# 1.0.0-beta.20 String Search And ASCII Trim Foundation

## Scope

`1.0.0-beta.20` is a standard-library and compiler-gate slice. It does not
change source-language syntax, runtime C, compiler-known runtime names, or
ABI/layout policy.

The release adds source-authored `std.string` helpers:

- `contains ((value string) (needle string)) -> bool`
- `index_of_option ((value string) (needle string)) -> (option i32)`
- `last_index_of_option ((value string) (needle string)) -> (option i32)`
- `trim_ascii_start ((value string)) -> string`
- `trim_ascii_end ((value string)) -> string`
- `trim_ascii ((value string)) -> string`

## Contract

Search is byte-oriented over the current runtime string representation.
`index_of_option` returns the first zero-based byte offset for a matching
needle, `last_index_of_option` returns the last zero-based byte offset, and
`contains` is true when `index_of_option` returns `some`.

Empty needles are valid:

- `index_of_option value ""` returns `some 0`
- `last_index_of_option value ""` returns `some (len value)`
- `contains value ""` returns `true`

Missing needles return `none`.

ASCII trim removes only these byte values from the requested edges:

- `9` horizontal tab
- `10` line feed
- `11` vertical tab
- `12` form feed
- `13` carriage return
- `32` space

The helpers compose over already-promoted string primitives:

- `std.string.len`
- `std.string.byte_at_result`
- `std.string.slice_result`
- `std.string.starts_with`
- `std.string.ends_with`

## Non-Scope

This scope does not add:

- compiler-known `std.string.*` runtime names for the new helpers
- runtime C helper implementations
- source-language syntax
- Unicode scalar, grapheme, display-width, or normalization semantics
- case folding or locale-sensitive search
- regular expressions
- tokenizer/parser APIs
- mutable strings
- language slice/view syntax
- stable string ABI/layout
- stable allocation ownership rules
- stable standard-library compatibility
- performance claims

## Acceptance Criteria

- `lib/std/string.slo` exports all six helpers.
- Explicit `std.string` import examples exercise contains, first/last search,
  missing needles, empty needles, leading trim, trailing trim, full trim,
  all-whitespace trim, and no-trim cases.
- Local `std-layout-local-string` examples mirror the public helper surface.
- Focused compiler coverage verifies the helpers are source-authored and that
  direct compiler-known runtime calls for the new names remain unsupported.
- `scripts/release-gate.sh` runs the focused beta20 test.
- Generated standard-library API documentation includes the new signatures.

## Gates

```bash
cargo fmt --check
cargo test --test standard_string_search_trim_beta20
cargo test --test standard_string_source_fallback_helpers_alpha
cargo test --test standard_string_scanning_beta16
cargo test
./scripts/release-gate.sh
```