fix(prefetch): render an unset FILETIME as "-", not 1601-01-01

[h4x0r]

Summary

prefetch4n6's filetime_to_iso had no guard for FILETIME 0, the Windows "not set" sentinel. It computed 0 / 10_000_000 - 11_644_473_600, and jiff::Timestamp::from_second accepts that value, so the function returned Some("1601-01-01T00:00:00Z") instead of None — an absent timestamp rendered as a real-looking date. Returning None lets print_record's existing - fallback engage, matching how memory-forensic's format_filetime renders the same sentinel.

Scope note — this is hardening, not a live user-visible bug

prefetch-core already breaks on the first non-positive FILETIME (core/src/lib.rs:159, Some(t) if t > 0 => push, _ => break), so ExecutionRecord.last_run_filetimes never carries a 0 for a record parsed by this workspace, and the CLI's own call site could not reach the bad rendering today. Verified empirically: a synthetic SCCA v30 with all eight last-run FILETIMEs zeroed yields last_run_times = [].

The fix still stands on its own — ExecutionRecord's fields are public, so a consumer can construct one directly, and the conversion should be correct without resting on an upstream invariant the call site does not state.

Testability seam

Added a #[cfg(test)] mod tests inside the bin rather than promoting filetime_to_iso into the library. It mirrors the convention already in forensic/src/lib.rs:196 (same #[allow(clippy::unwrap_used, clippy::expect_used)] attribute), keeps the diff minimal, and avoids adding published API surface to prefetch-forensic for a CLI-only rendering helper. The coverage gate is cargo llvm-cov --workspace --lib, so bin code sits outside the denominator either way.

TDD

Two commits, RED then GREEN.

RED (bc0f60f) — tests::unset_filetime_has_no_rendering fails:

thread 'tests::unset_filetime_has_no_rendering' panicked at forensic/src/bin/prefetch4n6.rs:86:9:
assertion `left == right` failed
  left: Some("1601-01-01T00:00:00Z")
 right: None

GREEN (935077f) — both bin tests pass.

Pre-push gate

cargo build, cargo test (17 passed, 0 failed), cargo clippy --all-targets -- -D warnings, cargo fmt --check — all clean.

Deliberately out of scope

Non-zero pre-epoch / negative FILETIMEs still convert to a pre-1970 date. memory-forensic renders those as pre-1970 (0x…); prefetch-core's t > 0 filter means they cannot arrive through the parse path here either. Left alone to keep the change minimal.

🤖 Generated with Claude Code