# 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.

## [2026-08-09] - 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.