Trade mix: name positions by a contract index that never expires

A Tradovate position opened before this build (so its entry wasn't recorded)
was named from the contract cache, whose entries expire after 30 minutes:
Majd's CL longs showed as #3273057. The resolver now also keeps a lasting
contract id → root index, which the mix reads after its recorded entries.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/contract-resolver.ts

@@ -37,8 +37,13 @@ const PROBE_WINDOW = 6;
 // route handlers (settings page, manual trades) never see.
 const _g = globalThis as typeof globalThis & {
     __contractCache?: Map<string, { contract: ResolvedContract; resolvedAt: number }>;
+    __contractRoots?: Map<string, string>;
 };
 const cache = (_g.__contractCache ??= new Map());
+/** Contract id → the root it was resolved for. Unlike the cache it never
+ *  expires: a position opened hours ago still needs its instrument's name
+ *  (lib/trade-mix.ts). Front months are few, so it stays small. */
+const roots = (_g.__contractRoots ??= new Map());
 const CACHE_TTL_MS = 30 * 60 * 1000; // 30 minutes
 
 export function getCachedContract(symbol: string): ResolvedContract | null {
@@ -51,6 +56,12 @@ export function getCachedContract(symbol: string): ResolvedContract | null {
     return entry.contract;
 }
 
+/** The root a resolved contract id belongs to, however long ago it was
+ *  resolved; null for one this process never resolved. */
+export function rootOfContract(contractId: number | string): string | null {
+    return roots.get(String(contractId)) ?? null;
+}
+
 export function getAllCachedContracts(): Record<string, ResolvedContract | null> {
     const result: Record<string, ResolvedContract | null> = {};
     for (const [symbol, entry] of cache) {
@@ -205,6 +216,7 @@ export async function resolveContracts(
             };
             results[sym] = contract;
             cache.set(sym, { contract, resolvedAt: Date.now() });
+            roots.set(String(contract.id), sym);
 
             if (rolledFrom) {
                 console.log(`[contract-resolver] ${sym}: ${rolledFrom} → ${match.name} ROLLED (by volume)`);