mizan-axum + macros: state threading, array/map lowering, merge shape semantics

Three substrate extensions surfaced by the Blazr session port:

1. **App-state threading.** mizan-axum::router() is now generic over a
   user-supplied state type and threads `Arc<dyn Any + Send + Sync>` into
   every dispatch via RequestHandle. Handlers downcast to their concrete
   AppState. The stateless AFI fixture uses `router_stateless()` (matches
   the prior signature). RequestHandle gains a `from_dyn()` constructor
   to wrap already-erased trait-object references.

2. **`[T; N]` and `BTreeMap<K, V>` lowering in #[derive(Mizan)].** Fixed
   arrays emit as `List<T>` (matches Python `tuple[float,...]` → JSON
   array). String-keyed maps emit as `List<V>` — closest approximation
   until KDL grows a `dict` shape. Also: vec-element registrations get a
   per-function scope suffix so two handlers returning `Vec<Same>` don't
   collide at the static-name layer.

3. **`types_match` for merge: upsert-into-list semantics.** Now matches
   Python `types_match_for_merge`: direct (T == T), upsert (slot is
   `Alias(List(T))`, value is T), and list-replace (both sides list).
   The AFI fixture only exercised the direct path; the Blazr port's
   `morph_set_value` returning a single `MorphLayer` into a context with
   `Vec<MorphLayer>` slot is what surfaced the gap.

AFI codegen + wire parity stays 12/12 green after these substrate changes.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

cores/mizan-rust-macros/src/function.rs

@@ -240,7 +240,11 @@ pub fn expand(args: FunctionArgs, item: ItemFn) -> TokenStream {
         });
         // Also register the element type itself by its own name. `TYPE_NAME`
         // is an associated const, so this is usable in a static initializer.
-        let elem_static = element_type_static_ident(elem);
+        // The static ident scopes by the function name so two handlers
+        // returning `Vec<Same>` don't collide; the IrSnapshot's BTreeMap
+        // dedupes by the entry's `name` at emit time.
+        let elem_static =
+            element_type_static_ident_scoped(elem, &fn_name.to_shouty_snake_case());
         type_registrations.push(quote! {
             #[::mizan_core::__priv::linkme::distributed_slice(::mizan_core::TYPES)]
             #[linkme(crate = ::mizan_core::__priv::linkme)]
@@ -481,14 +485,16 @@ fn build_dispatch(
     }
 }
 
-fn element_type_static_ident(ty: &Type) -> syn::Ident {
-    // Derive a unique static-name for the type's registration entry. Uses
-    // the last path segment's identifier as the discriminator.
+fn element_type_static_ident_scoped(ty: &Type, fn_scope: &str) -> syn::Ident {
+    // Derive a unique static-name for the type's registration entry,
+    // scoped by the surrounding function so siblings returning the same
+    // `Vec<T>` don't collide at the static-name layer. The IR-side
+    // BTreeMap dedupes by TypeEntry.name at emission time.
     let last = match ty {
         Type::Path(tp) => tp.path.segments.last().map(|s| s.ident.to_string()),
         _ => None,
     };
     let suffix = last.unwrap_or_else(|| "ANON".to_string()).to_shouty_snake_case();
-    format_ident!("__MIZAN_TYPE_ELEM_{}", suffix)
+    format_ident!("__MIZAN_TYPE_ELEM_{}_FOR_{}", suffix, fn_scope)
 }
 

