feat: info page tab replacement — replaces_tab field + API

- Add replaces_tab column to InfoPage ('faq','rules','privacy','offer')
- Migration 0067: add nullable replaces_tab column
- CRUD: clear_replaces_tab ensures one page per tab, get_tab_replacements
  returns {tab: slug} mapping for active pages
- Admin routes: auto-clear old assignment on create/update
- Public route: GET /info-pages/tab-replacements (no auth)
- Schemas: replaces_tab with regex validation in all request/response models

app/cabinet/routes/admin_info_pages.py

@@ -6,6 +6,7 @@ from sqlalchemy.exc import IntegrityError
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.database.crud.info_pages import (
+    clear_replaces_tab,
     create_info_page,
     delete_info_page,
     get_all_info_pages,
@@ -74,6 +75,9 @@ async def create_page(
 ) -> InfoPageResponse:
     """Create a new info page."""
     try:
+        if request.replaces_tab:
+            await clear_replaces_tab(db, request.replaces_tab)
+
         page = await create_info_page(
             db,
             slug=request.slug,
@@ -83,6 +87,7 @@ async def create_page(
             is_active=request.is_active,
             sort_order=request.sort_order,
             icon=request.icon,
+            replaces_tab=request.replaces_tab,
         )
     except IntegrityError:
         raise HTTPException(
@@ -116,6 +121,11 @@ async def update_page(
 
     try:
         update_data = request.model_dump(exclude_unset=True)
+
+        replaces_tab = update_data.get('replaces_tab')
+        if replaces_tab is not None:
+            await clear_replaces_tab(db, replaces_tab, exclude_page_id=page_id)
+
         page = await update_info_page(db, page_id, **update_data)
     except IntegrityError:
         raise HTTPException(

app/cabinet/routes/info_pages.py

@@ -4,7 +4,7 @@ import structlog
 from fastapi import APIRouter, Depends, HTTPException, Path, Query, status
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from app.database.crud.info_pages import get_all_info_pages, get_info_page_by_slug
+from app.database.crud.info_pages import get_all_info_pages, get_info_page_by_slug, get_tab_replacements
 
 from ..dependencies import get_cabinet_db
 from ..schemas.info_pages import InfoPageListItem, InfoPageResponse
@@ -32,6 +32,25 @@ async def list_active_info_pages(
         )
 
 
+@router.get('/tab-replacements')
+async def get_info_page_tab_replacements(
+    db: AsyncSession = Depends(get_cabinet_db),
+) -> dict[str, str | None]:
+    """Get tab replacement mapping (public, no auth required).
+
+    Returns a dict mapping each replaceable tab to the info page slug that replaces it,
+    or null if no replacement is set: ``{faq: slug_or_null, ...}``.
+    """
+    try:
+        return await get_tab_replacements(db)
+    except Exception:
+        logger.exception('Failed to get tab replacements')
+        raise HTTPException(
+            status_code=status.HTTP_500_INTERNAL_SERVER_ERROR,
+            detail='Failed to load tab replacements',
+        )
+
+
 @router.get('/{slug}', response_model=InfoPageResponse)
 async def get_info_page_by_slug_public(
     slug: str = Path(..., max_length=200, pattern=r'^[a-z0-9\-]+$'),

app/cabinet/schemas/info_pages.py

@@ -16,6 +16,7 @@ class InfoPageResponse(BaseModel):
     is_active: bool
     sort_order: int
     icon: str | None = None
+    replaces_tab: str | None = None
     created_at: datetime
     updated_at: datetime | None = None
 
@@ -32,6 +33,7 @@ class InfoPageListItem(BaseModel):
     is_active: bool
     sort_order: int
     icon: str | None = None
+    replaces_tab: str | None = None
     updated_at: datetime | None = None
 
     model_config = ConfigDict(from_attributes=True)
@@ -47,6 +49,7 @@ class InfoPageCreateRequest(BaseModel):
     is_active: bool = True
     sort_order: int = 0
     icon: str | None = Field(None, max_length=50)
+    replaces_tab: str | None = Field(None, pattern=r'^(faq|rules|privacy|offer)$')
 
 
 class InfoPageUpdateRequest(BaseModel):
@@ -59,6 +62,7 @@ class InfoPageUpdateRequest(BaseModel):
     is_active: bool | None = None
     sort_order: int | None = None
     icon: str | None = Field(None, max_length=50)
+    replaces_tab: str | None = Field(None, pattern=r'^(faq|rules|privacy|offer)$')
 
 
 class ReorderItem(BaseModel):

app/database/crud/info_pages.py

@@ -23,6 +23,7 @@ _ALLOWED_UPDATE_FIELDS: frozenset[str] = frozenset(
         'is_active',
         'sort_order',
         'icon',
+        'replaces_tab',
     }
 )
 
