feat(derive): expose checked form resource constants

Have #[slhx::form] emit an associated FORM resource so checked form handlers can be called with TodoInput::FORM-style values instead of generated_resource.typed::<T>() noise.

req: form/001

req: form/004

req: form/006

req: codegen/004

examples/kanban/src/lib.rs

@@ -64,7 +64,7 @@ mod tests {
             ui::board::slots::notice.text("queued")
         }
 
-        let effect = inspect(create_card(ui::board::forms::create_card.typed::<CreateCard>()));
+        let effect = inspect(create_card(CreateCard::FORM));
 
         assert!(effect.has_slot(ui::board::slots::notice));
         assert!(matches!(effect.ops(), [Effect::Put { payload: Payload::Text(_), .. }]));

examples/techdemo/src/lib.rs

@@ -55,9 +55,7 @@ mod tests {
             ui::control_center::slots::notice.text("queued")
         }
 
-        let batch = inspect(launch_work(
-            ui::control_center::forms::launch_work.typed::<LaunchWork>(),
-        ));
+        let batch = inspect(launch_work(LaunchWork::FORM));
 
         assert!(batch.has_slot(ui::control_center::slots::notice));
         assert!(matches!(batch.ops(), [Effect::Put { payload: Payload::Text(_), .. }]));

examples/v0/src/lib.rs

@@ -66,7 +66,7 @@ mod tests {
             ui::slots::todo_list.text("queued")
         }
 
-        let effect = inspect(add_todo(ui::forms::new_todo.typed::<TodoInput>()));
+        let effect = inspect(add_todo(TodoInput::FORM));
 
         assert!(effect.has_slot(ui::slots::todo_list));
         assert!(matches!(effect.ops(), [Effect::Put { payload: Payload::Text(_), .. }]));
@@ -103,7 +103,7 @@ mod tests {
             ui::slots::wizard_step.text("queued")
         }
 
-        let effect = inspect(next_step(ui::forms::wizard_input.typed::<WizardInput>()));
+        let effect = inspect(next_step(WizardInput::FORM));
 
         assert!(effect.has_slot(ui::slots::wizard_step));
         assert!(matches!(effect.ops(), [Effect::Put { payload: Payload::Text(_), .. }]));
@@ -158,7 +158,7 @@ mod tests {
             ui::slots::login_status.text("queued")
         }
 
-        let effect = inspect(login(ui::forms::credentials.typed::<Credentials>()));
+        let effect = inspect(login(Credentials::FORM));
 
         assert!(effect.has_slot(ui::slots::login_status));
         assert!(matches!(effect.ops(), [Effect::Put { payload: Payload::Text(_), .. }]));

slhx-derive/src/lib.rs

@@ -88,9 +88,18 @@ pub fn surface(_attr: TokenStream, item: TokenStream) -> TokenStream {
 pub fn form(attr: TokenStream, item: TokenStream) -> TokenStream {
     let form_name = parse_macro_input!(attr as LitStr).value();
     let form_struct = parse_macro_input!(item as ItemStruct);
-    let errors = form_contract_errors(&form_name, &form_struct);
+    let Some(syms_path) = syms_path() else {
+        let message = "#[slhx::form] requires OUT_DIR; run inside a Cargo crate with slhx_build::app() in build.rs";
+        return quote!(
+            #form_struct
+            compile_error!(#message);
+        )
+        .into();
+    };
+    let errors = form_contract_errors(&syms_path, &form_name, &form_struct);
     if errors.is_empty() {
         let ident = &form_struct.ident;
+        let resource_id = form_resource_id(&syms_path, &form_name).expect("checked form exists in slhx.syms");
         let mut generics = form_struct.generics.clone();
         for ty in form_parser_types(&form_struct) {
             generics.make_where_clause().predicates.push(parse_quote!(#ty: ::slhx::FormValue));
@@ -99,6 +108,9 @@ pub fn form(attr: TokenStream, item: TokenStream) -> TokenStream {
         quote!(
             #form_struct
             impl #impl_generics ::slhx::FormModel for #ident #ty_generics #where_clause {}
+            impl #impl_generics #ident #ty_generics #where_clause {
+                pub const FORM: ::slhx::Form<Self> = ::slhx::Form::new(#resource_id);
+            }
         )
         .into()
     } else {
@@ -281,17 +293,14 @@ struct GeneratedFormField {
     multiple: bool,
 }
 
-fn form_contract_errors(form_name: &str, form_struct: &ItemStruct) -> Vec<String> {
-    let Some(syms_path) = syms_path() else {
-        return vec!["#[slhx::form] requires OUT_DIR; run inside a Cargo crate with slhx_build::app() in build.rs".to_string()];
-    };
+fn form_contract_errors(syms_path: &PathBuf, form_name: &str, form_struct: &ItemStruct) -> Vec<String> {
     if !syms_path.exists() {
         return vec![format!(
             "#[slhx::form] could not find {}; add slhx_build::app().run()? to build.rs or check template generation",
             syms_path.display()
         )];
     }
-    let expected = form_fields(&syms_path, form_name);
+    let expected = form_fields(syms_path, form_name);
     if expected.is_empty() {
         return vec![format!(
             "unknown slhx form `{form_name}`; add data-slhx-form=\"{form_name}\" to a template or rename this form binding"
@@ -380,6 +389,20 @@ fn generic_inner_type<'a>(ty: &'a Type, name: &str) -> Option<&'a Type> {
     })
 }
 
+fn form_resource_id(path: &PathBuf, form_name: &str) -> Option<u32> {
+    let syms = std::fs::read_to_string(path).ok()?;
+    syms.lines().find_map(|line| {
+        let mut fields = line.split('\t');
+        if !matches!(fields.next(), Some("form")) {
+            return None;
+        }
+        if fields.nth(1)? != form_name {
+            return None;
+        }
+        fields.next()?.parse().ok()
+    })
+}
+
 fn form_fields(path: &PathBuf, form_name: &str) -> Vec<GeneratedFormField> {
     let Ok(syms) = std::fs::read_to_string(path) else {
         return Vec::new();

slhx-derive/tests/compile_fail.rs

@@ -423,6 +423,10 @@ struct CreateTodo {
 fn create(_form: slhx::Form<CreateTodo>) -> impl slhx::IntoEffect {
     slhx::event("created", "")
 }
+
+fn smoke() {
+    let _ = create(CreateTodo::FORM);
+}
 "#,
     );