Function diff_gate_verdict 

pub fn diff_gate_verdict(
    base_measured: bool,
    head_measured: bool,
    violation_count: usize,
) -> &'static str

The "passed" / "failed" / "skipped" verdict for the whole [diff] gate family evaluate_diff_gate evaluates, given whether each side of the range actually measured anything.

evaluate_diff_gate only receives scalars already reduced from the base and head hotspot row sets (new_hotspot_count, delta_code_health, base_cycles/head_cycles, delta_health_ratio) — it has no way to tell “reduced from real rows, genuinely unchanged” apart from “reduced from nothing, because neither revision measured anything” (a blind ingest: a shallow checkout, or any other zero-commit ingest, leaves RevAnalyses::hotspots empty at both revisions, which zeroes every one of those scalars identically to a real no-op diff). "skipped" when base_measured and head_measured are both false — the caller passes !RevAnalyses::hotspots.is_empty() for each side. A genuinely unchanged repository with real (non-empty) hotspot rows at both revisions stays a real "passed". Mirrors change_set_gate_verdict’s verdict-string convention for the analogous ambiguity on the working-tree gate family.