plugin: implement component model runtime

resources/plugin/wit/yoi-host-v1.wit

@@ -0,0 +1,15 @@
+package yoi:host@1.0.0;
+
+/// Grant-bound HTTPS host API. Importing this interface does not grant
+/// authority; package grants are checked before registration/execution and on
+/// every host call.
+interface https {
+  request: func(request-json: string) -> string;
+}
+
+/// Grant-bound filesystem host API. No ambient WASI filesystem is exposed.
+interface fs {
+  read: func(request-json: string) -> string;
+  list: func(request-json: string) -> string;
+  write: func(request-json: string) -> string;
+}

resources/plugin/wit/yoi-plugin-tool-v1.wit

@@ -0,0 +1,11 @@
+package yoi:plugin@1.0.0;
+
+world tool {
+  import yoi:host/https@1.0.0;
+  import yoi:host/fs@1.0.0;
+
+  /// Execute a manifest-declared Tool. `input-json` is the normal Tool input
+  /// JSON and the returned string is the same ToolOutput JSON accepted by the
+  /// legacy raw-Wasm ABI.
+  export call: func(tool-name: string, input-json: string) -> string;
+}