ui: display full transaction amounts

### CHANGELOG.md
@@ -8,6 +8,7 @@ customers cannot upgrade their bootloader, its changes are recorded separately.
 
 ### [Unreleased]
 - Add support for BitBoxSync
+- Display long transaction and swap amounts in full instead of truncating them
 
 ### v9.26.5
 - Fixed a crash when listing many backups over Bluetooth

### py/send_message.py
@@ -1094,10 +1094,10 @@ def address(display: bool = False) -> str:
             eprint("Aborted by user")
 
     def _sign_eth_tx(self) -> None:
-        # pylint: disable=line-too-long,too-many-branches
+        # pylint: disable=line-too-long,too-many-branches,too-many-statements
 
         inp = input(
-            "Select one of: 1=normal; 2=erc20; 3=erc721; 4=unknown erc20; 5=large data field; 6=BSC; 7=unknown network; 8=eip1559; 9=Arbitrum; 10=streaming (10KB data): "
+            "Select one of: 1=normal; 2=erc20; 3=erc721; 4=unknown erc20; 5=large data field; 6=BSC; 7=unknown network; 8=eip1559; 9=Arbitrum; 10=streaming (10KB data); 11=long amounts: "
         ).strip()
 
         chain_id = 1  # mainnet
@@ -1155,6 +1155,20 @@ def _sign_eth_tx(self) -> None:
             tx = rlp.encode([nonce, gas_price, gas_limit, recipient, value, data, v, r, s])
             if self._debug:
                 print(f"Streaming test transaction: {len(data)} bytes of data")
+        elif inp == "11":
+            # Exercise overflow handling for the send amount, total, and fee screens.
+            nonce = b"\x01"
+            gas_price = b"\xff" * 8
+            gas_limit = b"\xff" * 8
+            recipient = (
+                b"\x11\x22\x33\x44\x55\x66\x77\x88\x99\xaa\xbb\xcc\xdd\xee\xff\x00\x11\x22\x33\x44"
+            )
+            value = b"\xff" * 32
+            data = b""
+            v = b"\x25"  # chain_id=1
+            r = b"\x01" * 32
+            s = b"\x01" * 32
+            tx = rlp.encode([nonce, gas_price, gas_limit, recipient, value, data, v, r, s])
         else:
             print("None selected")
             return

### src/rust/bitbox02-rust/src/hww/api/ethereum/amount.rs
@@ -11,26 +11,16 @@ pub struct Amount<'a> {
 }
 
 impl Amount<'_> {
-    /// Formats the amount with the right number of decimal places, suffixed with the unit. If the
-    /// value (without the unit suffix) is too long to fit on the screen, it will be truncated and
-    /// ellipsis ('...')  are appended.
+    /// Formats the full amount with the right number of decimal places, suffixed with the unit.
     ///
     /// Example:
     /// - unit: ETH,
     /// - decimals: 18,
     /// - value: 38723987932742983742983742
-    /// - returns: "38723987.9327... ETH"
+    /// - returns: "38723987.932742983742983742 ETH"
     pub fn format(&self) -> String {
-        // Truncate the number at this many chars and append '...' if truncated.
-        // Empirically found to fit on one line on the screen (including unit).
-        // TODO: take into account long unit strings.
-        const TRUNCATE_SIZE: usize = 13;
         let v = util::decimal::format(&self.value, self.decimals);
-        if v.len() > TRUNCATE_SIZE {
-            format!("{}... {}", &v[..TRUNCATE_SIZE], self.unit)
-        } else {
-            format!("{} {}", v, self.unit)
-        }
+        format!("{} {}", v, self.unit)
     }
 }
 
@@ -83,7 +73,7 @@ mod tests {
                 bigendian: b"\x20\x08\x1f\x97\x9a\x5c\x8d\x47\x29\x0e\x3e",
                 decimals: 18,
                 unit: "ETH",
-                expected_result: "38723987.9327... ETH",
+                expected_result: "38723987.932742983742983742 ETH",
             },
             Test {
                 // 123456
@@ -111,7 +101,7 @@ mod tests {
                 bigendian: b"\x01\x22\x08\x3f\x97\xf2",
                 decimals: 11,
                 unit: "ETH",
-                expected_result: "12.4567890123... ETH",
+                expected_result: "12.45678901234 ETH",
             },
             Test {
                 // 123456

