slovo/.llm/BETA_16_STRING_SCANNING_AND_TOKEN_BOUNDARY_FOUNDATION.md

1.0.0-beta.16 String Scanning And Token Boundary Foundation

Status: combined Slovo/Glagol release scope for 1.0.0-beta.16.

1.0.0-beta.16 adds the first explicit string scanning and token-boundary source facades to std.string: byte access, substring extraction, and prefix/suffix checks over the current runtime string representation. The release also promotes the matching compiler-known runtime names through the C runtime, LLVM lowering, source fallback evaluator, diagnostics inventory, local facade fixtures, and release-gate coverage.

Scope

• Add byte_at_result ((value string) (index i32)) -> (result i32 i32) to lib/std/string.slo.
• Add slice_result ((value string) (start i32) (count i32)) -> (result string i32) to lib/std/string.slo.
• Add starts_with ((value string) (prefix string)) -> bool to lib/std/string.slo.
• Add ends_with ((value string) (suffix string)) -> bool to lib/std/string.slo.
• Mirror those source facades in examples/projects/std-layout-local-string/src/string.slo.
• Extend the local and explicit std.string examples with success and ordinary failure checks for the four helpers.
• Promote matching Glagol runtime entries for std.string.byte_at_result, std.string.slice_result, std.string.starts_with, and std.string.ends_with.
• Add LLVM declarations and lowering for the four promoted runtime names.
• Add C runtime implementations for byte access, byte slicing, prefix checks, and suffix checks.
• Extend the source fallback test runner behavior for those names.
• Add focused beta16 compiler coverage for lowering, hosted runtime execution, and source fallback execution.
• Extend diagnostics snapshots for arity, type, context, shadowing, and richer unsupported string-scanning names.
• Extend standard-library source-search and local-facade fixtures plus promotion-gate inventory alignment.
• Update README, lib/std/README.md, post-beta roadmap, language roadmap, release notes, v1 spec, generated stdlib API, compiler docs, release gate, and standard-runtime catalog for beta16.

Contract

• Helpers are byte-oriented over bytes before the trailing NUL in current runtime strings.
• byte_at_result returns ok byte for a valid zero-based byte index and err 1 for invalid indexes.
• slice_result returns ok text for a valid byte range and err 1 for invalid ranges.
• slice_result allocation failure may follow the existing string allocation trap policy.
• starts_with and ends_with perform byte prefix/suffix checks; empty prefix and suffix match.

Explicit Non-Scope

• no Unicode scalar, grapheme, display-width, locale, normalization, or case-folding promise
• no JSON parser
• no object or array parser
• no tokenizer/scanner object API
• no language slice/view syntax or borrowed substring view
• no mutable strings or string containers
• no stable stdlib/API freeze
• no stable ABI/layout or ownership guarantee for returned string allocations
• no performance claim
• no maps, sets, generic collections, or recursive JSON value support
• no worker-owned commit, tag, push, or publication before controller gates

Expected Verification

• cargo fmt --check
• cargo test --test standard_string_scanning_beta16
• cargo test --test diagnostics_contract
• cargo test --test standard_string_source_fallback_helpers_alpha
• cargo test --test standard_core_facade_source_search_alpha
• cargo test --test string_runtime
• cargo test --test promotion_gate -- --ignored
• cargo test
• git diff --check
• stale current-stage scan for 1.0.0-beta.15
• public-text scan for local usernames, local filesystem paths, and private host publication references
• final ./scripts/release-gate.sh after commit and generated catalog sync