@@ -30,6 +31,7 @@ _ALLOWED_UPDATE_FIELDS: frozenset[str] = frozenset(
 _NULLABLE_UPDATE_FIELDS: frozenset[str] = frozenset(
     {
         'icon',
+        'replaces_tab',
     }
 )
 
@@ -44,6 +46,7 @@ async def create_info_page(
     is_active: bool = True,
     sort_order: int = 0,
     icon: str | None = None,
+    replaces_tab: str | None = None,
 ) -> InfoPage:
     """Create a new info page.
 
@@ -58,6 +61,7 @@ async def create_info_page(
         is_active=is_active,
         sort_order=sort_order,
         icon=icon,
+        replaces_tab=replaces_tab,
     )
 
     db.add(page)
@@ -150,6 +154,48 @@ async def delete_info_page(db: AsyncSession, page_id: int) -> None:
     logger.info('Deleted info page', page_id=page_id)
 
 
+async def get_tab_replacements(db: AsyncSession) -> dict[str, str | None]:
+    """Return a mapping of tab name to info page slug for active pages with replaces_tab set.
+
+    Returns dict like ``{'faq': 'my-custom-faq', 'rules': None, 'privacy': None, 'offer': None}``.
+    """
+    result_map: dict[str, str | None] = {
+        'faq': None,
+        'rules': None,
+        'privacy': None,
+        'offer': None,
+    }
+
+    stmt = select(InfoPage).where(
+        InfoPage.is_active.is_(True),
+        InfoPage.replaces_tab.isnot(None),
+    )
+    result = await db.execute(stmt)
+    for page in result.scalars().all():
+        if page.replaces_tab in result_map:
+            result_map[page.replaces_tab] = page.slug
+
+    return result_map
+
+
+async def clear_replaces_tab(db: AsyncSession, tab: str, *, exclude_page_id: int | None = None) -> None:
+    """Clear replaces_tab for all pages that currently replace the given tab.
+
+    Optionally exclude a specific page (the one being saved).
+    """
+    stmt = (
+        update(InfoPage)
+        .where(
+            InfoPage.replaces_tab == tab,
+        )
+        .values(replaces_tab=None, updated_at=datetime.now(UTC))
+    )
+    if exclude_page_id is not None:
+        stmt = stmt.where(InfoPage.id != exclude_page_id)
+
+    await db.execute(stmt)
+
+
 async def reorder_info_pages(db: AsyncSession, items: list[dict]) -> None:
     """Bulk update sort_order for info pages.
 

app/database/models.py

@@ -3713,5 +3713,6 @@ class InfoPage(Base):
     is_active = Column(Boolean, nullable=False, default=True, server_default='true')
     sort_order = Column(Integer, nullable=False, default=0, server_default='0')
     icon = Column(String(50), nullable=True)
+    replaces_tab = Column(String(20), nullable=True)  # 'faq', 'rules', 'privacy', 'offer', or null
     created_at = Column(AwareDateTime(), server_default=func.now())
     updated_at = Column(AwareDateTime(), server_default=func.now(), onupdate=func.now())

migrations/alembic/versions/0067_add_replaces_tab_to_info_pages.py

@@ -0,0 +1,28 @@
+"""add replaces_tab to info_pages
+
+Revision ID: 0067
+Revises: 0066
+Create Date: 2026-04-21
+
+"""
+
+from typing import Sequence, Union
+
+import sqlalchemy as sa
+from alembic import op
+
+revision: str = '0067'
+down_revision: Union[str, None] = '0066'
+branch_labels: Union[str, Sequence[str], None] = None
+depends_on: Union[str, Sequence[str], None] = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        'info_pages',
+        sa.Column('replaces_tab', sa.String(20), nullable=True),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column('info_pages', 'replaces_tab')