feat: execute collection and index iteration

TODO.md

@@ -27,8 +27,11 @@ including owned by-value tagged payload captures in ordinary generic procedures.
 type-producing procedures also accept ordinary
 constant inputs, cached and erased like explicit compile-time arguments. mutable
 type/value locals, direct and aggregate field/index assignments, branches,
-scalar/enum/tagged-union matching and bounded integer-range/while loops now generate types and storage. optional
+scalar/enum/tagged-union matching and bounded integer-range/collection/while loops now generate types and storage. optional
 if/while captures and tagged payload matches select nested constructors, lengths, signatures and defaults;
+array/slice/string/pointer-to-array collection loops support exact copy/pointer
+captures and `usize` indices through both paths; type-producing bodies iterate
+materializable arrays/strings by value without retaining interpreter addresses.
 general type-valued execution, reflection and generic library acceptance remain open.
 the driver retains frontend storage and source provenance through
 `@source/compilation`, with compilation-wide AST node identities.
@@ -79,8 +82,9 @@ test discovery and FFI remain outside these completed slices.
   - [x] generic match-specialization checkpoint: side-effect-free constant scalar/enum/tagged-union subjects in concrete generic procedures and explicit `match $(subject)` expressions/statements select an arm before body specialization/checking. reuse ordinary checked IR for pattern types, ranges, overlap, exhaustiveness and every arm's capture validation; only the selected body is elaborated. exact by-value payload types/owned strings, runtime parameters, nested expression matches, cleanup, return/loop transfers, imported producers and repeatable compilation work through interpreter/native execution. ordinary call/runtime/mutable subjects stay runtime; contextual aggregates with possible runtime defaults are not implicitly evaluated. all bodies remain parsed/name-resolved; storage-bearing payloads retain the constant-materialization escape boundary.
   - [x] optional type-control checkpoint: type-producing bodies execute optional if/while guards with immutable by-value payload captures. ordinary checked IR validates guards; selected scalar/aggregate payloads retain exact types and owned strings across nested captures, generated storage/defaults, loop updates/transfers and early returns. absent optionals skip unselected bodies; invalid guards, capture mutation/shadowing, overflow and execution bounds retain diagnostics. imported producers, dependency provenance, nominal cache identity and repeatable compilation work through interpreter/native execution. null data/function pointers materialize correctly; nonnull storage-bearing payloads retain the constant-materialization escape boundary.
   - [x] aggregate type-update checkpoint: type-producing bodies update initialized, materializable aggregate locals through nested record fields and mutable fixed-array indices. ordinary checked IR validates and executes each assignment, retaining exact value types, mutability (including immutable payload captures), index types/bounds, unknown-field and narrow-overflow diagnostics. new owned constants preserve earlier by-value copies while later loops, generated storage and defaults observe updates. imported producers, dependency provenance, nominal cache identity and repeatable compilation work through interpreter/native execution. pointer/slice-backed mutation, uninitialized aggregate construction and type-valued aggregate storage remain open.
-  - [ ] remaining gate: general type-valued compile-time execution, inline match/loop expansion and reflection (`typeinfo!`, `field!`, `struct_type!`, generated type/default arrays), broader constant materialization (including untagged unions and storage-bearing values), plus existing-library acceptance. required collection/index iteration, expression-valued control flow, compound updates, formatting parsing and imported C-binding support may interleave with later gates.
-- [ ] remaining source constructs: collection/index iteration, expression-valued control flow and `yield`, compound updates and multiline strings. examples: `source/parser/parse.hon`, `source/llvm/runtime.hon`.
+  - [x] collection-iteration checkpoint: arrays, slices, strings and single pointers-to-arrays support immutable exact-type copy captures, storage-qualified pointer captures and optional `usize` indices through interpreter/native execution. iterables/bounds evaluate once, array lvalues remain borrowed and later element updates are visible; temporary arrays, aggregate copy isolation, zero-cell/empty collections, nested loops and cleanup across transfers retain ordinary semantics. ordinary constant-input procedures reuse the same checked IR; type-producing bodies iterate materializable arrays/strings with by-value captures, fixed entry-time place indices, generated storage, nominal cache identity, dependency diagnostics, shared execution bounds and repeatable compilation. storage-bearing type-control captures and type-valued elements retain their existing boundaries.
+  - [ ] remaining gate: general type-valued compile-time execution, inline match/loop expansion and reflection (`typeinfo!`, `field!`, `struct_type!`, generated type/default arrays), broader constant materialization (including untagged unions and storage-bearing values), plus existing-library acceptance. required expression-valued control flow, compound updates, formatting parsing and imported C-binding support may interleave with later gates.
+- [ ] remaining source constructs: expression-valued control flow and `yield`, compound updates and multiline strings. 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.
 - [ ] native driver integration: required C ABI declarations, `process.Init` startup arguments/IO, actual CLI exit statuses, file loading, temporary files and spawning Clang. Honey-generated programs currently accept only parameterless `main` and print its result; Bro's bootstrap startup support is not Honey backend support.
 - [ ] self-hosting proof: bootstrap-built Honey builds the production compiler (excluding test-only imports); that executable rebuilds the compiler; the rebuilt compiler passes representative interpreter/native examples and CLI/error scenarios without Bro at runtime.