fix(settings): quick-switch write races, override parsing, stale custom fonts

Four fixes across the settings/prefs layer:

- Quick-switch toggles and reorders were read-modify-write against the
  async-echoed UI snapshot, so two rapid interactions reverted each
  other. Writes now go through SettingsPrefs.updateQuickSwitch, an
  atomic transform over the currently-stored value, via intent-level
  ViewModel ops; the MIN_ENABLED floor is re-checked inside the
  transform since the screen's guard reads the stale snapshot.

- parseReminderOverrides treated any unparseable stored value as an
  explicit empty override (no reminder). Only the deliberate 'none'
  sentinel means that now; garbage drops the entry so the calendar
  inherits the global default. Partially-valid values salvage their
  valid minutes.

- Replacing an already-active custom font never refreshed typography:
  the unchanged 'custom' token made AppFontSettings value-equal, so the
  StateFlow never re-emitted. A per-role import stamp now breaks
  equality on re-import (missing key = 0, backward compatible).

- The FontPicker custom preview resolved the font file unmemoized on
  every recomposition (disk stat + fresh FontFamily defeating the
  typeface cache); it's now remembered, keyed on the import stamp.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

app/src/test/java/de/jeanlucmakiola/calendula/data/prefs/SettingsPrefsTest.kt

@@ -5,6 +5,7 @@ import androidx.datastore.preferences.core.PreferenceDataStoreFactory
 import androidx.datastore.preferences.core.Preferences
 import com.google.common.truth.Truth.assertThat
 import de.jeanlucmakiola.calendula.domain.EventFormField
+import de.jeanlucmakiola.calendula.domain.FontRole
 import de.jeanlucmakiola.calendula.ui.agenda.AgendaRange
 import de.jeanlucmakiola.calendula.ui.common.CalendarView
 import de.jeanlucmakiola.calendula.ui.common.IMPLEMENTED_VIEWS
@@ -198,6 +199,22 @@ class SettingsPrefsTest {
         )
     }
 
+    @Test
+    fun `updateQuickSwitch transforms the stored value, so intents compose`(@TempDir tempDir: Path) = runTest {
+        val prefs = SettingsPrefs(newDataStore(tempDir))
+        // A toggle then a reorder, each expressed against the *stored* config —
+        // the reorder must not resurrect the just-disabled view (the stale-UI-
+        // snapshot race this API exists to prevent).
+        prefs.updateQuickSwitch { it.copy(enabled = it.enabled - CalendarView.Day) }
+        val newOrder = listOf(CalendarView.Agenda, CalendarView.Month, CalendarView.Week, CalendarView.Day)
+        prefs.updateQuickSwitch { it.copy(order = newOrder) }
+        val config = prefs.quickSwitchConfig.first()
+        assertThat(config.order).containsExactlyElementsIn(newOrder).inOrder()
+        assertThat(config.enabled).containsExactly(
+            CalendarView.Agenda, CalendarView.Month, CalendarView.Week,
+        )
+    }
+
     @Test
     fun `drawer order defaults to the implemented order and round-trips`(@TempDir tempDir: Path) = runTest {
         val prefs = SettingsPrefs(newDataStore(tempDir))
@@ -319,6 +336,26 @@ class SettingsPrefsTest {
         }
     }
 
+    @Test
+    fun `garbage per-calendar override values drop the entry, the none sentinel stays explicit`(
+        @TempDir tempDir: Path,
+    ) = runTest {
+        val store = newDataStore(tempDir)
+        val prefs = SettingsPrefs(store)
+        // Only "none" deliberately means an explicit no-reminder override; a
+        // value with no valid minutes is garbage and must drop its entry so the
+        // calendar inherits the global default instead of silently losing
+        // reminders. Partially-valid values keep their salvageable minutes.
+        store.updateData { p ->
+            val m = p.toMutablePreferences()
+            m[SettingsPrefs.CALENDAR_REMINDER_OVERRIDE_KEY] = "5=none;7=abc;8=;9=30,abc;11=15"
+            m
+        }
+        assertThat(prefs.perCalendarReminderOverride.first()).containsExactly(
+            5L, emptyList<Int>(), 9L, listOf(30), 11L, listOf(15),
+        )
+    }
+
     @Test
     fun `all-day default round-trips, including none`(@TempDir tempDir: Path) = runTest {
         val prefs = SettingsPrefs(newDataStore(tempDir))
@@ -402,6 +439,19 @@ class SettingsPrefsTest {
         assertThat(prefs.snoozeMinutes.first()).isEqualTo(1)
     }
 
+    @Test
+    fun `custom-font stamps default to zero and bump per role independently`(@TempDir tempDir: Path) = runTest {
+        val prefs = SettingsPrefs(newDataStore(tempDir))
+        // Existing installs have no stamp key — that must read as 0.
+        assertThat(prefs.brandFontStamp.first()).isEqualTo(0)
+        assertThat(prefs.plainFontStamp.first()).isEqualTo(0)
+        prefs.bumpCustomFontStamp(FontRole.BRAND)
+        prefs.bumpCustomFontStamp(FontRole.BRAND)
+        prefs.bumpCustomFontStamp(FontRole.PLAIN)
+        assertThat(prefs.brandFontStamp.first()).isEqualTo(2)
+        assertThat(prefs.plainFontStamp.first()).isEqualTo(1)
+    }
+
     @Test
     fun `explicit week-start prefs resolve regardless of locale`() {
         assertThat(WeekStartPref.Day(DayOfWeek.MONDAY).resolveFirstDay(Locale.US))

app/src/test/java/de/jeanlucmakiola/calendula/ui/theme/FontsTest.kt

@@ -20,6 +20,15 @@ class FontsTest {
         assertThat(BundledFont.fromToken(null)).isNull()
     }
 
+    @Test
+    fun `a bumped custom-font stamp breaks font-settings equality`() {
+        // Re-importing keeps the same "custom" token, so only the stamp can make
+        // the settings re-emit and invalidate remember() keys downstream.
+        val before = AppFontSettings(brand = FONT_CUSTOM_TOKEN, brandStamp = 1)
+        assertThat(before.copy(brandStamp = 2)).isNotEqualTo(before)
+        assertThat(before.copy(plainStamp = 1)).isNotEqualTo(before)
+    }
+
     @Test
     fun `system for both roles returns the untouched default typography`() {
         assertThat(calendulaTypography(brand = null, plain = null))