Align validator identity and span domain checks

docs/internal/validators.md

@@ -23,7 +23,8 @@ Deterministic:
 - `proposal_shape`
 - `confidence_threshold`
 - `original_text_presence`
-- `non_empty_corrected_text`
+- `non_empty_resulting_segment` — rejects edits that would leave the segment
+  blank, regardless of replacement-span length.
 - `no_effect`
 - `protected_terms`