### src/rust/bitbox02-rust/src/hww/api/payment_request.rs
@@ -4,7 +4,6 @@ use super::Error;
 use crate::hal::ui::ConfirmParams;
 use crate::pb;
 
-use alloc::string::String;
 use alloc::vec::Vec;
 #[cfg(feature = "app-ethereum")]
 use num_bigint::BigUint;
@@ -23,8 +22,9 @@ use bitcoin::secp256k1;
 
 // Arbitrary limit on number of memos that a payment request can show to the user.
 const MAX_MEMOS_NUM: usize = 3;
-// Keep in sync with `hww/api/ethereum/amount.rs`.
-const COIN_PURCHASE_AMOUNT_TRUNCATE_SIZE: usize = 13;
+// Coin purchase amounts are externally supplied display strings. Keep them within the documented
+// UI text limit so every supported device can show them in full.
+const MAX_COIN_PURCHASE_AMOUNT_LEN: usize = 200;
 
 struct Identity {
     name: &'static str,
@@ -78,6 +78,9 @@ pub(super) fn contains_coin_purchase_memo(payment_request: &pb::BtcPaymentReques
 /// "<positive-number> <unit>", where the number may be an integer or decimal,
 /// and returns the amount/unit parts.
 fn parse_coin_purchase_amount(amount: &str) -> Result<(&str, &str), Error> {
+    if amount.len() > MAX_COIN_PURCHASE_AMOUNT_LEN {
+        return Err(Error::InvalidInput);
+    }
     let mut parts = amount.split_ascii_whitespace();
     let destination_amount = parts.next().ok_or(Error::InvalidInput)?;
     let destination_unit = parts.next().ok_or(Error::InvalidInput)?;
@@ -114,34 +117,11 @@ fn parse_coin_purchase_amount(amount: &str) -> Result<(&str, &str), Error> {
     if integer.bytes().chain(fractional.bytes()).all(|b| b == b'0') {
         return Err(Error::InvalidInput);
     }
-
-    Ok((destination_amount, destination_unit))
-}
-
-/// Formats a coin purchase amount for display on the swap screen.
-///
-/// This matches the truncation budget used by Ethereum amount formatting, but only truncates after
-/// the decimal point so integer digits are always preserved.
-fn format_coin_purchase_amount_for_display(amount: &str) -> Result<String, Error> {
-    let (destination_amount, destination_unit) = parse_coin_purchase_amount(amount)?;
-
-    if destination_amount.len() <= COIN_PURCHASE_AMOUNT_TRUNCATE_SIZE {
-        return Ok(amount.into());
-    }
-
-    let Some(decimal_position) = destination_amount.find('.') else {
-        return Ok(amount.into());
-    };
-
-    if decimal_position + 1 >= COIN_PURCHASE_AMOUNT_TRUNCATE_SIZE {
-        return Ok(amount.into());
+    if !destination_unit.bytes().all(|b| b.is_ascii_alphanumeric()) {
+        return Err(Error::InvalidInput);
     }
 
-    Ok(format!(
-        "{}... {}",
-        &destination_amount[..COIN_PURCHASE_AMOUNT_TRUNCATE_SIZE],
-        destination_unit,
-    ))
+    Ok((destination_amount, destination_unit))
 }
 
 /// Prompt the user to verify the payment request UI flow.
@@ -183,14 +163,9 @@ pub async fn user_verify(
             Memo {
                 memo: Some(memo::Memo::CoinPurchaseMemo(coin_purchase_memo)),
             } => {
-                let displayed_destination_amount =
-                    format_coin_purchase_amount_for_display(&coin_purchase_memo.amount)?;
+                parse_coin_purchase_amount(&coin_purchase_memo.amount)?;
                 hal.ui()
-                    .confirm_swap(
-                        "Swap",
-                        displayed_source_amount,
-                        &displayed_destination_amount,
-                    )
+                    .confirm_swap("Swap", displayed_source_amount, &coin_purchase_memo.amount)
                     .await?;
             }
             _ => return Err(Error::InvalidInput),
@@ -623,35 +598,17 @@ mod tests {
             "1\nETH",
             "\n\n\n\n\n1 ETH",
             "1\rETH",
+            "1 ETH!",
+            "1 Ξ",
         ] {
             assert_eq!(parse_coin_purchase_amount(amount), Err(Error::InvalidInput));
         }
-    }
 
