chore: update agents.md (#3126)

<!-- Thank you for making a PR! Bug fixes are always welcome, but if
you're adding a new feature or changing an existing one, we'd really
appreciate if you open an issue, post on the forum, or drop in on
Discord -->

## Checks
- [ ] I am happy for maintainers to push small adjustments to this PR,
to speed up the review cycle
- [ ] I have checked that there are no existing pull requests for the
same thing

AGENTS.md

@@ -0,0 +1,71 @@
+# Atuin
+
+Shell history tool. Replaces your shell's built-in history with a SQLite database, adds context (cwd, exit code, duration, hostname), and optionally syncs across machines with end-to-end encryption.
+
+## Workspace crates
+
+```
+atuin                  CLI binary + TUI (clap, ratatui, crossterm)
+atuin-client           Client library: local DB, encryption, sync, settings
+atuin-common           Shared types, API models, utils
+atuin-daemon           Background gRPC daemon (tonic) for shell hooks
+atuin-dotfiles         Alias/var sync via record store
+atuin-history          Sorting algorithms, stats
+atuin-kv               Key-value store (synced)
+atuin-scripts          Script management (minijinja)
+atuin-server           HTTP sync server (axum) - lib + standalone binary
+atuin-server-database  Database trait for server
+atuin-server-postgres  Postgres implementation (sqlx)
+atuin-server-sqlite    SQLite implementation (sqlx)
+```
+
+## Two sync protocols
+
+- **V1 (legacy)**: Syncs history entries directly. Being phased out. Toggleable via `sync_v1_enabled`.
+- **V2 (current)**: Record store abstraction. All data types (history, KV, aliases, vars, scripts) share the same sync infrastructure using tagged records. Envelope-encrypted with PASETO V4 and per-record CEKs.
+
+## Encryption
+
+- **V1**: XSalsa20Poly1305 (secretbox). Key at `~/.local/share/atuin/key`.
+- **V2**: PASETO V4 Local (XChaCha20-Poly1305 + Blake2b). Envelope encryption: each record gets a random CEK wrapped with the master key. Record metadata (id, idx, version, tag, host) is authenticated as implicit assertions.
+
+## Databases
+
+- **Client**: SQLite everywhere. Separate DBs for history, record store, KV, scripts. All use sqlx + WAL mode.
+- **Server**: Postgres (primary) or SQLite. Auto-detected from URI prefix.
+- Migrations live alongside each crate. Never modify existing migrations, only add new ones.
+
+## Hot paths
+
+`history start`, `history end`, and `init` skip database initialization for latency. Don't add DB calls to these without good reason.
+
+## Conventions
+
+- Rust 2024 edition, toolchain 1.93.
+- Errors: `eyre::Result` in binaries, `thiserror` for typed errors in libraries.
+- Async: tokio. Client uses `current_thread`; server uses `multi_thread`.
+- `#![deny(unsafe_code)]` on client/common, `#![forbid(unsafe_code)]` on server.
+- Clippy: `pedantic` + `nursery` on main crate. CI enforces `-D warnings -D clippy::redundant_clone`.
+- Format: `cargo fmt`. Only non-default: `reorder_imports = true`.
+- IDs: UUIDv7 (time-ordered), newtype wrappers (`HistoryId`, `RecordId`, `HostId`).
+- Serialization: MessagePack for encrypted payloads, JSON for API, TOML for config.
+- Storage traits: `Database` (client), `Store` (record store), `Database` (server) -- all `async_trait`.
+- History builders: `HistoryImported`, `HistoryCaptured`, `HistoryFromDb` with compile-time field validation.
+- Feature flags: `client`, `sync`, `daemon`, `clipboard`, `check-update`.
+
+## Testing
+
+- Unit tests inline with `#[cfg(test)]`, async via `#[tokio::test]`.
+- Integration tests in `crates/atuin/tests/` need Postgres (`ATUIN_DB_URI` env var).
+- Use `":memory:"` SQLite for unit tests needing a database.
+- Runner: `cargo nextest`.
+- Benchmarks: `divan` in `atuin-history`.
+
+## Build and check
+
+```sh
+cargo build
+cargo test
+cargo clippy -- -D warnings
+cargo fmt --check
+```