rust-abstraction-designlisted

## Outcome Produce the least powerful Rust abstraction that satisfies demonstrated reuse, substitution, extension, lifetime, and failure requirements while keeping behavior understandable and safe. ## Compatibility Portable across Claude Code, Codex, and OpenCode. Honor the target repository's Rust toolchain, edition, MSRV, dependency versions, public API policy, object-safety requirements, and unsafe-code rules. Edition 2024 examples require Rust 1.85 or newer. Optional network research requires authorization; without it, qualify version-sensitive claims. Native-client compatibility remains unverified without a dated exact-SHA report. ## Inputs - Concrete use cases, callers, implementations, extension expectations, and performance constraints. - Existing types, traits, generic bounds, lifetimes, errors, panics, unsafe blocks, and tests. - Public API and compatibility commitments plus repository lint and dependency policy. - Whether implementation families are closed, open, compile-time selected, or runtime selected. ## Safety - Keep code concrete until reuse or variation pressure is demonstrated; do not introduce traits, generics, macros, or code generation speculatively. - Treat public traits, generic bounds, auto traits, error variants, and lifetimes as compatibility contracts. Avoid broad changes without migration evidence. - Keep required `unsafe` operations minimal, document invariants and `# Safety`, and expose a safe API only when those invariants can be