default struct fields

TODO.md

@@ -731,8 +731,8 @@
   - enabled `&<array literal>` (Zig's `&.{...}`): the literal is promoted to an
     anonymous global whose address decays to a slice, so list fields like
     `libraries = &["raylib"]` work; empty lists are `&[]`
-  - deferred: build graph / steps / caching, multiple artifacts, computed paths
-    (needs string building), struct field defaults to drop `&[]` on empty lists
+  - deferred: build graph / steps / caching, multiple artifacts, and computed paths
+    (needs string building); milestone 44 later removed explicit `&[]` build-config fields
 
 29. fix bugs (implemented)
   - bare `return` is the empty return for void functions; `yield` always requires a
@@ -925,7 +925,14 @@
   - runtime pointer contexts implicitly materialize a bare identity; pointer-to-identity conversion is
     rejected, and bare-containing aggregates cannot enter runtime storage or ABI/C layouts
 
-44. struct field defaults on declaration
+44. struct field defaults on declaration (implemented)
+  - named native structs accept `field T = expression`; keyed construction evaluates defaults
+    for omitted fields while explicit initializers override them
+  - defaults resolve names in the declaration file, participate in record constraint inference,
+    and work during runtime and comptime construction
+  - `@std/build.BuildConfig` uses defaults for optional list fields
+  - fields without defaults remain required; C-layout records, unions, tuples, and anonymous
+    generated structs do not accept defaults
 
 ## A word on unchecked casts