feat: execute explicitly annotated compile-time metadata locals

TODO.md

@@ -58,6 +58,8 @@ checked immutable-array/slice views, by-value iteration and erased arguments;
 mutable metadata borrowing remains open.
 ordinary metadata-input procedures also compute owned runtime values, including
 reflected field names/counts, recursive helpers and fallible cleanup.
+explicitly annotated local metadata storage also makes ordinary procedures
+constant-input producers, preserving owned updates, loops, recursion and cleanup.
 `field!` selects record/tuple/enum and sequence members using compile-time names,
 including runtime places and type-control updates without runtime reflection.
 `struct_type!` generates ordinary/C-layout records from constant name/type/default
@@ -172,6 +174,7 @@ test discovery and FFI remain outside these completed slices.
   - [x] readonly type-slice checkpoint: `[]type` and slices of type-valued records/arrays use owned compile-time snapshots. contextual literals, immutable readonly array views, nested slice views, checked `usize` bounds/indexing, `.len`, empty shapes and ordinary/inline by-value iteration preserve exact nominal leaves. constant-input procedure parameters/results, erased generic inputs, optional/fallible nesting and normalized cache keys generate runtime storage/defaults through interpreter/native execution. mutable annotations/backing, metadata sentinels, invalid ranges/indices, readonly writes, incomplete leaves and runtime dependencies retain diagnostics. imported private types, source/session disposal, shared construction bounds and repeat compilation preserve ownership. mutable metadata borrowing, runtime metadata storage, general type-valued execution and broader constant materialization remain open.
   - [x] tagged type-storage checkpoint: tagged unions containing type leaves own active payload snapshots through typed/contextual construction, direct and nested field/index updates, immutable by-value matches and whole-value variant replacement. constant-input procedure arguments/results, erased generic inputs and normalized cache keys preserve nominal leaves and saved copies while generating runtime storage/defaults through interpreter/native execution. undefined union locals and nested record/array storage require whole-value initialization; inactive reads/writes, malformed explicit tags, nominal initializer conflicts, readonly updates, incomplete results and narrow overflow retain diagnostics. explicit sparse tag enums may contain unused members without adding match cases. imported private types, source/session disposal and repeat compilation preserve ownership. untagged metadata layouts remain invalid; mutable metadata borrowing, runtime metadata storage, general type-valued execution and broader constant materialization remain open.
   - [x] metadata-input execution checkpoint: procedures with ordinary type-valued parameters execute entirely at compile time even when returning runtime-representable values. all inputs remain explicit constants; owned scalar/record/array/string results, recursive readonly metadata iteration, reflected field names/counts and private nominal leaves work through interpreter/native execution. plain/fallible `void` retain bare-return/fallthrough semantics; ordinary fallible results propagate through `try`/`catch` and run scoped `defer`/`errdefer`. runtime dependencies and incomplete payloads retain diagnostics; source/session disposal and repeat compilation preserve ownership. dependent signature parameters still require `$`; general type-valued execution, mutable metadata borrowing and broader constant materialization remain open.
+  - [x] explicit metadata-local execution checkpoint: procedures with explicitly annotated type-valued locals execute entirely at compile time without metadata inputs or results. scalar inputs remain explicit constants; nested metadata records/arrays, undefined initialization, owned copies, checked field/index updates, loops, captures, recursion and scoped fallible cleanup reuse existing type-control execution through interpreter/native paths. runtime inputs and uninitialized leaves diagnose; ordinary unannotated local type aliases retain runtime parameters. imported private nominal leaves, source/session disposal and repeat compilation preserve ownership. inferred metadata-only locals, mixed runtime/type-valued execution, mutable metadata borrowing and broader constant materialization remain open.
   - [ ] remaining gate: general type-valued compile-time execution, broader constant materialization (including address-bearing untagged unions, nonnull data pointers and mutable slices), plus remaining existing-library acceptance for broader `meta` operations and `io.print`. formatting parsing and broader imported C-binding support may interleave with later gates.
 - [ ] remaining source constructs: multiline strings. boolean and optional-capture conditional expressions, yielding value blocks, `yield`, compound updates and bitwise operators are covered above. examples: `source/parser/parse.hon`, `source/llvm/runtime.hon`.
 - [ ] standard-library milestone: compile/run a multi-package program exercising existing allocation and IO, including error cleanup; no replacement miniature standard library.