fix(frontend): cap schema-linking graph on promoted count + signals in table Perché

- Cap counts promoted candidates only (was all candidates); reuse promoted list (DRY)
- New test: 10 promoted + 50 excluded must not cap, graph stays available
- Extract reasonFor() helper; table Perché falls back to signal keys like the flowchart

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

frontend/src/viewers/SchemaLinkingViewer.test.tsx

@@ -55,3 +55,30 @@ test("(c) oversized linking (>45) shows cap notice", () => {
     screen.getByText(/troppi elementi per il grafico/i)
   ).toBeInTheDocument();
 });
+
+test("(d) ~10 promoted + ~50 excluded does NOT cap; graph is available", async () => {
+  const mixedLinking = {
+    question: "caso misto",
+    candidates: [
+      ...Array.from({ length: 10 }, (_, i) => ({
+        kind: "table" as const,
+        name: `kept_${i}`,
+        decision: "promoted" as const,
+      })),
+      ...Array.from({ length: 50 }, (_, i) => ({
+        kind: "table" as const,
+        name: `dropped_${i}`,
+        decision: "excluded" as const,
+      })),
+    ],
+    joins: [],
+    excluded: [],
+    open_questions: [],
+  };
+  render(<SchemaLinkingViewer linking={mixedLinking} />);
+  expect(
+    screen.queryByText(/troppi elementi per il grafico/i)
+  ).not.toBeInTheDocument();
+  // Grafico (mermaid) view is the default and renders the mocked svg.
+  await waitFor(() => expect(screen.getByTestId("mm")).toBeInTheDocument());
+});

frontend/src/viewers/SchemaLinkingViewer.tsx

@@ -25,19 +25,23 @@ export interface SchemaLinking {
   open_questions: string[];
 }
 
-function buildFlowchart(candidates: Candidate[], joins: Join[]): string {
+/** The inline "perché" comment for a candidate: evidence first, then signal keys. */
-  const promoted = candidates.filter((c) => c.decision === "promoted");
+function reasonFor(c: Candidate): string {
+  if (c.evidence?.length) return c.evidence[0];
+  if (c.signals && Object.keys(c.signals).length)
+    return Object.keys(c.signals).join(", ");
+  return "";
+}
+
+function buildFlowchart(promoted: Candidate[], joins: Join[]): string {
   const nodeId = (name: string) => name.replace(/[^a-zA-Z0-9]/g, "_");
 
   const lines: string[] = ["flowchart TB"];
 
   for (const c of promoted) {
     const id = nodeId(c.name);
-    const tooltip = c.evidence?.length
+    const reason = reasonFor(c);
-      ? ` %% ${c.evidence[0]}`
+    const tooltip = reason ? ` %% ${reason}` : "";
-      : c.signals && Object.keys(c.signals).length
-      ? ` %% ${Object.keys(c.signals).join(", ")}`
-      : "";
     const shape = c.kind === "table" ? `[${c.name}]` : `(${c.name})`;
     lines.push(`  ${id}${shape}${tooltip}`);
   }
@@ -52,8 +56,7 @@ function buildFlowchart(candidates: Candidate[], joins: Join[]): string {
   return lines.join("\n");
 }
 
-function buildHierarchicalRows(candidates: Candidate[]) {
+function buildHierarchicalRows(promoted: Candidate[]) {
-  const promoted = candidates.filter((c) => c.decision === "promoted");
   const tables = promoted.filter((c) => c.kind === "table");
   const columns = promoted.filter((c) => c.kind === "column");
 
@@ -75,7 +78,9 @@ function buildHierarchicalRows(candidates: Candidate[]) {
 }
 
 export function SchemaLinkingViewer({ linking }: { linking: SchemaLinking }) {
-  const oversized = linking.candidates.length > CAP;
+  const promoted = linking.candidates.filter((c) => c.decision === "promoted");
+  // The graph only contains promoted candidates, so cap on that count.
+  const oversized = promoted.length > CAP;
   const [view, setView] = useState<"chart" | "table">(
     oversized ? "table" : "chart"
   );
@@ -84,16 +89,17 @@ export function SchemaLinkingViewer({ linking }: { linking: SchemaLinking }) {
   useEffect(() => {
     if (view !== "chart" || oversized) return;
     let cancelled = false;
-    const def = buildFlowchart(linking.candidates, linking.joins);
+    const def = buildFlowchart(promoted, linking.joins);
     renderMermaid(def).then((s) => {
       if (!cancelled) setSvg(s);
     });
     return () => {
       cancelled = true;
     };
+    // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [view, linking, oversized]);
 
-  const { grouped, orphans } = buildHierarchicalRows(linking.candidates);
+  const { grouped, orphans } = buildHierarchicalRows(promoted);
 
   return (
     <div className="schema-linking-viewer">
@@ -143,7 +149,7 @@ export function SchemaLinkingViewer({ linking }: { linking: SchemaLinking }) {
                   <td className="py-1 pl-1">{table.name}</td>
                   <td>tabella</td>
                   <td className="text-xs text-muted-foreground">
-                    {table.evidence?.[0] ?? ""}
+                    {reasonFor(table)}
                   </td>
                 </tr>
                 {cols.map((col) => (
@@ -153,7 +159,7 @@ export function SchemaLinkingViewer({ linking }: { linking: SchemaLinking }) {
                     </td>
                     <td>colonna</td>
                     <td className="text-xs text-muted-foreground">
-                      {col.evidence?.[0] ?? ""}
+                      {reasonFor(col)}
                     </td>
                   </tr>
                 ))}
@@ -166,7 +172,7 @@ export function SchemaLinkingViewer({ linking }: { linking: SchemaLinking }) {
                 </td>
                 <td>colonna</td>
                 <td className="text-xs text-muted-foreground">
-                  {col.evidence?.[0] ?? ""}
+                  {reasonFor(col)}
                 </td>
               </tr>
             ))}