagnostics(t *testing.T) {
+	const diagnostic = "synthetic-private-diagnostic"
+	for _, key := range []string{"error.knowledge.indexFailed", "error.knowledge.retrieveFailed"} {
+		for _, cause := range []error{
+			errors.New("SQL failed: " + diagnostic),
+			fmt.Errorf("provider request failed: %w", errors.New(diagnostic)),
+			web.NewError(2000, diagnostic),
+			errorsx.BusinessErrorI18n(0, "error.e0340", diagnostic),
+			errorsx.BusinessErrorI18n(0, "unknown.translation."+diagnostic),
+		} {
+			for _, locale := range []string{i18nx.LocaleEnUS, i18nx.LocaleRuRU, i18nx.LocaleZhCN} {
+				recorder := httptest.NewRecorder()
+				ctx, _ := gin.CreateTestContext(recorder)
+				i18nx.SetLocale(ctx, locale)
+				httpx.WriteJSON(ctx, safeKnowledgeOperationError(cause, key))
+				body := recorder.Body.String()
+				if strings.Contains(body, diagnostic) || !strings.Contains(body, i18nx.Getf(locale, key)) {
+					t.Fatalf("unsafe/unlocalized %s response: %s", key, body)
+				}
+			}
+		}
+	}
+}
+
+func TestKnowledgeOperationErrorPreservesCatalogApplicationError(t *testing.T) {
+	original := errorsx.InvalidParamI18n("error.e0340")
+	wrapped := fmt.Errorf("private provider details: %w", original)
+	if got := safeKnowledgeOperationError(wrapped, "error.knowledge.retrieveFailed"); got != original {
+		t.Fatalf("application error lost: %v", got)
+	}
+	localized := i18nx.Errorf("error.embeddingModel.noneEnabled")
+	got := safeKnowledgeOperationError(fmt.Errorf("private: %w", localized), "error.knowledge.indexFailed")
+	if got.Error() != localized.Error() || strings.Contains(got.Error(), "private") {
+		t.Fatalf("localized application error changed/leaked: %v", got)
+	}
+}