-    #[test]
-    fn test_format_coin_purchase_amount_for_display() {
-        assert_eq!(
-            format_coin_purchase_amount_for_display("0.25 ETH"),
-            Ok("0.25 ETH".into())
-        );
-        assert_eq!(
-            format_coin_purchase_amount_for_display("12.45678901234 ETH"),
-            Ok("12.4567890123... ETH".into())
-        );
-        assert_eq!(
-            format_coin_purchase_amount_for_display("1.2345678901234 BTC"),
-            Ok("1.23456789012... BTC".into())
-        );
-        assert_eq!(
-            format_coin_purchase_amount_for_display("12345678901234 ETH"),
-            Ok("12345678901234 ETH".into())
-        );
-        assert_eq!(
-            format_coin_purchase_amount_for_display("123456789012.34 ETH"),
-            Ok("123456789012.34 ETH".into())
-        );
+        let max_amount = format!("{} ETH", "1".repeat(MAX_COIN_PURCHASE_AMOUNT_LEN - 4));
+        assert!(parse_coin_purchase_amount(&max_amount).is_ok());
+        let oversized_amount = format!("{} ETH", "1".repeat(MAX_COIN_PURCHASE_AMOUNT_LEN - 3));
         assert_eq!(
-            format_coin_purchase_amount_for_display("foo ETH"),
+            parse_coin_purchase_amount(&oversized_amount),
             Err(Error::InvalidInput)
         );
     }
@@ -1649,7 +1606,7 @@ mod tests {
 
     #[cfg(feature = "app-ethereum")]
     #[async_test::test]
-    async fn test_user_verify_swap_truncated_destination_amount() {
+    async fn test_user_verify_swap_long_destination_amount() {
         let mut mock_hal = TestingHal::new();
         user_verify(
             &mut mock_hal,
@@ -1680,7 +1637,7 @@ mod tests {
                 Screen::Swap {
                     title: "Swap".into(),
                     from: "0.25000000 BTC".into(),
-                    to: "12.4567890123... ETH".into(),
+                    to: "12.45678901234 ETH".into(),
                 },
             ]
         );

### src/rust/bitbox02-sys/build.rs
@@ -86,6 +86,7 @@ const ALLOWLIST_FNS: &[&str] = &[
     "keystore_bip39_mnemonic_to_seed",
     "keystore_get_bip39_word",
     "label_create",
+    "label_fits_width",
     "memory_add_noise_remote_static_pubkey",
     "memory_ble_enable",
     "memory_ble_enabled",

### src/rust/bitbox02/src/hal/ui.rs
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: Apache-2.0
 
+use alloc::format;
 use alloc::string::String;
 use core::marker::PhantomData;
 use core::time::Duration;
@@ -83,6 +84,25 @@ impl<Timer> BitBox02Ui<Timer> {
     }
 }
 
+impl<Timer: bitbox_hal::timer::Timer> BitBox02Ui<Timer> {
+    async fn review_value(
+        &mut self,
+        title: &str,
+        value: &str,
+        longtouch: bool,
+    ) -> Result<(), UserAbort> {
+        self.confirm(&ConfirmParams {
+            title,
+            body: value,
+            scrollable: true,
+            longtouch,
+            accept_is_nextarrow: !longtouch,
+            ..Default::default()
+        })
+        .await
+    }
+}
+
 impl<Timer> Default for BitBox02Ui<Timer> {
     fn default() -> Self {
         Self::new()
@@ -128,6 +148,12 @@ impl<Timer: bitbox_hal::timer::Timer> Ui for BitBox02Ui<Timer> {
 
     #[inline(always)]
     async fn confirm_swap(&mut self, title: &str, from: &str, to: &str) -> Result<(), UserAbort> {
+        if !crate::ui::transaction_amount_fits(from) || !crate::ui::transaction_amount_fits(to) {
+            let from_title = format!("{title} from");
+            self.review_value(&from_title, from, false).await?;
+            let to_title = format!("{title} to");
+            return self.review_value(&to_title, to, false).await;
+        }
         match crate::ui::confirm_swap(title, from, to).await {
             crate::ui::ConfirmResponse::Approved => Ok(()),
             crate::ui::ConfirmResponse::Cancelled => Err(UserAbort),
@@ -136,6 +162,10 @@ impl<Timer: bitbox_hal::timer::Timer> Ui for BitBox02Ui<Timer> {
 
