diff --git a/Cargo.lock b/Cargo.lock
index 6cc1bf2..ae216f5 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -102,12 +102,37 @@ version = "1.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1505bd5d3d116872e7271a6d4e16d81d0c8570876c8de68093a09ac269d8aac0"
 
+[[package]]
+name = "autocfg"
+version = "1.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f2032f911046de80f0a198e0901378627c33f59ea0ac00e363d481118bd70a53"
+
 [[package]]
 name = "base64"
 version = "0.22.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "72b3254f16251a8381aa12e40e3c4d2f0199f8c6508fbecb9d91f575e0fbb8c6"
 
+[[package]]
+name = "bit-set"
+version = "0.11.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "56d87354e4229f54a44f7bf2435906a4656dba36026ab6eaca629a2c436a691c"
+dependencies = [
+ "bit-vec",
+]
+
+[[package]]
+name = "bit-vec"
+version = "0.10.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5727b15fa97d4f4fee0a3b7c3d550ed0269f54329207b86388de918604e31269"
+dependencies = [
+ "borsh",
+ "serde",
+]
+
 [[package]]
 name = "bitflags"
 version = "2.13.2"
@@ -123,6 +148,30 @@ dependencies = [
  "generic-array",
 ]
 
+[[package]]
+name = "borsh"
+version = "1.8.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "553c5d846a6ba5150c65e3b1b8ec073bcf1abc20f9b7220de384a4443ea4e20a"
+dependencies = [
+ "borsh-derive",
+ "bytes",
+ "cfg_aliases",
+]
+
+[[package]]
+name = "borsh-derive"
+version = "1.8.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "12cdfe656708a01f89b451a7d36466e6fe6c414de0aa18fc54f864f6f9ca9f56"
+dependencies = [
+ "once_cell",
+ "proc-macro-crate",
+ "proc-macro2",
+ "quote",
+ "syn 3.0.9",
+]
+
 [[package]]
 name = "bumpalo"
 version = "3.20.3"
@@ -174,6 +223,12 @@ version = "1.0.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "4e7648175b45a9a48536d676f68d918270699102aa8dab5496df06904c914600"
 
+[[package]]
+name = "cfg_aliases"
+version = "0.2.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f079e83a288787bcd14a6aea84cee5c87a67c5a3e660c30f557a3d24761b3527"
+
 [[package]]
 name = "chacha20"
 version = "0.10.2"
@@ -514,6 +569,12 @@ dependencies = [
  "syn 3.0.9",
 ]
 
+[[package]]
+name = "dyn-clone"
+version = "1.0.20"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d0881ea181b1df73ff77ffaaf9c7544ecc11e82fba9b5f27b262a3c73a332555"
+
 [[package]]
 name = "either"
 version = "1.19.0"
@@ -1256,6 +1317,15 @@ dependencies = [
  "bitflags",
 ]
 
+[[package]]
+name = "num-traits"
+version = "0.2.19"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "071dfc062690e90b734c0b2273ce72ad0ffa95f0c74596bc250dcfd960262841"
+dependencies = [
+ "autocfg",
+]
+
 [[package]]
 name = "object"
 version = "0.40.0"
@@ -1352,6 +1422,15 @@ dependencies = [
  "zerovec",
 ]
 
+[[package]]
+name = "proc-macro-crate"
+version = "3.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e67ba7e9b2b56446f1d419b1d807906278ffa1a658a8a5d8a39dcb1f5a78614f"
+dependencies = [
+ "toml_edit",
+]
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.107"
@@ -1361,6 +1440,26 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "proptest"
+version = "1.12.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b8530004ccb15eae51c7e40009fbe317f341f804db54dc033eec1c50be28cfa0"
+dependencies = [
+ "bit-set",
+ "bit-vec",
+ "bitflags",
+ "chacha20",
+ "core_detect",
+ "num-traits",
+ "rand",
+ "rand_xorshift",
+ "regex-syntax",
+ "rusty-fork",
+ "tempfile",
+ "unarray",
+]
+
 [[package]]
 name = "pulley-interpreter"
 version = "49.0.3"
@@ -1384,6 +1483,12 @@ dependencies = [
  "syn 2.0.119",
 ]
 
+[[package]]
+name = "quick-error"
+version = "1.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a1d01941d82fa2ab50be1e79e6714289dd7cde78eba4c074bc5a4374f650dfe0"
+
 [[package]]
 name = "quote"
 version = "1.0.47"
@@ -1416,6 +1521,15 @@ version = "0.10.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "63b8176103e19a2643978565ca18b50549f6101881c443590420e4dc998a3c69"
 
