test(derive): close sixth mutation shard

Exercise malformed parameter manifests, handler patterns, app diagnostics, and registration guards; delete an unreachable empty-handler branch and narrowly classify quote-owned parse invariants.

req: derive_app/001

req: component/003

req: derive_handler/003

req: test/020

req: test/021

req: test/022

req: test/023

.cargo/mutants.toml

@@ -24,6 +24,9 @@
 # - Rust-fact named fields always carry identifiers by syn's type contract. Per-entry
 #   and recursive read_dir errors cannot be injected portably after the parent opens;
 #   parent-open, source-read, and parse failures remain explicitly proven.
+# - Registry-helper syntax is emitted entirely from quote-owned static tokens. Its
+#   parse succeeds by construction; expect/unwrap and expect-message mutations are
+#   equivalent, while exact generated registration and public diagnostics are proven.
 exclude_re = [
   "test_process_try_wait",
   "test_process_poll_delay",
@@ -48,4 +51,8 @@ exclude_re = [
   "replace chars.next\\(\\)\\? with chars.next\\(\\).unwrap\\(\\) in context_type_for_heml_path",
   "replace entry\\? with entry.unwrap\\(\\) in collect_rust_struct_facts",
   "replace collect_rust_struct_facts.*\\? with collect_rust_struct_facts.*unwrap\\(\\) in collect_rust_struct_facts",
+  'replace syn::parse2.* with syn::parse2.*unwrap\(\) in add_app_registry_helper',
+  'replace "generated app registry helper parses" with "" in add_app_registry_helper',
+  'replace "generated component register helper parses" with "" in add_component_register_helper',
+  'replace "generated component state register helper parses" with "" in add_component_register_helper',
 ]

PLAN.md

@@ -21,7 +21,7 @@
 - [ ] **State:** In progress — the package-native capped xtask entry point is reachable, rejects unknown packages and invalid shards, propagates mutest failure, and mutation-tests `hemx-axum`, `hemx-build`, `hemx-core`, `hemx-js`, and the full `hemx-test` package cleanly; full package closure remains.
 - **User value:** maintainers can run one bounded repository command and trust that meaningful Rust logic across every mutation-applicable library is either killed or explicitly justified.
 - **Build:** add a capped `hemx-xtask` mutation command that invokes `/opt/repositories/mutest`/`mutest` through package-native test targets rather than the broken workspace-wide example path; enumerate only current mutation-applicable library/proc-macro packages; finish adversarial tests or simplify code until every survivor is classified; keep equivalent, invariant-only, and infrastructure-inapplicable classifications inspectable and minimal; document the exact local release command in the existing readiness surface.
-- **Blocked by:** none; broad survivors currently remain in `hemx-derive` and `hemx-lsp` outside already-clean focused contracts. The xtask mutation runner now creates shard output parents before invoking mutest, fixing first-use failure for newly sharded packages. `hemx-derive` public shards `1/8` through `5/8` are clean. Shard `5/8` passed with 61 mutants (57 caught, 4 unviable) after fail-closed generated field-name validation and deletion of a redundant empty-parameter branch. Shards `6/8` through `8/8` remain. The mutation entry point accepts validated one-based `SHARD/TOTAL` operands, maps them to native zero-based shards, uses shard-specific output directories, grants repo-owned compiler probes a 120-second floor, and preserves the unsharded gate. All eight deterministic `hemx-build` shards now pass: 1,304 mutants total, 1,070 caught and 234 unviable, including final shard `8/8` with 159 mutants (139 caught, 20 unviable). The complete 470-mutant `hemx-axum` package gate passes with 262 caught and 208 unviable after public page/form/multipart/registry/response/runtime proofs and narrow classification of infallible header parsing and streamed multipart unwrap-equivalent mutants.
+- **Blocked by:** none; broad survivors currently remain in `hemx-derive` and `hemx-lsp` outside already-clean focused contracts. The xtask mutation runner now creates shard output parents before invoking mutest, fixing first-use failure for newly sharded packages. `hemx-derive` public shards `1/8` through `6/8` are clean. Shard `6/8` passed with 60 mutants (50 caught, 10 unviable) after malformed parameter-manifest, handler-pattern, app diagnostic, and component registration guard coverage; an unreachable empty-handler branch was deleted, and static quote-owned syntax parsing is narrowly classified as invariant-equivalent. Shards `7/8` and `8/8` remain. The mutation entry point accepts validated one-based `SHARD/TOTAL` operands, maps them to native zero-based shards, uses shard-specific output directories, grants repo-owned compiler probes a 120-second floor, and preserves the unsharded gate. All eight deterministic `hemx-build` shards now pass: 1,304 mutants total, 1,070 caught and 234 unviable, including final shard `8/8` with 159 mutants (139 caught, 20 unviable). The complete 470-mutant `hemx-axum` package gate passes with 262 caught and 208 unviable after public page/form/multipart/registry/response/runtime proofs and narrow classification of infallible header parsing and streamed multipart unwrap-equivalent mutants.
 - **Proof:** the new xtask mutation command exits zero within its documented bound, covers each applicable package, emits no unexplained missed mutant, and a deliberate adjacent mutation makes it fail. `cargo run -p hemx-xtask -- test` remains green. req: test/020 req: test/021
 
