# 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.

## [2026-08-09] - 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.