feat: execute readonly type-valued compile-time slices

TODO.md

@@ -50,6 +50,9 @@ optional type-valued storage preserves nested presence, owned metadata payloads,
 checked unwraps and immutable captures across compile-time procedure boundaries.
 fallible type-valued channels own their active payloads, propagate checked errors,
 and select generated storage through `try`/`catch` and scoped cleanup.
+readonly type-valued slices own nested metadata leaves across compile-time calls,
+checked immutable-array/slice views, by-value iteration and erased arguments;
+mutable metadata borrowing remains open.
 `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
@@ -161,6 +164,7 @@ test discovery and FFI remain outside these completed slices.
   - [x] uninitialized type-record checkpoint: compile-time records/tuples containing type values start with `undefined` and fill through nested field/index updates or whole-value replacement. persistent snapshots preserve independent partial copies; defaults do not initialize undefined fields. initialized leaves and empty shapes work while premature type/value reads and incomplete procedure arguments/results diagnose read-before-initialization. fully initialized results supply erased generic inputs, generated storage/defaults and cached nominal types through interpreter/native execution. ordinary mutability/schema validation and shared per-field/cell construction bounds remain checked; general type-valued execution and broader materialization remain open.
   - [x] optional type-storage checkpoint: `?type` and optional type-valued records/arrays use owned compile-time snapshots, including nested `some!(null)`, contextual payload construction, mutable whole-value/field/index replacement, immutable if/while/conditional captures, null comparisons and checked unwraps. constant-input procedures and erased generic arguments preserve specialization-cache identity and nominal leaves while generating runtime storage through interpreter/native execution. undefined presence, incomplete payloads, non-type values, capture mutation and runtime dependencies retain diagnostics. imported private nominal types, session/source disposal and repeat compilation preserve ownership. fallible type-valued channels are covered below; general type-valued execution and broader constant materialization remain open.
   - [x] fallible type-storage checkpoint: explicit success/error channels containing types use owned compile-time snapshots, including nested optional/record/array payloads, whole-value updates, independent copies, constant-input procedures and erased generic inputs. `try` validates error subsets and propagates through enclosing producers; `catch` binds immutable exact error payloads and selects generated types or runtime handlers. composed metadata errors preserve named variants, nominal leaves and cache identity. returned snapshots precede scoped LIFO `defer`/`errdefer` cleanup; fallible `void` supports bare returns and successful fallthrough. incomplete/uninitialized channels, invalid payloads/compositions, capture mutation and runtime dependencies retain diagnostics. imported private types, source/session disposal and repeat compilation preserve ownership through interpreter/native execution. runtime metadata storage, general type-valued execution and broader materialization remain open.
+  - [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.
   - [ ] 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.