SFT-8161: honour USE_BIP39_GENERATE

### extmod/trezor-firmware/core/embed/extmod/modtrezorcrypto/modtrezorcrypto-bip39.h
@@ -60,6 +60,10 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_1(
     mod_trezorcrypto_bip39_word_completion_mask_obj,
     mod_trezorcrypto_bip39_word_completion_mask);
 
+// py.mk asks for this to be off with -DUSE_BIP39_GENERATE=0, and nothing here read
+// the flag. Passport generates seeds in new_seed_task rather than through this.
+// Default to on where the flag is not set, so upstream builds are unaffected.
+#if !defined(USE_BIP39_GENERATE) || USE_BIP39_GENERATE
 /// def generate(strength: int) -> str:
 ///     """
 ///     Generate a mnemonic of given strength (128, 160, 192, 224 and 256 bits).
@@ -79,6 +83,7 @@ STATIC mp_obj_t mod_trezorcrypto_bip39_generate(mp_obj_t strength) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(mod_trezorcrypto_bip39_generate_obj,
                                  mod_trezorcrypto_bip39_generate);
+#endif
 
 /// def from_data(data: bytes) -> str:
 ///     """
@@ -177,8 +182,10 @@ STATIC const mp_rom_map_elem_t mod_trezorcrypto_bip39_globals_table[] = {
      MP_ROM_PTR(&mod_trezorcrypto_bip39_complete_word_obj)},
     {MP_ROM_QSTR(MP_QSTR_word_completion_mask),
      MP_ROM_PTR(&mod_trezorcrypto_bip39_word_completion_mask_obj)},
+#if !defined(USE_BIP39_GENERATE) || USE_BIP39_GENERATE
     {MP_ROM_QSTR(MP_QSTR_generate),
      MP_ROM_PTR(&mod_trezorcrypto_bip39_generate_obj)},
+#endif
     {MP_ROM_QSTR(MP_QSTR_from_data),
      MP_ROM_PTR(&mod_trezorcrypto_bip39_from_data_obj)},
     {MP_ROM_QSTR(MP_QSTR_check), MP_ROM_PTR(&mod_trezorcrypto_bip39_check_obj)},

### ports/stm32/boards/Passport/modules/tests/test_unit.py
@@ -28,6 +28,10 @@ def test_passphrase_length(test):
     assert test('passphrase_length.py') == b'OK'
 
 
+def test_crypto_api_surface(test):
+    assert test('crypto_api_surface.py') == b'OK'
+
+
 def test_psbt_multisig_approval(test):
     assert test('psbt_multisig_approval.py') == b'OK'
 

### ports/stm32/boards/Passport/modules/tests/unit/crypto_api_surface.py
@@ -0,0 +1,31 @@
+# SPDX-FileCopyrightText: © 2026 Foundation Devices, Inc. <hello@foundation.xyz>
+# SPDX-License-Identifier: GPL-3.0-or-later
+#
+# py.mk sets -DUSE_BIP39_GENERATE=0, so bip39.generate() is not part of the API
+# surface. Passport generates seeds in new_seed_task rather than through it.
+
+import trezorcrypto
+
+assert not hasattr(trezorcrypto.bip39, 'generate'), \
+    'bip39.generate() is exposed again, and USE_BIP39_GENERATE asks for it to be off'
+
+# Everything else the seed flows use is still there.
+for name in ('from_data', 'seed', 'check', 'find_word', 'complete_word',
+             'word_completion_mask', 'get_word'):
+    assert hasattr(trezorcrypto.bip39, name), 'bip39.{} went missing'.format(name)
+
+# from_data() takes bytes the caller chose, so it stays: new_seed_task hands it the
+# result of its own noise request. A known vector, to show it still works.
+assert trezorcrypto.bip39.from_data(bytes(16)) == \
+    'abandon abandon abandon abandon abandon abandon abandon abandon ' \
+    'abandon abandon abandon about'
+assert trezorcrypto.bip39.check(trezorcrypto.bip39.from_data(bytes(32)))
+
+# ext_settings.py relies on both of these for wear levelling and padding.
+assert len(trezorcrypto.random.bytes(256)) == 256
+
+options = list(range(16))
+trezorcrypto.random.shuffle(options)
+assert sorted(options) == list(range(16))
+
+return_value.write(b'OK')

### ports/stm32/boards/Passport/noise.c
@@ -166,6 +166,14 @@ bool noise_get_random_bytes(uint8_t sources, void* buf, size_t buf_len) {
 }
 
 // trezor-firmware randomness functions
+//
+// These back trezor-crypto's internal randomness, where an avalanche sample per
+// call would be paid on every operation. Their consumers are blinding and nonce
+// material in ecdsa.c and zkp_context.c, and trezorcrypto.random, which
+// ext_settings.py uses for wear levelling and deniability padding.
+//
+// Secret generation is not one of them - see new_seed_task, which asks
+// noise_get_random_bytes() for every source.
 
 void random_reseed(const uint32_t value) {
     (void)value;