fix(extract): count a singular use of a plural-defined term as a use

Mirror of the previous singular→plural fix. A term defined in the plural
("Deliverables", "Affiliates", "Parties") but used only in the singular
("each Deliverable", "an Affiliate") matched nothing, so STRUCT-005
reported it as an unused template leftover.

Add regularSingular(term) — the inverse of regularPlural — and match it too.
It is guarded by a round trip: a candidate singular is accepted only when
re-pluralizing it reproduces the exact term, so a non-plural word ending in
"s" ("Business" → "Busines" → "Businesses" ≠ "Business") is rejected and a
made-up singular of an irregular ("Analysis" → "Analysi") never matches real
text.

Zero golden churn: no fixture in the 327-doc corpus defines a term in the
plural and uses it only in the singular.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: clay-good

README.md

@@ -4,7 +4,7 @@
 
 **Vaulytica is the second pair of eyes you can cite.**
 
-`1,111 deterministic rules` · `20 cross-document checks` · `5 pre-disclosure checks` · `3 execution-readiness reconciliations` · `5 derived-deadline families` · `16 document sub-domains` · `88 state-law overlays (non-compete · security deposit · usury · will formalities)` · `10 export formats` · `0 servers` · `0 AI` · `5,859 passing tests` · `v9.41.0` · `MIT`
+`1,111 deterministic rules` · `20 cross-document checks` · `5 pre-disclosure checks` · `3 execution-readiness reconciliations` · `5 derived-deadline families` · `16 document sub-domains` · `88 state-law overlays (non-compete · security deposit · usury · will formalities)` · `10 export formats` · `0 servers` · `0 AI` · `5,860 passing tests` · `v9.41.0` · `MIT`
 
 ![Vaulytica landing page — "Drop legal docs. Get a report. Nothing leaves your browser."](docs/images/hero.png)
 
@@ -1332,7 +1332,7 @@ npm run dev          # open the printed URL
 npm run build        # static site → dist/
 npm run typecheck    # tsc --noEmit
 npm run lint         # eslint
-npm run test         # vitest — 5,859 tests, ~35s
+npm run test         # vitest — 5,860 tests, ~35s
 npm run coverage     # vitest + V8 coverage, enforces the regression floor
 npm run accuracy     # v5 Ground Truth harness → tools/accuracy/SCOREBOARD.md
 npm run mutation     # Stryker mutation score (scoped to extractors; slow, off the per-push path)

src/extract/definitions.test.ts

@@ -51,6 +51,22 @@ describe("extractDefinitions", () => {
     expect(map.entries.find((e) => e.term === "Confidential Material")?.used_at.length).toBe(1);
   });
 
+  it("counts a singular use of a plural-defined term as a use", () => {
+    // Mirror of the above: a term defined in the plural but used only in the
+    // singular ("Deliverables" … "each Deliverable"; "Affiliates" … "an
+    // Affiliate") is still used, not an unused template leftover.
+    const tree = buildTree([
+      "Definitions",
+      '"Deliverables" means the items listed in the SOW.',
+      '"Affiliates" means entities under common control.',
+      "Provider shall submit each Deliverable to any Affiliate on request.",
+      "A late Deliverable incurs a penalty.",
+    ]);
+    const map = extractDefinitions(tree);
+    expect(map.unused_terms).not.toContain("Deliverables");
+    expect(map.unused_terms).not.toContain("Affiliates");
+  });
+
   it("does not treat an unrelated word sharing a prefix as a plural use", () => {
     const tree = buildTree([
       "Definitions",

src/extract/definitions.ts

@@ -542,14 +542,14 @@ export function extractDefinitions(tree: DocumentTree): DefinitionMap {
 
   // Pass 3: record every use of each term outside its definition.
   for (const entry of definitions.values()) {
-    // Match the term as defined and its regular plural — a term defined in the
-    // singular is routinely used in the plural ("… the Confidential Materials
-    // it receives"), which is still a use, not a template leftover.
-    const plural = regularPlural(entry.term);
-    const alternatives =
-      plural && plural !== entry.term
-        ? `${escapeRegExp(entry.term)}|${escapeRegExp(plural)}`
-        : escapeRegExp(entry.term);
+    // Match the term as defined and its regular plural/singular — a term
+    // defined in one number is routinely used in the other ("Confidential
+    // Material" … "the Confidential Materials"; "Deliverables" … "each
+    // Deliverable"), which is still a use, not a template leftover.
+    const variants = [entry.term, regularPlural(entry.term), regularSingular(entry.term)].filter(
+      (v): v is string => !!v && v !== entry.term,
+    );
+    const alternatives = [entry.term, ...new Set(variants)].map(escapeRegExp).join("|");
     const needle = new RegExp(`\\b(?:${alternatives})\\b`, "g");
     forEachParagraph(tree, (ctx) => {
       // Skip the definition itself. For an express definition that is the
@@ -1272,3 +1272,25 @@ function regularPlural(term: string): string | null {
   else plural = last + "s";
   return head + plural;
 }
+
+/**
+ * Regular English singular of a plural term's final word — the mirror of
+ * {@link regularPlural}, for a term defined in the plural ("Deliverables",
+ * "Affiliates", "Parties") that the body uses in the singular. Guarded by a
+ * round trip: the candidate singular is only accepted when re-pluralizing it
+ * reproduces the exact term, so a non-plural word ending in "s" ("Business" →
+ * "Busines" → "Businesses" ≠ "Business") is rejected. Returns null when no
+ * simple rule applies.
+ */
+function regularSingular(term: string): string | null {
+  const m = /^(.*?)(\S+)$/.exec(term);
+  if (!m) return null;
+  const [, head, last] = m as unknown as [string, string, string];
+  let singularLast: string | null = null;
+  if (/[^aeiou]ies$/i.test(last)) singularLast = last.replace(/ies$/i, "y");
+  else if (/(ses|xes|zes|ches|shes)$/i.test(last)) singularLast = last.replace(/es$/i, "");
+  else if (/[^s]s$/i.test(last)) singularLast = last.replace(/s$/i, "");
+  if (!singularLast) return null;
+  const candidate = head + singularLast;
+  return regularPlural(candidate) === term ? candidate : null;
+}