FIO_openDstFile() still owned the complete destination policy loop in C even
though the filesystem opener and status/action classifier were already Rust
leaves. That left confirmation, sparse-mode adjustment, overwrite removal, and
retry ordering duplicated beside private FILE* and CLI state.
Project the C-owned callbacks for diagnostics, preference mutation, user
confirmation, stdout setup, and existing-file removal. Rust now owns the
retry/order state machine and calls the existing narrow opener for each
attempt; C keeps private preferences and context, exact diagnostics, and FILE*
ownership. The callback layout is asserted on both sides, and focused tests
cover status ordering, confirmation/removal retry, setvbuf preservation, and
invalid policy inputs.
Test Plan:
- `ulimit -v 41943040; CARGO_BUILD_JOBS=1 make -j1` -- passed, including the single-thread library, MT library, and CLI binary.
- `ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo clippy --manifest-path rust/cli/Cargo.toml --all-targets -- -D warnings` -- passed.
- `ulimit -v 41943040; CARGO_BUILD_JOBS=1 cargo test --manifest-path rust/cli/Cargo.toml --all-targets` -- passed: 206 tests.
- `git diff --cached --check` -- passed.
ddidderr
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