Correct stale Prime review and about copy

The review and about screens still described a Sepolia-only wallet and
displayed a wei-exact fee.

- "How it works" and the onboarding banner claimed Sepolia-only assets, and
  the approval screen told the user to await Sepolia confirmation, which is
  wrong after a Bitcoin transfer. The approval wording is now chain-neutral.
- The review screen showed USDT where the companion shows USD~T.
- Maximum fees rendered as eighteen decimals. They are now shortened to eight,
  always rounding up: this figure is the ceiling the user authorises, so it
  must never read lower than what the transaction can spend, and dust must
  never display as zero. Six decimals collapsed a typical Sepolia gas cost to
  one significant digit, so eight is the floor for a useful review.

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

Author: BitcoinQnA

prime-app/i18n/en.json

@@ -6,11 +6,11 @@
   "about.approvalTitle": "Approve every transfer",
   "about.content": "Tether Wallet uses the phone for the wallet experience and Passport Prime for custody and approval.",
   "about.eyebrow": "HOW IT WORKS",
-  "about.phoneContent": "The phone builds and broadcasts Sepolia transactions.",
+  "about.phoneContent": "The phone builds and broadcasts Sepolia and Bitcoin Testnet transactions.",
   "about.phoneTitle": "Tether Wallet on your phone",
   "about.primeContent": "The private key is derived and used only inside Passport.",
   "about.primeTitle": "Keys stay on Passport Prime",
-  "about.testnet": "This proof of concept uses Sepolia testnet assets only.",
+  "about.testnet": "This proof of concept uses Sepolia and Bitcoin Testnet assets only.",
   "about.title": "One wallet, two secure roles",
   "brand.name": "Tether Wallet",
   "common.button.back": "Back",
@@ -63,7 +63,7 @@
   "onboarding.pairTitle": "Pair securely",
   "onboarding.reviewContent": "See exactly what the phone asks Passport to sign.",
   "onboarding.reviewTitle": "Review every transfer",
-  "onboarding.testnet": "Sepolia testnet only • Do not send real funds",
+  "onboarding.testnet": "Testnet only • Do not send real funds",
   "onboarding.title": "Your Tether wallet. Secured by Passport.",
   "pairing.content": "In Tether Wallet, choose Passport Prime and scan this code.",
   "pairing.contentConnected": "Scan this second code in Tether Wallet to exchange secure identities.",
@@ -87,7 +87,7 @@
   "result.action": "Back to wallet",
   "result.content": "Passport Prime signed the transfer and securely returned it to your companion app.",
   "result.eyebrow": "TRANSFER APPROVED",
-  "result.next": "Next, check your companion app for Sepolia network confirmation.",
+  "result.next": "Next, check your companion app for network confirmation.",
   "result.title": "Transfer approved",
   "review.amount": "Amount",
   "review.maximumFee": "Maximum network fee",

prime-app/src/evm.rs

@@ -191,7 +191,7 @@ impl EvmWallet {
 
         Ok(PreparedTransaction {
             request,
-            review: Review { asset, amount, recipient, maximum_fee: format_units(total_fee, 18) },
+            review: Review { asset, amount, recipient, maximum_fee: format_fee_ceil(total_fee) },
         })
     }
 
@@ -405,6 +405,18 @@ fn length_prefix(length: usize, short_base: u8, long_base: u8) -> Vec<u8> {
     prefix
 }
 
+/// Wei-exact fees render as eighteen decimals, which is unreadable on the
+/// review screen. Shorten to eight, always rounding *up*: this is the maximum
+/// the user is authorising, so the figure on screen must never be lower than
+/// what the transaction can actually spend, and a non-zero fee must never
+/// display as zero. Eight decimals keeps several significant digits on typical
+/// Sepolia gas costs, where six would collapse them to a single one.
+fn format_fee_ceil(value_wei: u128) -> String {
+    const SCALE: u128 = 10_000_000_000; // 18 decimals down to 8
+    let ceiled = value_wei.div_ceil(SCALE);
+    format_units(ceiled, 8)
+}
+
 fn format_units(value: u128, decimals: usize) -> String {
     let mut digits = value.to_string();
     if decimals == 0 {
@@ -430,6 +442,22 @@ mod tests {
 
     const SEED: [u8; 32] = [0x42; 32];
 
+    #[test]
+    fn displayed_maximum_fee_never_understates_the_authorised_amount() {
+        // The real fee from a Sepolia USD~T transfer, which rendered as
+        // 0.000099281419373928 before this shortened it.
+        assert_eq!(format_fee_ceil(99_281_419_373_928), "0.00009929");
+
+        // Rounding is upward, so the figure on screen is never lower than what
+        // the transaction can spend, and dust never displays as zero.
+        assert_eq!(format_fee_ceil(1), "0.00000001");
+        assert_eq!(format_fee_ceil(10_000_000_001), "0.00000002");
+
+        // Exact multiples stay exact, and a genuinely zero fee stays zero.
+        assert_eq!(format_fee_ceil(20_000_000_000), "0.00000002");
+        assert_eq!(format_fee_ceil(0), "0.0");
+    }
+
     fn base_request() -> WdkEvmSignTransactionRequest {
         let wallet = EvmWallet::new(SEED);
         WdkEvmSignTransactionRequest {

prime-app/src/main.rs

@@ -356,7 +356,7 @@ fn handle_signing_requests(ui: &AppWindow, state: &StoredValue<AppState>) {
                         let view = ui.global::<State>();
                         view.set_asset(match prepared.review.asset {
                             Asset::Eth => SharedString::from("ETH"),
-                            Asset::Usdt => SharedString::from("USDT"),
+                            Asset::Usdt => SharedString::from("USD₮"),
                         });
                         view.set_amount(prepared.review.amount.clone().into());
                         view.set_recipient(prepared.review.recipient.clone().into());