feat(p): link only OEM codes with a cross-reference match

Every OEM code was a link → unmatched codes (the majority — fasteners,
clips, body parts TecDoc doesn't carry) opened an empty "no
equivalents" page. Now the schema page batch-checks its codes against
the snapshot (POST /p/matched, one indexed query) and links ONLY the
matched ones; unmatched codes render as plain text. Copy stays for all.
No more dead-end empty pages from the parts panel.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/web/src/components/schema/parts-panel.tsx

@@ -37,6 +37,34 @@ export function PartsPanel({
   const viewedKeyRef = useRef<string | null>(null);
   const [copiedId, setCopiedId] = useState<string | null>(null);
   const [resolvingCode, setResolvingCode] = useState<string | null>(null);
+  // OEM codes that resolve to a non-empty cross-reference page. Only these are
+  // rendered as links — unmatched codes stay plain text so a click never lands
+  // on an empty "no equivalents" page. One batch lookup per parts list.
+  const [matchedOemCodes, setMatchedOemCodes] = useState<Set<string>>(new Set());
+
+  const oemCodes = useMemo(
+    () => [...new Set(parts.map((p) => p.oemCode).filter((c) => c && c !== "N/A"))],
+    [parts],
+  );
+
+  useEffect(() => {
+    if (oemCodes.length === 0) {
+      setMatchedOemCodes(new Set());
+      return;
+    }
+    let cancelled = false;
+    api
+      .post<{ matched: string[] }>("/p/matched", { codes: oemCodes })
+      .then((res) => {
+        if (!cancelled) setMatchedOemCodes(new Set(res?.matched ?? []));
+      })
+      .catch(() => {
+        if (!cancelled) setMatchedOemCodes(new Set());
+      });
+    return () => {
+      cancelled = true;
+    };
+  }, [oemCodes]);
 
   // PL24 "bk. tablo:NNN-NNN" cross-reference jump. Resolved at load → open the
   // target illustration directly. Unresolved (target branch not seeded yet) →
@@ -365,11 +393,13 @@ export function PartsPanel({
                             )}
                           </button>
                         )}
-                        {part.oemCode && part.oemCode !== "N/A" ? (
-                          // Click → OEM detail page (P cross-reference) in a
-                          // new tab so the catalog/schema context stays put. Plain
-                          // anchor (not router Link) — a fresh load resolves the
-                          // route and keeps this cell router-context-free.
+                        {part.oemCode &&
+                        part.oemCode !== "N/A" &&
+                        matchedOemCodes.has(part.oemCode) ? (
+                          // Link ONLY codes with a real cross-reference (new tab,
+                          // keeps catalog/schema context). Plain anchor, not router
+                          // Link — fresh load resolves the route, no router context
+                          // needed here. Unmatched codes fall through to plain text.
                           <a
                             href={`/dashboard/oem/${encodeURIComponent(part.oemCode)}`}
                             target="_blank"