[e54-bot]

What changed

wright update re-implemented download, size-limit, checksum, and staging logic that wright-driver::store already provides for provider and lint-package downloads. This routes the update path through the shared helpers:

• store::client(USER_AGENT) replaces the local update_client builder (same user agent, same 60 s timeout).
• store::read_limited(response, MAX_DOWNLOAD_BYTES) replaces the .take(128 MiB).read_to_end copy. Per the owner decision, an over-limit body now surfaces the existing OverLimit diagnostic — download from {url} exceeds the 128 MiB size limit — instead of a silent truncation that later failed as a checksum mismatch.
• store::verify_sha256 is now the single SHA-256 checksum verification in the workspace (ChecksumError::{Empty, Invalid, Mismatch}). Both opy_provider and update delegate to it and keep their caller-specific diagnostic wording.
• store::reserve_staging_dir replaces the local staging-dir builder, adding collision retries.
• wright_driver::store is now pub so wright-cli can use the helpers; items that remain internal (wright_data_base, promote_dir, PromoteError) stayed pub(crate).

Test layout: tests/update/main.rs was already over the size-guard line limit, so the provider tests moved to tests/update/provider.rs (new [[test]] target) and the shared fixtures to tests/update/support.rs. Added an_archive_over_the_size_limit_fails_with_a_limit_error, which serves a 128 MiB + 1 archive from the mock server and asserts exit 4, the size-limit wording, no checksum wording, and an unchanged binary.

Verified

• cargo test -p wright-cli --test update --test update_provider — 31/31 pass, including the new over-limit test.
• cargo test -p wright-cli --bin wright — 80/80 unit tests pass.
• cargo test -p wright-driver --lib — 101/101 pass.
• cargo test -p wright-driver --test lint_package_store -p wright-cli --test lint_package — pass.
• cargo fmt --all -- --check, cargo clippy --workspace --all-targets --all-features -- -D warnings, git diff --check — clean.

Unverified

• Windows/macOS update paths were exercised by the existing Linux-hosted tests via env overrides only (WRIGHT_INSTALL_OS), same as before.

Fixes #1007

[Teakowa]

LGTM after independent review.