# Architectural Decision Log (ADL)

## [2026-08-09] - ADL-001: Distributed Local-First System Baseline

- **Status**: Accepted
- **Context**: Design a multi-platform (Windows, Linux, Android, Headless) productivity engine for time, project, and note management without centralized servers.
- **Decision**: Adopted Rust core with SQLCipher local storage, Automerge CRDT delta sync over libp2p, and Flutter presentation layer bound via C-FFI.

## [2026-08-19] - ADL-003: chronogrid_core Crate – SQLCipher 4.x Database Initializer

- **Status**: Accepted
- **Context**: Task 1.3 required implementing the `chronogrid_core` crate with SQLCipher 4.x encrypted database initialization matching `docs/API_CONTRACTS/schema.sql`.
- **Decision**:
  - `rusqlite` v0.31 with `bundled-sqlcipher-vendored-openssl` feature bundles both SQLCipher and OpenSSL, ensuring a hermetic build with no external C library dependencies.
  - The 32-byte Argon2id-derived master key is passed as a **raw hex key** via `PRAGMA key = "x'…'"`, bypassing SQLCipher's internal PBKDF2 derivation since Argon2id already provides equivalent or stronger protection.
  - `PRAGMA cipher_compatibility = 4` enforces SQLCipher 4.x defaults (AES-256-CBC, HMAC-SHA512 page auth, 64 KiB page size).
  - `PRAGMA foreign_keys = ON` is set on every connection per the schema specification.
  - The canonical schema SQL from `docs/API_CONTRACTS/schema.sql` is embedded via `include_str!` at compile time, ensuring single-source-of-truth alignment without runtime file I/O.
  - Post-initialization validation confirms all 6 expected tables exist (`namespaces`, `projects`, `tasks`, `notes`, `task_note_links`, `ingestion_logs`) plus 4 indexes.
  - `Database` struct provides `open(path, key)` for file-backed and `open_in_memory(key)` for test databases; key length is validated at 32 bytes.
  - 11 unit tests cover: table/index creation, FK enforcement, cascade deletes, wrong-key rejection, key length validation, schema idempotency, and CRUD round-trips across all tables.

## [2026-08-20] - ADL-004: chronogrid_core – Automerge CRDT Integration for Task & Note Registers

- **Status**: Accepted
- **Context**: Task 1.4 required integrating the Automerge CRDT engine into `chronogrid_core` so task and note entities support offline-first LWW register mutations with HLC-based causal ordering.
- **Decision**:
  - Added `automerge = "0.5"` (resolved to v0.5.12) and `uuid = "1"` with `v4` feature to `chronogrid_core/Cargo.toml`.
  - Extended `schema.sql` with `crdt_docs` table (`entity_id TEXT PK`, `entity_type TEXT`, `doc_bytes BLOB`, `updated_at INTEGER`) and `idx_crdt_docs_type` index.
  - Implemented `crdt/` sub-module: `Hlc` (Hybrid Logical Clock with `tick()`/`update()`/`Display`/`FromStr`), `CrdtDoc` (generic Automerge wrapper with typed scalar accessors), `TaskCrdt` (11 mutable fields), `NoteCrdt` (4 mutable fields).
  - Each entity mutation stamps the document with an advancing HLC timestamp. Fork/merge delegates to Automerge's deterministic conflict resolution.
  - `Database` gained `save_crdt_doc()`, `load_crdt_doc()`, `delete_crdt_doc()` for serialized Automerge blob persistence.
  - Added `CoreError::Crdt` and `CoreError::HlcParse` error variants.
  - 45 unit tests (all passing): HLC ordering/parse, all scalar types, save/load/fork/merge round-trips, CRDT doc DB persistence, schema validation with `crdt_docs` table.
  - Full ADR at `docs/ARCHITECTURE/ADR/0004-core-automerge-crdt-integration.md`.

## [2026-08-20] - ADL-005: chronogrid_ffi Crate – Flutter Rust Bridge v2 FFI Layer

- **Status**: Accepted
- **Context**: Task 1.5 required generating `flutter_rust_bridge` FFI bindings to bridge all Rust storage, CRDT, and cryptographic methods to the Flutter/Dart presentation layer.
- **Decision**:
  - Created `crates/chronogrid_ffi/` crate with `cdylib` + `staticlib` + `lib` targets, depending on `chronogrid_core`, `chronogrid_crypto`, `flutter_rust_bridge = "=2.7.0"`, and `anyhow = "1"`.
  - API uses a **serialized-bytes pattern**: CRDT documents cross FFI as `Vec<u8>` (Automerge binary); read functions return DTO structs (`FfiTaskData`, `FfiNoteData`, `FfiDerivedKey`).
  - Global `Engine` singleton (`Mutex<Option<Engine>>`) holds the `Database` connection + `Hlc` clock. Thread-safe `with_engine()` / `with_engine_mut()` helpers provide access from FRB's isolate thread pool.
  - 38 public FFI functions across 5 API modules: `engine` (init/close/status), `database` (CRDT doc persistence), `crypto` (key derivation + platform-gated keychain), `task_crdt` (18 create/read/set/clear/merge ops), `note_crdt` (8 create/read/set/clear/merge ops).
  - All fallible functions return `anyhow::Result<T>`, which FRB v2 maps to Dart exceptions.
  - Keychain functions compile on all platforms but return an error on Android (delegated to Flutter KeyStore bridge).
  - `flutter_rust_bridge.yaml` configures codegen: Rust input from `api/`, Dart output to `apps/chronogrid_flutter/lib/src/rust/`.
  - Flutter `pubspec.yaml` updated with `flutter_rust_bridge: ^2.7.0`, `ffi: ^2.1.0`, `meta: ^1.11.0`.
  - 25 unit tests (all passing): engine lifecycle, DB CRDT doc persistence, task/note CRDT create/read/mutate/merge round-trips, crypto derivation, stateless read validation, no-engine error paths.
  - Full ADR at `docs/ARCHITECTURE/ADR/0005-ffi-bridge-flutter-rust-bridge.md`.

## [2026-08-09] - ADL-002: chronogrid_crypto Crate – Argon2id KDF & OS Keychain

- **Status**: Accepted
- **Context**: Task 1.2 required implementing the `chronogrid_crypto` crate with Argon2id master-key derivation and OS-native keychain bindings per `docs/ARCHITECTURE/02-security-and-crypto.md`.
- **Decision**:
  - Argon2id parameters pinned: 64 MiB memory, 3 iterations, 4 threads, 16-byte random salt, 32-byte output.
  - `DerivedKey` struct implements `Zeroize + Drop` to scrub sensitive memory on scope exit.
  - OS keychain abstracted via `keyring` crate v3 (Windows Credential Manager / DPAPI, Linux SecretService / libsecret). Android keychain is excluded (`cfg(not(target_os = "android"))`) and will be handled by Flutter KeyStore bridge in Task 1.5.
  - Raw key material is Base64-encoded before credential-store insertion for UTF-8 backend compatibility.
  - Inline Base64 encode/decode helpers avoid adding an external Base64 dependency.