pub fn effective_range_base(root: &Path) -> Result<String>Expand description
Effective diff-range base (git-native-v2 D1): the live merge-base of the local default branch with HEAD, the single entry point for all range semantics (locked-rule gate, specs landing, change diff/commit count, staleness). Computing it on demand means the range always covers exactly the branch’s own work and shrinks automatically after merge/rebase — no stored state, immune to unpushed accumulation. Fails when git is unavailable or no default ref exists; callers fall back to the stored base_sha (fail-open, same as the pre-v2 behavior).