# fai-module-sdk

Stable, ergonomic Rust surface for writing F∆I Platform modules.

A module written against this crate looks like:

```rust
use fai_module_sdk::prelude::*;

#[fai_module]
fn invoke(_ctx: Context, inputs: Inputs) -> Result<Outputs, ModuleError> {
    let text = inputs.require_text("input")?;
    Ok(Outputs::new().with_text("output", format!("echo: {text}")))
}
```

That single function — plus a `Cargo.toml` listing
`fai-module-sdk` as a dependency — is the entire module. The
`#[fai_module]` macro generates the `wit_bindgen` invocation, the
`Guest` implementation, the type conversions, and the
`wit_bindgen::export!` glue behind the scenes.

## What the SDK gives you

| You get | Instead of |
|---------|-----------|
| `Inputs::require_text("name")` | manual `match payload { Payload::Text(s) => ..., _ => ... }` |
| `Outputs::new().with_json(...)?` | building `Vec<(String, Payload)>` by hand |
| `ModuleError::invalid_input("...")` | constructing WIT `invocation-error` variants |
| `#[fai_module]` | `wit_bindgen::generate!` + `Guest` impl + `export!` + `#![allow(unsafe_op_in_unsafe_fn)]` |

## Stability

The SDK insulates module code from the underlying WIT contract
(`chain:platform`, frozen at v1.0 in the platform repo). The
WIT may evolve in additive minor versions or, eventually, a
coordinated v2.0; the SDK absorbs that change so existing
module code keeps compiling.

The SDK ships its own copy of `wit/world.wit` so that the
proc-macro can embed the contract via `include_str!` at compile
time. A snapshot test (`crates/fai-module-sdk/tests/wit_freeze.rs`)
asserts the SHA-256 matches the platform's frozen hash — if the
two ever drift, CI fails.

## Versioning

| Track | Stability |
|-------|-----------|
| WIT contract (`chain:platform`) | Frozen at v1.0 in the platform repo |
| `fai-module-sdk` Rust API | Semver; v0.x while ergonomics evolve |
| Per-module versions | Each module repo's own concern |

## License

Apache-2.0. See `LICENSE`.

Author: Dr. Stefan Flemming, Flemming.AI <platform@flemming.ai>
Repository: https://git.flemming.ai/fai/module-sdk-rust