chore(apple-fs): audit + fix cross-platform compile hazards (XPL-1)

[oferchen]

Summary

Proactive cross-platform audit (XPL-1) of crates/apple-fs/ per the standing rule: audit the test tree for known cross-platform CI hazards before pushing, do not wait for CI to fail.

Walked every file in the crate checking the four known hazard categories enumerated in CI history:

1. #[cfg(unix)] / #[cfg(target_os = \"macos\")] gate scope - if every test in a module is gated, the whole module should be gated instead.
2. Imports above a cfg gate used only inside it (would trigger unused_imports on the off-platform).
3. let mut bindings mutated only inside a cfg block (would trigger unused_mut on the off-platform).
4. Rustdoc intra-doc links that fail to resolve when the referent is re-exported through lib.rs.

Files inspected

• crates/apple-fs/Cargo.toml
• crates/apple-fs/README.md
• crates/apple-fs/src/lib.rs
• crates/apple-fs/src/apple_double.rs
• crates/apple-fs/src/resource_fork.rs
• crates/apple-fs/tests/apple_double_round_trip.rs

6 files audited.

Findings

Rust sources: clean

• src/lib.rs - test module mixes cross-platform tests (normalize_filename_ascii_unchanged, is_apple_double_name_*, apple_double_companion_*) with #[cfg(unix)] and #[cfg(target_os = \"macos\")] gated tests. The mixed-platform composition means per-test gating is the right unit; whole-module gating would over-rotate. Helper-import use super::*; is exercised on every platform because at least one test on each platform consumes a super item. unique_path helper and its imports (env, fs, SystemTime, UNIX_EPOCH) are correctly #[cfg(unix)]-gated together.
• src/apple_double.rs - pure-data module, no cfg gates, no platform-specific surface.
• src/resource_fork.rs - matched #[cfg(target_os = \"macos\")] / #[cfg(not(target_os = \"macos\"))] pairs for every accessor; test module has at least one platform-specific test for each side, and the shared use std::path::PathBuf; is consumed on both branches (dummy_path on non-macOS, make_temp_file on macOS), so no unused_imports window.
• tests/apple_double_round_trip.rs - top-level imports (AppleDouble, EntryId) consumed by both cross-platform tests and the macOS-gated test; helper functions referenced on every platform; the macOS-only test's use apple_fs::... / use std::io; are scoped inside the gated function so they vanish cleanly on non-macOS.
• No rustdoc intra-doc links route through a lib.rs re-export - every [Type] link resolves inside its source module (io::* against use std::io;, EntryId / FINDER_INFO_LEN as siblings of their referrers).

Hygiene fix applied

• crates/apple-fs/Cargo.toml: nix = { workspace = true, features = [\"fs\"] } was declared in the unconditional [dependencies] block. nix 0.31 carries #![cfg(unix)] so it compiles to an empty crate on Windows, but the per-crate convention used by core/Cargo.toml and platform/Cargo.toml is to put nix under [target.'cfg(unix)'.dependencies]. Moved the declaration to match that convention and added a short comment explaining the rationale. Makes cross-platform intent explicit at the manifest level and aligns the crate with the rest of the workspace.

Cross-platform compile review (mental walkthrough)

• macOS: unchanged - nix still pulled in via the cfg(unix) target spec; xattr and unicode-normalization continue to flow through cfg(target_os = \"macos\").
• Linux (gnu + musl): unchanged - nix still pulled in via cfg(unix); the macOS-only deps stay absent.
• Windows: nix is now formally absent from the dep graph (previously inert via its own #![cfg(unix)]). Zero behaviour change, manifest is now consistent with core and platform.

Recommended follow-ups

None. The audit recommends no XPL-1.a / XPL-1.b follow-ups for apple-fs. The crate is small, well-gated, and benefited from the recent CCL apple-fs cleanup (#4654 era). The remaining XPL-2 / XPL-3 / XPL-4 tasks already cover the other audit targets (kqueue_stub, transfer crate, ongoing macOS/Windows CI flakiness).

Test plan

• CI: fmt + clippy on stable
• CI: nextest on stable (Linux)
• CI: Windows stable
• CI: macOS stable
• CI: Linux musl stable