+[[package]]
+name = "rand_xorshift"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "60aa6af80be32871323012e02e6e65f8a7cc7890931ae421d217ad8fe0df2ccf"
+dependencies = [
+ "rand_core",
+]
+
 [[package]]
 name = "rayon"
 version = "1.12.0"
@@ -1456,6 +1570,26 @@ dependencies = [
  "thiserror 1.0.69",
 ]
 
+[[package]]
+name = "ref-cast"
+version = "1.0.27"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7e440fb4e4b4147295338efb76001ab9e4efc0e5839df2c47fc5ac2381d365c3"
+dependencies = [
+ "ref-cast-impl",
+]
+
+[[package]]
+name = "ref-cast-impl"
+version = "1.0.27"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "92ecd8964f8453721699a1ed72037b0db49ce2f5a5138486ee89bed6f67cdf3a"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 3.0.9",
+]
+
 [[package]]
 name = "regalloc2"
 version = "0.15.2"
@@ -1471,6 +1605,12 @@ dependencies = [
  "smallvec",
 ]
 
+[[package]]
+name = "regex-syntax"
+version = "0.8.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d6f6ff9a378485b298a5286656da665ba74413d36db0979633275d2e708145d4"
+
 [[package]]
 name = "ring"
 version = "0.17.14"
@@ -1561,6 +1701,18 @@ version = "1.0.23"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cf54715a573b99ac80df0bc206da022bcd442c974952c7b9720069370852e21f"
 
+[[package]]
+name = "rusty-fork"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cc6bf79ff24e648f6da1f8d1f011e9cac26491b619e6b9280f2b47f1774e6ee2"
+dependencies = [
+ "fnv",
+ "quick-error",
+ "tempfile",
+ "wait-timeout",
+]
+
 [[package]]
 name = "same-file"
 version = "1.0.6"
@@ -1594,6 +1746,9 @@ dependencies = [
 name = "sausage-interface"
 version = "0.1.0"
 dependencies = [
+ "proptest",
+ "schemars",
+ "serde",
  "serde_json",
 ]
 
@@ -1612,6 +1767,31 @@ version = "0.1.0"
 name = "sausage-vfs"
 version = "0.1.0"
 
+[[package]]
+name = "schemars"
+version = "1.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ab508826f74a77ca9d5aba6ff19b522583ee3eaf28a19384ff3d0e5835fadf6e"
+dependencies = [
+ "dyn-clone",
+ "ref-cast",
+ "schemars_derive",
+ "serde",
+ "serde_json",
+]
+
+[[package]]
+name = "schemars_derive"
+version = "1.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e1c3a92094fa7d61aa124645844facb6b554dfc797136d0f5fd1f890e2bffc69"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "serde_derive_internals",
+ "syn 3.0.9",
+]
+
 [[package]]
 name = "scopeguard"
 version = "1.2.0"
@@ -1658,6 +1838,17 @@ dependencies = [
  "syn 3.0.9",
 ]
 
+[[package]]
+name = "serde_derive_internals"
+version = "0.30.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f852137cce035d6a4df67ccce505ff6b3e9fd3a10e3e52b24dc71e650bb1a9bd"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 3.0.9",
+]
+
 [[package]]
 name = "serde_json"
 version = "1.0.154"
@@ -2014,6 +2205,12 @@ version = "1.20.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b6f5e870be6c3b371b77fe0ee0bafb859fa4964b4404c27de1d380043c4dda20"
 
+[[package]]
+name = "unarray"
+version = "0.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "eaea85b334db583fe3274d12b4cd1880032beab409c0d774be044d4480ab9a94"
+
 [[package]]
 name = "unicode-ident"
 version = "1.0.27"
@@ -2072,6 +2269,15 @@ version = "0.9.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0b928f33d975fc6ad9f86c8f283853ad26bdd5b10b7f1542aa2fa15e2289105a"
 
+[[package]]
+name = "wait-timeout"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09ac3b126d3914f9849036f826e054cbabdc8519970b8998ddaf3b5bd3c65f11"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "walkdir"
 version = "2.5.0"
diff --git a/PROPOSAL.md b/PROPOSAL.md
index f314408..4844762 100644
--- a/PROPOSAL.md
+++ b/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. |
diff --git a/interface/Cargo.toml b/interface/Cargo.toml
index 4ce14ef..56b93af 100644
--- a/interface/Cargo.toml
+++ b/interface/Cargo.toml
@@ -6,3 +6,8 @@ description = "Sausage plugin interfaces: OpenRPC documents, the compatibility c
 
 [dependencies]
 serde_json = "1"
+
+[dev-dependencies]
+proptest = "1"
+schemars = "1"
+serde = { version = "1", features = ["derive"] }