fix: narrow bare except blocks to stop hiding real errors (#877)

diff --git a/src/krux/key.py b/src/krux/key.py
index 7559f4e..8172e70 100644
--- a/src/krux/key.py
+++ b/src/krux/key.py
@@ -202,7 +202,7 @@ class Key:
                 Key.extract_root(mnemonic, passphrase, network).child(0).fingerprint,
                 pretty,
             )
-        except:
+        except Exception:
             pass
         return ""
 
diff --git a/src/krux/pages/__init__.py b/src/krux/pages/__init__.py
index ce97306..e04ef74 100644
--- a/src/krux/pages/__init__.py
+++ b/src/krux/pages/__init__.py
@@ -294,7 +294,7 @@ class Page:
         while not done:
             try:
                 code, num_parts = next(code_generator)
-            except:
+            except StopIteration:
                 code_generator = to_qr_codes(data, qr_data_width, qr_format)
                 code, num_parts = next(code_generator)
 
@@ -523,7 +523,7 @@ class Page:
             # Check for SD hot-plug
             with SDHandler():
                 return True
-        except:
+        except Exception:
             return False
 
     def shutdown(self):
diff --git a/src/krux/qr.py b/src/krux/qr.py
index 6345b37..29d7b04 100644
--- a/src/krux/qr.py
+++ b/src/krux/qr.py
@@ -308,7 +308,7 @@ def max_qr_bytes(max_width, encoding="byte"):
 
     try:
         return capacity_list[qr_version - 1]
-    except:
+    except IndexError:
         # Limited to version 20
         return capacity_list[-1]
 
@@ -406,6 +406,6 @@ def detect_format(data):
                     bbqr_encoding = data[2]
                     return FORMAT_BBQR, BBQrCode(None, bbqr_encoding, bbqr_file_type)
 
-    except:
+    except Exception:
         pass
     return qr_format, None
diff --git a/tests/pages/test_page.py b/tests/pages/test_page.py
index 3c4319a..b731697 100644
--- a/tests/pages/test_page.py
+++ b/tests/pages/test_page.py
@@ -137,6 +137,31 @@ def test_display_qr_code(mocker, m5stickv, mock_page_cls):
     assert ctx.input.wait_for_button.call_count == len(BTN_SEQUENCE)
 
 
+def test_display_qr_code_propagates_real_errors(mocker, m5stickv, mock_page_cls):
+    """A non-StopIteration error from the QR generator must propagate and must
+    NOT trigger a silent generator restart.
+
+    Regression for narrowing the bare ``except`` to ``except StopIteration``.
+    With the old bare except, a real error was swallowed and ``to_qr_codes``
+    was called a second time; now it surfaces immediately.
+    """
+    from krux.qr import FORMAT_NONE
+
+    def boom(*args, **kwargs):
+        raise ValueError("bad qr data")
+        yield  # pragma: no cover - makes boom a generator function
+
+    mocked = mocker.patch("krux.pages.to_qr_codes", side_effect=boom)
+    ctx = create_ctx(mocker, [])
+    page = mock_page_cls(ctx)
+
+    with pytest.raises(ValueError):
+        page.display_qr_codes(TEST_QR_DATA, FORMAT_NONE)
+
+    # The error surfaced on the first generator; no silent restart attempt.
+    assert mocked.call_count == 1
+
+
 def test_display_qr_code_light_theme(mocker, m5stickv, mock_page_cls):
     from krux.input import BUTTON_ENTER
     from krux.qr import FORMAT_NONE
@@ -646,3 +671,24 @@ def test_fit_to_line_not_crop_middle(mocker, multiple_devices, mock_page_cls):
         formatted_text = page.fit_to_line(case[TXT], case[PREFIX], crop_middle=False)
         assert len(formatted_text) <= max_chars_in_line
         assert formatted_text == case[device_type]
+
+
+def test_has_sd_card_handles_errors_and_propagates_signals(
+    mocker, m5stickv, mock_page_cls
+):
+    """has_sd_card returns False on genuine SD errors, but must NOT swallow
+    BaseException-level signals like KeyboardInterrupt.
+
+    Regression for narrowing the bare except to `except Exception`.
+    """
+    ctx = create_ctx(mocker, [])
+    page = mock_page_cls(ctx)
+
+    # Genuine SD failure (OSError) -> reported as "no SD card".
+    mocker.patch("krux.pages.SDHandler", side_effect=OSError("no card"))
+    assert page.has_sd_card() is False
+
+    # Shutdown signal during the check -> propagates, not swallowed into False.
+    mocker.patch("krux.pages.SDHandler", side_effect=KeyboardInterrupt)
+    with pytest.raises(KeyboardInterrupt):
+        page.has_sd_card()
diff --git a/tests/test_key.py b/tests/test_key.py
index cfc06b7..d4be6f3 100644
--- a/tests/test_key.py
+++ b/tests/test_key.py
@@ -728,3 +728,18 @@ def test_classmethod_extract_fingerprint(mocker, m5stickv, tdata):
     fingerprint = Key.extract_fingerprint("this is not a mnemonic", pretty=False)
 
     assert fingerprint == ""
+
+
+def test_extract_fingerprint_propagates_base_exceptions(mocker, m5stickv):
+    """extract_fingerprint catches genuine errors (returns "") but must NOT
+    swallow BaseException-level signals like KeyboardInterrupt.
+
+    Regression for narrowing the bare except to ``except Exception``.
+    """
+    import pytest
+    from krux.key import Key
+
+    mocker.patch.object(Key, "extract_root", side_effect=KeyboardInterrupt)
+
+    with pytest.raises(KeyboardInterrupt):
+        Key.extract_fingerprint("any mnemonic", pretty=False)
diff --git a/tests/test_qr.py b/tests/test_qr.py
index ccf524c..7572316 100644
--- a/tests/test_qr.py
+++ b/tests/test_qr.py
@@ -244,3 +244,35 @@ def test_parse_pmofn_rejects_invalid_index(m5stickv):
 
     with pytest.raises(ValueError, match="Invalid pMofN part index"):
         parse_pmofn_qr_part("p4of3 data")
+
+
+def test_detect_format_propagates_base_exceptions(mocker, m5stickv):
+    """detect_format catches genuine parsing errors (returns FORMAT_NONE) but
+    must NOT swallow BaseException-level signals like KeyboardInterrupt.
+
+    Regression for narrowing the bare except to ``except Exception``.
+    """
+    from krux.qr import detect_format
+
+    class Boom:
+        def startswith(self, _):
+            raise KeyboardInterrupt
+
+    with pytest.raises(KeyboardInterrupt):
+        detect_format(Boom())
+
+
+def test_max_qr_bytes_caps_at_last_version(mocker, m5stickv):
+    """A width beyond the supported version range falls back to the largest
+    capacity (exercises the narrowed `except IndexError`)."""
+    from krux.qr import max_qr_bytes, QR_CAPACITY_BYTE
+
+    assert max_qr_bytes(200) == QR_CAPACITY_BYTE[-1]
+
+
+def test_detect_format_returns_none_on_undecodable_data(mocker, m5stickv):
+    """Genuine parse errors (e.g. undecodable bytes) are caught and reported as
+    FORMAT_NONE (exercises the narrowed `except Exception`)."""
+    from krux.qr import detect_format, FORMAT_NONE
+
+    assert detect_format(b"\xff\xfe\xfd") == (FORMAT_NONE, None)