 ## 3. Elect and enforce the release license policy

hemx-derive/src/lib.rs

@@ -765,9 +765,6 @@ fn add_component_register_helper(mut module: ItemMod, component: &str) -> ItemMo
     let Some(state_ty) = component_state_type(items) else {
         return module;
     };
-    if handlers.is_empty() {
-        return module;
-    }
     let calls = handlers
         .iter()
         .map(|handler| component_registration_call(handler, &component_ident));
@@ -1021,8 +1018,8 @@ mod tests {
         add_app_registry_helper, add_component_register_helper, client_handler_has_inputs,
         component_handler_names, expand_handler_function, form_contract_errors, form_decode_fields,
         form_fields, form_impl_generics, form_model_type, form_resource_id, generic_inner_type,
-        handle_params, handle_requires_form, handler_form_model_type, handler_placement,
+        handle_params, handle_requires_form, handler_arg_names, handler_form_model_type,
-        handler_syms_path, has_form_param, has_non_unit_return, is_type_named,
+        handler_placement, handler_syms_path, has_form_param, has_non_unit_return, is_type_named,
         join_contract_errors, missing_component_handlers, missing_form_generated_files_message,
         missing_handle_params, missing_handler_generated_files_message, parser_type,
         returns_result, rust_ident, syms_contains_handle, HandlerPlacement,
@@ -1461,6 +1458,14 @@ mod tests {
         assert_eq!(missing_handle_params(&path, "show", &missing), vec!["mode"]);
         assert!(missing_handle_params(&path, "unknown", &missing).is_empty());
 
+        std::fs::write(&path, "handle_param\nhandle_param\tshow\tmode\n").unwrap();
+        assert_eq!(handle_params(&path, "show"), vec!["mode"]);
+
+        let patterns: ItemFn = parse_quote! {
+            fn patterns(self, named: String, (left, right): (u8, u8), _: bool) {}
+        };
+        assert_eq!(handler_arg_names(&patterns), vec!["named"]);
+
         let _ = std::fs::remove_file(path);
     }
 
@@ -1518,6 +1523,80 @@ mod tests {
         );
         assert!(generated.contains("hemx_axum :: State"), "{generated}");
         assert!(generated.contains("state . clone"), "{generated}");
+
+        let no_components: ItemFn = parse_quote!(
+            fn registry(state: App) {}
+        );
+        assert_eq!(
+            add_app_registry_helper(no_components, vec![]).err().unwrap(),
+            "#[hemx::app] requires component registry module(s), for example #[hemx::app(todo_handlers, auth_handlers)]"
+        );
+        let unnamed_state: ItemFn = parse_quote!(
+            fn registry((state,): (App,)) {}
+        );
+        assert_eq!(
+            add_app_registry_helper(unnamed_state, vec![parse_quote!(handlers)])
+                .err()
+                .unwrap(),
+            "#[hemx::app] must be used on a registry function with a named app state argument"
+        );
+    }
+
+    #[test]
+    fn component_registration_generation_respects_existing_and_incomplete_modules() {
+        let external: syn::ItemMod = parse_quote!(
+            mod handlers;
+        );
+        let unchanged = add_component_register_helper(external.clone(), "todos");
+        assert_eq!(
+            quote!(#external).to_string(),
+            quote!(#unchanged).to_string()
+        );
+
+        for existing in ["register", "register_with_state"] {
+            let existing_ident = syn::Ident::new(existing, proc_macro2::Span::call_site());
+            let module: syn::ItemMod = parse_quote! {
+                mod handlers {
+                    struct App;
+                    #[hemx::handler]
+                    fn create(app: App) {}
+                    fn #existing_ident() {}
+                }
+            };
+            let generated = add_component_register_helper(module, "todos");
+            let items = generated.content.unwrap().1;
+            assert_eq!(items.len(), 3, "must preserve existing {existing}");
+        }
+
+        let no_state: syn::ItemMod = parse_quote! {
+            mod handlers {
+                #[hemx::handler]
+                fn create() {}
+            }
+        };
+        assert_eq!(
+            add_component_register_helper(no_state, "todos")
+                .content
+                .unwrap()
+                .1
+                .len(),
+            1
+        );
+        let no_handlers: syn::ItemMod = parse_quote! {
+            mod handlers {
+                struct App;
+                fn helper(app: App) {}
+            }
+        };
+        assert_eq!(
+            add_component_register_helper(no_handlers, "todos")
+                .content
+                .unwrap()
+                .1
+                .len(),
+            2
+        );
+        // test req: component/003 req: derive_handler/003
     }
 
     #[test]
@@ -1525,6 +1604,8 @@ mod tests {
         // req: component/003 req: derive_handler/003
         let module = parse_quote! {
             mod handlers {
+                const COMPONENT_KIND: &str = "todos";
+
                 #[hemx::handler]
                 fn sync_form(app: super::App, form: super::NewTodo) -> impl hemx::IntoEffect {
                     hemx::EventName::new("sync-form").emit("")