cores/mizan-rust-macros/src/shape.rs

@@ -56,12 +56,68 @@ pub fn type_shape_expr(ty: &Type) -> TokenStream {
             ::mizan_core::TypeShape::List(::std::boxed::Box::new(#inner_shape))
         };
     }
+    if let Some(elem) = unwrap_array(ty) {
+        // `[T; N]` lowers to `list { T }` on the wire — JSON arrays don't
+        // carry length, so the IR contract is the same as `Vec<T>`.
+        let inner_shape = type_shape_expr(&elem);
+        return quote! {
+            ::mizan_core::TypeShape::List(::std::boxed::Box::new(#inner_shape))
+        };
+    }
+    if let Some(elem) = unwrap_btreemap_value(ty) {
+        // `BTreeMap<K, V>` on the wire is a JSON object keyed by `K`'s
+        // string form. The Mizan IR doesn't model dynamic-keyed maps as a
+        // distinct shape — closest equivalent is a list of value entries.
+        let inner_shape = type_shape_expr(&elem);
+        return quote! {
+            ::mizan_core::TypeShape::List(::std::boxed::Box::new(#inner_shape))
+        };
+    }
     if let Some(p) = primitive_of(ty) {
         return quote! { ::mizan_core::TypeShape::Primitive(#p) };
     }
     // Fallback: assume a user-defined struct/enum implementing MizanType.
-    // The Ref name comes from `<T as MizanType>::type_name()` at runtime.
-    quote! { ::mizan_core::TypeShape::Ref(<#ty as ::mizan_core::MizanType>::type_name()) }
+    // The Ref name comes from `<T as MizanType>::TYPE_NAME` (associated const).
+    quote! { ::mizan_core::TypeShape::Ref(<#ty as ::mizan_core::MizanType>::TYPE_NAME) }
+}
+
+/// If `ty` is `[T; N]`, return `T`. Otherwise None.
+pub fn unwrap_array(ty: &Type) -> Option<Type> {
+    if let Type::Array(a) = ty {
+        Some((*a.elem).clone())
+    } else {
+        None
+    }
+}
+
+/// If `ty` is `BTreeMap<K, V>` or `HashMap<K, V>`, return `V` (the value).
+/// String-keyed maps land on the wire as JSON objects; the IR carries the
+/// value shape as a list element since KDL doesn't model dynamic-keyed maps
+/// distinctly yet.
+pub fn unwrap_btreemap_value(ty: &Type) -> Option<Type> {
+    let path = match ty {
+        Type::Path(TypePath { qself: None, path }) => path,
+        _ => return None,
+    };
+    let last = path.segments.last()?;
+    let name = last.ident.to_string();
+    if name != "BTreeMap" && name != "HashMap" {
+        return None;
+    }
+    let args = match &last.arguments {
+        PathArguments::AngleBracketed(a) => a,
+        _ => return None,
+    };
+    // BTreeMap<K, V> — second type argument is V.
+    let mut type_args = args.args.iter().filter_map(|a| {
+        if let GenericArgument::Type(t) = a {
+            Some(t.clone())
+        } else {
+            None
+        }
+    });
+    type_args.next()?; // skip K
+    type_args.next()
 }
 
 /// Emit a `Primitive` const-expression for `ty`, or `None` if `ty` isn't a

cores/mizan-rust/src/graph_check.rs

@@ -16,9 +16,29 @@ pub(crate) fn resolve_type_shape(name: &str) -> Option<NamedType> {
     None
 }
 
-/// Structural equality on named types. Two types are merge-compatible iff
-/// they have identical shape — matches Python's `types_match_for_merge`.
-pub(crate) fn types_match(a: &NamedType, b: &NamedType) -> bool {
+/// Merge-compatibility on named types. A mutation return `value` can
+/// splice into a context slot `slot` when any of three shapes hold —
+/// matches Python's `types_match_for_merge`:
+///   * direct: `slot` shape equals `value` shape → replace
+///   * upsert: `slot` is `list[T]`, `value` is `T` → upsert by id
+///   * list-replace: `slot` is `list[T]`, `value` is `list[T]`
+///
+/// The first argument is the slot (context member's output type); the
+/// second is the value (mutation's output type).
+pub(crate) fn types_match(slot: &NamedType, value: &NamedType) -> bool {
+    if named_shapes_equal(slot, value) {
+        return true;
+    }
+    // Upsert: slot is `Alias(List(T))`, value is `T`-shaped.
+    if let NamedType::Alias(TypeShape::List(elem)) = slot {
+        if shape_matches_named(elem, value) {
+            return true;
+        }
+    }
+    false
+}
+
+fn named_shapes_equal(a: &NamedType, b: &NamedType) -> bool {
     match (a, b) {
         (NamedType::Struct(fa), NamedType::Struct(fb)) => fields_match(fa, fb),
         (NamedType::Alias(sa), NamedType::Alias(sb)) => shapes_match(sa, sb),
@@ -27,6 +47,21 @@ pub(crate) fn types_match(a: &NamedType, b: &NamedType) -> bool {
     }
 }
 
+/// True when a `TypeShape` (the slot's list-element) describes the same
+/// shape as a `NamedType` (the mutation's full output).
+fn shape_matches_named(shape: &TypeShape, named: &NamedType) -> bool {
+    match shape {
+        TypeShape::Ref(name) => {
+            if let Some(referenced) = resolve_type_shape(name) {
+                named_shapes_equal(&referenced, named)
+            } else {
+                false
+            }
+        }
+        _ => false,
+    }
+}
+
 fn fields_match(a: &[StructField], b: &[StructField]) -> bool {
     if a.len() != b.len() {
         return false;

cores/mizan-rust/src/runtime.rs

@@ -17,10 +17,18 @@ pub struct RequestHandle<'a> {
 }
 
 impl<'a> RequestHandle<'a> {
+    /// Wrap a typed reference. The most common path — handlers downcast back
+    /// to `T` via `downcast::<T>()`.
     pub fn new<T: Any + Send + Sync>(req: &'a T) -> Self {
         Self { inner: req }
     }
 
+    /// Wrap an already-erased `dyn Any` reference. Used by HTTP adapters
+    /// that thread an `Arc<dyn Any + Send + Sync>` app state in.
+    pub fn from_dyn(req: &'a (dyn Any + Send + Sync)) -> Self {
+        Self { inner: req }
+    }
+
     pub fn downcast<T: Any + Send + Sync>(&self) -> Option<&'a T> {
         self.inner.downcast_ref::<T>()
     }