intake: a duplicate card that refuses a purchase must say what to do instead

The header (merchant, date, total) is a purchase's identity here, so a genuine
second identical purchase — two of the same coffee, one shop, one day — reads
as a re-share and is refused. That default is right; a re-share is far commoner
than a repeat. But the card said only "Nothing was changed", which is a dead
end: the money is real and the ledger silently never gets it. Say to add it in
the app.

src/lib/intake-blocks.ts

@@ -155,7 +155,12 @@ export function askCard(c: CardInput): { blocks: Block[]; text: string } {
 
 export function duplicateCard(c: { merchant: string | null; total: number | null; transactionId: number | null; captureId: number | null; batchId: string | null; currency?: string | null }): { blocks: Block[]; text: string } {
   const where = c.transactionId ? `transaction ${c.transactionId}` : c.captureId ? `pantry capture ${c.captureId}` : c.batchId ? `batch ${esc(c.batchId)}` : "an earlier upload";
-  const text = `Already handled — ${esc(c.merchant) || "this order"} ${c.total !== null ? money(c.total, c.currency) : ""} is ${where}. Nothing was changed.`.replace(/\s+/g, " ");
+  // The header (merchant, date, total) IS the identity of a purchase here, so a
+  // genuine SECOND identical purchase — two of the same coffee, one day, one shop
+  // — reads as a re-share and is refused. That is the right default (a re-share is
+  // far commoner than a repeat) but it is a dead end without this sentence: the
+  // card must say what to do instead, or the ledger quietly loses the second one.
+  const text = `Already handled — ${esc(c.merchant) || "this order"} ${c.total !== null ? money(c.total, c.currency) : ""} is ${where}. Nothing was changed — if this really is a second, separate purchase, add it in the app.`.replace(/\s+/g, " ");
   return { text, blocks: [section(`:repeat: ${text}`)] };
 }