PROPOSAL.md: sausage-interface crate and #[on_stop]

PROPOSAL.md

@@ -516,14 +516,21 @@ Tests:
 
 ## 13. The SDK
 
-Two crates: `sausage-plugin`, and `sausage-plugin-macros`, which
-`sausage-plugin` re-exports. A plugin depends only on `sausage-plugin`. The
-SDK also re-exports `serde` and `schemars` for the macros.
+Three crates:
+
+- `sausage-plugin`: the SDK. A plugin depends only on this crate. It
+  re-exports the macros, `serde`, and `schemars`.
+- `sausage-plugin-macros`: the macros.
+- `sausage-interface`: the OpenRPC documents, the compatibility check
+  (section 11.2), and the generator of client code. The macros and the host
+  both use it, so `import!` and `/proc/core/plugins/<name>/client.rs` give
+  the same code.
 
 | Item | Purpose |
 | --- | --- |
 | `#[rpc]` | Makes an `impl` an interface. On the main interface: `#[rpc(endpoints(name = Type), grace_seconds = N)]`. |
 | `#[on_retired]` | Marks the method that answers `rpc.retired`. |
+| `#[on_stop]` | Marks the stop hook: an optional method that runs at EOF on stdin (section 4.6). |
 | `#[schema]` | For each type that a method takes or returns: adds the serde and schemars derives, and checks the subset of section 11.2. |
 | `run(T)` | In `main`: serves the main interface on stdin and stdout. |
 | `call(method, params)` | An untyped call. Returns a JSON value. |