diff --git a/.ai-specs/PROJECT_CONTEXT.md b/.ai-specs/PROJECT_CONTEXT.md
index d558f56..be4491b 100644
--- a/.ai-specs/PROJECT_CONTEXT.md
+++ b/.ai-specs/PROJECT_CONTEXT.md
@@ -16,6 +16,19 @@
 - **Bundle system**: menaion-bundles, lives bundles (month-prefixed + misc split), service templates
 - **File routing**: CIds with `01`-`12` prefix → month files, else `misc/{first-digit}.json`
 
+### Language Model (UI vs. Content)
+- **UI strings**: en/ru/cu via `getTranslations()`; completeness checked by `validate-i18n.ts`
+- **Service language** (`serviceLang` in `service-view.ts`): `en → en`, `cu → cu`, **`ru → cu`** —
+  a Russian interface intentionally renders services in Church Slavonic
+- **Service content fallback chain**: `serviceLang → cu → shared` (texts, prayers, headers,
+  lives, octoechos, templates); `ru/services/` carries only `var/`
+- **Scripture inside services** follows the service language: en → `en/bible/kjv`,
+  cu (and ru) → `cu/bible/elis`
+- **Bible reader tab** is independent: 13 translations (incl. `ru/bible/synod`), any UI language
+- **Fonts**: the Slavonic font setting applies to liturgical text for cu **and** ru
+  (`getFontClass()`)
+- **Calendar authority**: `cu/menaion-bundle.json`; `{lang}-menaion-bundle.json` overrides
+
 ### Core Scripts
 - `convert-services.ts` — Service XML to JSON conversion
 - `enrich-lives.ts` — Fuzzy matching and enrichment pipeline (Chetyi-Minei + Bulgakov)
@@ -44,6 +57,9 @@
 - **Bundle CIds must exist**: Menaion CIds require corresponding lives entries
 - **Static data is tracked**: `static/data/` in git (except `scripts/output/minei.json`)
 - **Validation must pass**: Changes must pass `tsc --noEmit`, `npm run build`
+- **Content policies**: service/Bible texts are sourced (never translated), cu text is
+  verbatim (no normalisation/latinisation), service assembly follows the Typicon — see
+  `.ai-specs/WORKING_POLICIES.md` ("Liturgical Content Policies")
 
 ## Key Script Quick Reference
 
diff --git a/.ai-specs/WORKING_POLICIES.md b/.ai-specs/WORKING_POLICIES.md
index bc6ba6e..ff4e8cb 100644
--- a/.ai-specs/WORKING_POLICIES.md
+++ b/.ai-specs/WORKING_POLICIES.md
@@ -16,6 +16,27 @@
 - **Forbidden**: Deleting or renaming CIds without proper validation
 - **Forbidden**: Changing JSON structure without updating related code
 
+## Liturgical Content Policies
+
+### Never Translate Service or Bible Texts
+- All liturgical and scriptural texts must be **sourced** through the data pipeline
+  (original-language conversions, Chetyi-Minei, Bulgakov, EPUB/PDF imports, etc.)
+- Never machine-translate, paraphrase or invent text — not even "just one line"
+- Missing text stays empty (the app falls back `serviceLang → cu → shared`) until its
+  source is converted
+
+### Church Slavonic Texts Are Presented Verbatim
+- Never "normalise", latinise, transliterate or strip diacritics/accents/titla from cu texts
+- Render the text exactly as stored in the source data; display-layer transformations
+  are forbidden
+- Orthography fixes belong in the conversion pipeline and must preserve the source
+
+### Service Assembly Follows the Typicon
+- Service-building logic (templates, ordering, conditional rules, canons) must reproduce
+  the Typicon
+- Whenever service building logic is changed, check the expected structure against the
+  Typicon (and the pinned service data) before and after the change
+
 ## Validation Requirements
 
 ### Pre-Commit Checklist
diff --git a/DATA_EN.md b/DATA_EN.md
index ae70fe4..2a348ab 100644
--- a/DATA_EN.md
+++ b/DATA_EN.md
@@ -51,8 +51,8 @@ static/data/
 │   ├── menaion/                     # Daily menaion entries (366 days)
 │   ├── calendar/                    # Calendar metadata
 │   └── services/                    # Service templates
-├── cu/                              # Church Slavonic (similar structure)
-├── ru/                              # Russian (lives, services)
+├── cu/                              # Church Slavonic (authoritative calendar + service texts)
+├── ru/                              # Russian (enriched lives; services fall back to cu)
 ├── el/                              # Greek (includes mono/)
 ├── fr/                              # French
 ├── zh/                              # Chinese (includes Hans/, Hant/)
diff --git a/DATA_RUS.md b/DATA_RUS.md
index 8765664..3509050 100644
--- a/DATA_RUS.md
+++ b/DATA_RUS.md
@@ -51,8 +51,8 @@ static/data/
 │   ├── menaion/                     # Ежедневные записи минеи (366 дней)
 │   ├── calendar/                    # Метаданные календаря
 │   └── services/                    # Шаблоны богослужений
-├── cu/                              # Церковнославянский (аналогичная структура)
-├── ru/                              # Русский (жития, богослужения)
+├── cu/                              # Церковнославянский (авторитетный календарь и богослужебные тексты)
+├── ru/                              # Русский (обогащённые жития; богослужения берутся из cu)
 ├── el/                              # Греческий (включает mono/)
 ├── fr/                              # Французский
 ├── zh/                              # Китайский (включает Hans/, Hant/)