     #[inline(always)]
     async fn verify_recipient(&mut self, recipient: &str, amount: &str) -> Result<(), UserAbort> {
+        if !crate::ui::transaction_amount_fits(amount) {
+            self.review_value("Amount", amount, false).await?;
+            return self.review_value("Recipient", recipient, false).await;
+        }
         match crate::ui::confirm_transaction_address(amount, recipient).await {
             crate::ui::ConfirmResponse::Approved => Ok(()),
             crate::ui::ConfirmResponse::Cancelled => Err(UserAbort),
@@ -149,6 +179,10 @@ impl<Timer: bitbox_hal::timer::Timer> Ui for BitBox02Ui<Timer> {
         fee: &str,
         longtouch: bool,
     ) -> Result<(), UserAbort> {
+        if !crate::ui::transaction_amount_fits(total) || !crate::ui::transaction_fee_fits(fee) {
+            self.review_value("Total", total, false).await?;
+            return self.review_value("Fee", fee, longtouch).await;
+        }
         match crate::ui::confirm_transaction_fee(total, fee, longtouch).await {
             crate::ui::ConfirmResponse::Approved => Ok(()),
             crate::ui::ConfirmResponse::Cancelled => Err(UserAbort),

### src/rust/bitbox02/src/ui/ui.rs
@@ -15,6 +15,25 @@ use alloc::vec::Vec;
 use core::cell::RefCell;
 use core::task::{Poll, Waker};
 
+fn label_fits_width(text: &str, font: *const bitbox02_sys::UG_FONT) -> bool {
+    let text = util::strings::str_to_cstr_vec(text).unwrap();
+    unsafe { bitbox02_sys::label_fits_width(text.as_ptr(), font, bitbox02_sys::SCREEN_WIDTH as _) }
+}
+
+/// Returns true if the amount fits the transaction screen, using the smaller font if necessary.
+pub fn transaction_amount_fits(amount: &str) -> bool {
+    if label_fits_width(amount, unsafe { &bitbox02_sys::font_font_a_11X10 }) {
+        true
+    } else {
+        label_fits_width(amount, unsafe { &bitbox02_sys::font_font_a_9X9 })
+    }
+}
+
+/// Returns true if the fee fits the transaction screen's smaller fee font.
+pub fn transaction_fee_fits(fee: &str) -> bool {
+    label_fits_width(fee, unsafe { &bitbox02_sys::font_font_a_9X9 })
+}
+
 /// Wraps the C component_t to be used in Rust.
 pub struct Component {
     component: *mut bitbox02_sys::component_t,

### src/rust/bitbox02/src/ui/ui_stub.rs
@@ -87,6 +87,14 @@ pub async fn confirm_transaction_fee(
     panic!("not used");
 }
 
+pub fn transaction_amount_fits(_amount: &str) -> bool {
+    true
+}
+
+pub fn transaction_fee_fits(_fee: &str) -> bool {
+    true
+}
+
 pub fn screen_stack_pop_all() {}
 
 pub fn progress_create(_title: &str) -> Component {

### src/rust/bitbox02/src/ui/ui_stub_c_unit_tests.rs
@@ -110,6 +110,14 @@ pub async fn confirm_transaction_fee(
     ConfirmResponse::Approved
 }
 
+pub fn transaction_amount_fits(_amount: &str) -> bool {
+    true
+}
+
+pub fn transaction_fee_fits(_fee: &str) -> bool {
+    true
+}
+
 pub fn screen_stack_pop_all() {}
 
 pub fn progress_create(_title: &str) -> Component {

### src/ui/components/confirm_swap.c
@@ -11,10 +11,6 @@
 #include <ui/fonts/arial_fonts.h>
 #include <util.h>
 
-// Empirically measured when the amount goes out of screen with the 11x10 font and we should switch
-// to the smaller 9x9 font.
-#define BIG_FONT_MAX_CHARS 19
-
 typedef struct {
     void (*callback)(bool accepted, void* user_data);
     void* user_data;
@@ -100,14 +96,8 @@ component_t* confirm_swap_create(
     component_t* title_component = label_create(title, &font_font_a_11X10, CENTER_TOP, confirm);
     ui_util_add_sub_component(confirm, title_component);
 
