Close the two gaps the minimal TY4c goldens did not exercise:

- Transitive trait-field contribution: a `trait` may itself `composes`
  other field-bearing traits, and those fields flow to every type that
  composes it (`record User composes Entity`, `trait Entity composes
  Identified` -> `u.id`). N1 records a trait's own composes head names
  (Interner::trait_composed_traits); field_access::trait_contributed_field
  is the one cycle-guarded recursive walk that both the read surface
  (concrete + `where E is Error` bound Var receiver) and the E0727
  collision check call.

- data auto-derive (tag-then-payload): `data .. composes Equals`/`Hash`
  registers a derived coherence row for the parent type (duplicate user
  impl -> E0709) and fires E0711 when a variant payload slot (named or
  positional) is not itself derivable. Payload types are lifted from the
  CST at check-time; emit_if_underivable phrases the same E0711 for a
  record field and a data payload.

New goldens (multi-page, trap-covered): transitive_trait_fields.cktest,
data_auto_derive.cktest. Doc: TY4 "What landed after TY4c".

@@ -699,0 +680,4 @@
+fn runtime_coverage_is_exhaustive() {
+    let apps = corpus_apps();
+    let tested: BTreeSet<&str> = RUNTIME_TESTED.iter().copied().collect();
+    let mut failures = Vec::new();

@@ -14,0 +41,4 @@
+    /// traits). Empty when the trait composes nothing. Same shared `composes`
+    /// projection a `record` / `data` head reads; N1 records these names (not
+    /// `TraitId`s) and `TY4c` resolves them against module scope.
+    pub fn composed_traits(&self) -> impl Iterator<Item = NameToken> + 'a {

@@ -258,0 +256,4 @@
+/// Subtrees whose own span does not contain `target` are pruned. Shared with
+/// the body walker's [`let`-annotation reader](crate::check) (TY6), which
+/// finds a `LetStmt` CST node by its lowered `Stmt.span`.
+pub(crate) fn find_node_with_span(