hide the rescan control on a source that cannot rescan

the card keyed off `sync.rescan` being null, which is what esplora
reports — and equally what nbxplorer reports before its first scan. so
the guard could not tell "unsupported" from "not yet run" and resolved
it the wrong way: every esplora wallet got a button that 501s.

canRescan carries the distinction explicitly.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/servers/sidecar/wallet/backends/onchain.ts

@@ -313,6 +313,7 @@ export class OnchainBackend extends BaseBackend {
       syncedAt: this.current?.at ?? null,
       stale: this.current !== null && Date.now() - this.current.at >= SCAN_TTL_MS,
       lastError: this.lastError,
+      canRescan: this.chain.startRescan !== undefined,
       rescan: this.chain.rescanState?.() ?? null,
     };
   }

src/servers/sidecar/wallet/types.ts

@@ -321,6 +321,14 @@ export type SyncState = {
   stale: boolean;
   /** The last refresh failure, still reported while the previous good data is being served. */
   lastError: string | null;
+  /**
+   * Whether this chain source can search the chain from scratch at all. False for Esplora, which asks
+   * about every address on every refresh and so has nothing to catch up on.
+   *
+   * Distinct from `rescan === null`, which is ALSO what a source that simply hasn't run one yet reports
+   * — conflating the two put a button that 501s in front of every Esplora wallet.
+   */
+  canRescan: boolean;
   /** A deep rescan in flight, or the outcome of the last one. Null from a source that cannot rescan. */
   rescan: RescanState | null;
 };

src/workspaces/officerdev/src/apps/Wallet/RescanCard.tsx

@@ -23,10 +23,10 @@ export const RescanCard = ({ walletId }: RescanCardProps) => {
   const { sync } = useBalances(walletId);
   const { rescan } = useWalletOperations(walletId);
 
-  // `sync.rescan` is null from a source with no rescan endpoint AND from one that has simply never run
-  // one, so the card has to stay visible in the second case. `sync` itself being null is a node backend,
-  // which owns its own coins and has nothing to look for.
-  if (!sync) return null;
+  // `sync` null is a node backend, which owns its own coins and has nothing to look for. `canRescan`
+  // false is Esplora. Note this cannot key off `sync.rescan` being null — that is equally what NBXplorer
+  // reports before its first scan, which is exactly when the card is most needed.
+  if (!sync?.canRescan) return null;
 
   const state = sync.rescan;
   const running = state?.running === true;

src/workspaces/officerdev/src/apps/Wallet/shared.ts

@@ -123,6 +123,12 @@ export type SyncState = {
   syncedAt: number | null;
   stale: boolean;
   lastError: string | null;
+  /**
+   * Whether the chain source can search the chain from scratch at all — false for Esplora, which reads
+   * every address on every refresh and has nothing to catch up on. Gate the control on this, NOT on
+   * `rescan === null`: that is also what a source reports before its first scan.
+   */
+  canRescan: boolean;
   /** A deep rescan in flight, or the last one's outcome. Null from a chain source that cannot rescan. */
   rescan: RescanState | null;
 };