-    const UG_FONT* from_font = NULL;
-    if (strlen(from) > BIG_FONT_MAX_CHARS) {
-        from_font = &font_font_a_9X9;
-    }
-    const UG_FONT* to_font = NULL;
-    if (strlen(to) > BIG_FONT_MAX_CHARS) {
-        to_font = &font_font_a_9X9;
-    }
+    const UG_FONT* from_font = label_fits_width(from, NULL, SCREEN_WIDTH) ? NULL : &font_font_a_9X9;
+    const UG_FONT* to_font = label_fits_width(to, NULL, SCREEN_WIDTH) ? NULL : &font_font_a_9X9;
 
     ui_util_add_sub_component(
         confirm, label_create_offset(from, from_font, CENTER_TOP, 0, 17, confirm));

### src/ui/components/confirm_transaction.c
@@ -13,10 +13,6 @@
 #include <ui/fonts/arial_fonts.h>
 #include <util.h>
 
-// Empirically measured when the amount goes out of screen with the 11x10 font and we should switch
-// to the smaller 9x9 font.
-#define BIG_FONT_MAX_CHARS 19
-
 typedef struct {
     bool has_address;
     // accepted: true means the user accepted the info shown, false means the user rejected the
@@ -126,10 +122,8 @@ static component_t* _confirm_transaction_create(
         ui_util_add_sub_component(
             confirm, label_create_offset(fee, &font_font_a_9X9, CENTER_TOP, 0, 50, confirm));
     }
-    const UG_FONT* amount_font = NULL;
-    if (strlen(amount) > BIG_FONT_MAX_CHARS) {
-        amount_font = &font_font_a_9X9;
-    }
+    const UG_FONT* amount_font =
+        label_fits_width(amount, NULL, SCREEN_WIDTH) ? NULL : &font_font_a_9X9;
     if (verify_total) {
         ui_util_add_sub_component(
             confirm, label_create_offset("Total", NULL, CENTER_TOP, 0, 8, confirm));

### src/ui/components/label.c
@@ -30,6 +30,15 @@ typedef struct {
 
 static void _measure_label_dimensions(component_t* label);
 
+bool label_fits_width(const char* text, const UG_FONT* font, uint16_t max_width)
+{
+    UG_S16 width;
+    UG_S16 height;
+    UG_FontSelect(font != NULL ? font : &font_font_a_11X10);
+    UG_MeasureStringNoBreak(&width, &height, text);
+    return width <= max_width;
+}
+
 void label_update(component_t* component, const char* text)
 {
     data_t* data = (data_t*)component->data;

### src/ui/components/label.h
@@ -12,6 +12,14 @@
 // Keep this in sync with src/rust/bitbox02-rust/src/workflow/confirm.rs:MAX_CONFIRM_BODY_SIZE.
 #define MAX_LABEL_SIZE 640
 
+/**
+ * Returns true if the text fits within max_width without wrapping using the given font.
+ * @param[in] text The text to measure.
+ * @param[in] font The font to use. If NULL, the default 11x10 font is used.
+ * @param[in] max_width The available width in pixels.
+ */
+bool label_fits_width(const char* text, const UG_FONT* font, uint16_t max_width);
+
 /**
  * Creates a label with the given font and positions it in the center.
  * @param[in] component The component to update.

### test/unit-test/test_ui_components.c
@@ -58,6 +58,11 @@ static void assert_ui_component_functions(component_t* component)
 
 static void test_ui_components_label(void** state)
 {
+    assert_true(label_fits_width("Test", &font_font_a_11X10, 128));
+    assert_true(label_fits_width("11111111111111111 BNB", &font_font_a_9X9, 128));
+    assert_false(
+        label_fits_width("This label is much wider than the screen", &font_font_a_9X9, 128));
+
     component_t* mock_component = fake_component_create();
 
     component_t* label = label_create("Test", NULL, CENTER, mock_component);