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',
 ]