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/ai/rag/faq_content.go

@@ -0,0 +1,82 @@
+package rag
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"strings"
+
+	"agent-desk/internal/models"
+	"agent-desk/internal/pkg/i18nx"
+)
+
+// faqContent keeps application-owned labels separate from source text. Never
+// translate, trim, or replace substrings in the source question or answer.
+type faqContent struct {
+	question         string
+	similarQuestions []string
+	answer           string
+}
+
+func sourceFAQContent(faq models.KnowledgeFAQ) faqContent {
+	content := faqContent{question: faq.Question, answer: faq.Answer}
+	if faq.SimilarQuestions != "" {
+		_ = json.Unmarshal([]byte(faq.SimilarQuestions), &content.similarQuestions)
+	}
+	return content
+}
+
+func (content faqContent) render(locale string) string {
+	parts := []string{i18nx.Getf(locale, "knowledge.rag.faq.question", content.question)}
+	if len(content.similarQuestions) > 0 {
+		similar := joinNonEmptySimilarQuestions(content.similarQuestions, i18nx.Getf(locale, "knowledge.rag.faq.separator"))
+		parts = append(parts, i18nx.Getf(locale, "knowledge.rag.faq.similarQuestions", similar))
+	}
+	parts = append(parts, i18nx.Getf(locale, "knowledge.rag.faq.answer", content.answer))
+	return strings.Join(parts, "\n")
+}
+
+// Index generation deliberately uses the configured default, not the locale of
+// whichever administrator requested a build. A locale read never re-embeds data.
+func buildFAQChunkContent(faq models.KnowledgeFAQ) string {
+	return sourceFAQContent(faq).render(i18nx.DefaultLocale)
+}
+
+// legacyChinese renders the exact pre-localization serialization. This is a
+// recognition format, not UI copy. Keep it frozen when catalog wording changes.
+func (content faqContent) legacyChinese() string {
+	parts := []string{fmt.Sprintf("问题：%s", content.question)}
+	if len(content.similarQuestions) > 0 {
+		parts = append(parts, "相似问："+joinNonEmptySimilarQuestions(content.similarQuestions, "；"))
+	}
+	parts = append(parts, "回答："+content.answer)
+	return strings.Join(parts, "\n")
+}
+
+// Only a full byte-for-byte match against a generated representation of the
+// current source proves which text belongs to us. Stale/manual/malformed chunks
+// stay as recorded. In particular, do not infer labels by splitting on Chinese
+// words: the source content may itself contain those words or arbitrary lines.
+// This function is for live retrieval only, never historical log replay.
+func renderVerifiedFAQChunkContent(ctx context.Context, stored string, faq models.KnowledgeFAQ) string {
+	content := sourceFAQContent(faq)
+	if stored == content.legacyChinese() {
+		return content.render(i18nx.LocaleFromContext(ctx))
+	}
+	for _, locale := range []string{i18nx.LocaleEnUS, i18nx.LocaleRuRU, i18nx.LocaleZhCN} {
+		if stored == content.render(locale) {
+			return content.render(i18nx.LocaleFromContext(ctx))
+		}
+	}
+	return stored
+}
+
+func joinNonEmptySimilarQuestions(items []string, separator string) string {
+	nonEmpty := make([]string, 0, len(items))
+	for _, item := range items {
+		if item != "" {
+			nonEmpty = append(nonEmpty, item)
+		}
+	}
+	return strings.Join(nonEmpty, separator)
+}