# 02 - Architecture

## Local-first rule

SQLite is the runtime source of truth.
MariaDB is sync transport plus setup and migration tooling.

```text
browser -> Gin handlers -> SQLite
                        -> pending_changes
background sync <------> MariaDB
```

Rules:
- user CRUD must continue when MariaDB is offline;
- runtime handlers and pages must read and write SQLite only;
- MariaDB access in runtime code is allowed only inside sync and setup flows;
- no live MariaDB fallback for reads that already exist in local cache.

## Sync contract

Bidirectional:
- projects;
- configurations;
- `vendor_spec`;
- pending change metadata.

Pull-only:
- components;
- pricelists and pricelist items;
- partnumber books and partnumber book items.

Readiness guard:
- every sync push/pull runs a preflight check;
- blocked sync returns `423 Locked` with a machine-readable reason;
- local work continues even when sync is blocked.
- sync metadata updates must preserve project `updated_at`; sync time belongs in `synced_at`, not in the user-facing last-modified timestamp.

## Pricing contract

Prices come only from `local_pricelist_items`.

Rules:
- `local_components` is metadata-only;
- quote calculation must not read prices from components;
- latest pricelist selection ignores snapshots without items;
- auto pricelist mode stays auto and must not be persisted as an explicit resolved ID.

## Configuration versioning

Configuration revisions are append-only snapshots stored in `local_configuration_versions`.

Rules:
- create a new revision only when spec or price content changes;
- rollback creates a new head revision from an old snapshot;
- rename, reorder, project move, and similar operational edits do not create a new revision snapshot;
- current revision pointer must be recoverable if legacy or damaged rows are found locally.

## Naming collisions

UI-driven rename and copy flows use one suffix convention for conflicts.

Rules:
- configuration and variant names must auto-resolve collisions with `_копия`, then `_копия2`, `_копия3`, and so on;
- copy checkboxes and copy modals must prefill `_копия`, not ` (копия)`;
- the literal variant name `main` is reserved and must not be allowed for non-main variants.

## Vendor BOM contract

Vendor BOM is stored in `vendor_spec` on the configuration row.

Rules:
- PN to LOT resolution uses the active local partnumber book;
- canonical persisted mapping is `lot_mappings[]`;
- QuoteForge does not use legacy BOM tables such as `qt_bom`, `qt_lot_bundles`, or `qt_lot_bundle_items`.