fix(store): three defects the instrumented suite found on first run

- forking an occurrence copied the master's alarm row id and hit the
  primary key; replaceForTask now clears it
- a sub-second DTSTART made lib-recur emit the anchor and its truncated
  self, doubling a series' first occurrence; floor to the second, which
  is all RFC 5545 DATE-TIME carries
- room-testing needs kotlinx-serialization 1.8+, but consistent
  resolution pinned androidTest to the app's 1.7.3

Tests: 52 pass on device.

app/build.gradle.kts

@@ -149,6 +149,14 @@ ksp {
 }
 
 dependencies {
+    // Not a dependency we use directly — lifecycle already drags it in at 1.7.3.
+    // AGP's consistent resolution then pins androidTest to the app classpath, and
+    // room-testing's MigrationTestHelper needs 1.8+ to deserialize the exported
+    // schema; on 1.7.3 it dies with an AbstractMethodError. Raise it in one place.
+    constraints {
+        implementation(libs.kotlinx.serialization.json)
+    }
+
     implementation(libs.androidx.core.ktx)
     implementation(libs.androidx.appcompat)
     implementation(libs.androidx.lifecycle.runtime.ktx)

app/src/androidTest/java/de/jeanlucmakiola/agendula/data/tasks/room/RoomTasksDataSourceTest.kt

@@ -27,7 +27,8 @@ class RoomTasksDataSourceTest {
     private lateinit var source: RoomTasksDataSource
     private var listId = 0L
 
-    private val now get() = Clock.System.now()
+    /** Truncated to the store's granularity: instants are columns of epoch millis. */
+    private val now get() = Instant.fromEpochMilliseconds(Clock.System.now().toEpochMilliseconds())
 
     @Before
     fun setUp() {
@@ -146,14 +147,38 @@ class RoomTasksDataSourceTest {
     fun anOverrideReplacesOnlyItsOwnOccurrence() {
         val id = source.insertTask(form(title = "Water the plants"))
         makeRecurring(id, now)
-        val before = source.tasks(TaskQuery(listId = listId)).filter { it.taskId == id }
+        // The list holds this series alone, so no filter is needed — and none can
+        // be written on taskId, since the override reports its own row id.
+        val before = source.tasks(TaskQuery(listId = listId))
         val target = before.first { it.distanceFromCurrent == 1 }
 
         source.updateInstance(id, target.occurrenceStart!!, form(title = "Water them twice"))
 
-        val after = source.tasks(TaskQuery(listId = listId)).filter { it.taskId == id }
+        val after = source.tasks(TaskQuery(listId = listId))
         assertThat(after).hasSize(before.size)
-        assertThat(after.filter { it.title == "Water them twice" }).hasSize(1)
+        val edited = after.single { it.title == "Water them twice" }
+        assertThat(edited.occurrenceStart).isEqualTo(target.occurrenceStart)
+        assertThat(after.filter { it.occurrenceStart == target.occurrenceStart }).hasSize(1)
+    }
+
+    /**
+     * An edited occurrence addresses its own row, not the master's. That is what
+     * sends the *next* edit down `updateTask` rather than forking a second time:
+     * an override carries no rule, so it reads back as non-recurring.
+     */
+    @Test
+    fun anEditedOccurrenceReportsTheOverridesOwnId() {
+        val id = source.insertTask(form(title = "Water the plants"))
+        makeRecurring(id, now)
+        val target = source.tasks(TaskQuery(listId = listId)).first { it.distanceFromCurrent == 1 }
+
+        source.updateInstance(id, target.occurrenceStart!!, form(title = "Water them twice"))
+
+        val edited = source.tasks(TaskQuery(listId = listId)).single { it.title == "Water them twice" }
+        val overrideId = db.tasks().override(id, target.occurrenceStart)!!.id
+        assertThat(edited.taskId).isEqualTo(overrideId)
+        assertThat(edited.taskId).isNotEqualTo(id)
+        assertThat(source.task(overrideId)!!.isRecurring).isFalse()
     }
 
     @Test

app/src/main/java/de/jeanlucmakiola/agendula/data/tasks/room/TaskAlarmDao.kt

@@ -22,10 +22,14 @@ interface TaskAlarmDao {
     @Query("DELETE FROM task_alarms WHERE task_id = :taskId")
     fun deleteForTask(taskId: Long): Int
 
-    /** Set the task's only reminder, or clear it with `null`. */
+    /**
+     * Set the task's only reminder, or clear it with `null`. The row that lands is
+     * always a new one — the id is cleared so an alarm lifted off another task
+     * (forking an occurrence copies the master's) inserts instead of colliding.
+     */
     @Transaction
     fun replaceForTask(taskId: Long, alarm: TaskAlarmEntity?) {
         deleteForTask(taskId)
-        alarm?.let { insert(it.copy(taskId = taskId)) }
+        alarm?.let { insert(it.copy(id = 0, taskId = taskId)) }
     }
 }

app/src/main/java/de/jeanlucmakiola/agendula/domain/recurrence/RecurrenceExpander.kt

@@ -9,6 +9,7 @@ import java.time.ZoneId
 import java.util.TimeZone
 import kotlin.time.Instant
 
+private const val MILLIS_PER_SECOND = 1000L
 private const val MILLIS_PER_DAY = 24L * 60 * 60 * 1000
 
 /** The rule set of one task series, as stored. All strings are raw iCalendar values. */
@@ -117,10 +118,17 @@ object RecurrenceExpander {
         return TimeZone.getTimeZone(stored ?: floatingZone)
     }
 
-    /** All-day series are date-anchored: pin the anchor to UTC midnight, as it is stored. */
+    /**
+     * All-day series are date-anchored: pin the anchor to UTC midnight, as it is
+     * stored. A timed one is floored to the second, because RFC 5545 DATE-TIME
+     * has no sub-second field — carrying millis in makes lib-recur emit the raw
+     * anchor *and* its truncated self, doubling the first occurrence, and mints
+     * `RECURRENCE-ID`s no other client could address.
+     */
     private fun anchorMillis(spec: RecurrenceSpec): Long {
         val millis = spec.anchor.toEpochMilliseconds()
-        return if (!spec.isAllDay) millis else Math.floorDiv(millis, MILLIS_PER_DAY) * MILLIS_PER_DAY
+        val unit = if (spec.isAllDay) MILLIS_PER_DAY else MILLIS_PER_SECOND
+        return Math.floorDiv(millis, unit) * unit
     }
 
     private fun ruleOf(value: String, zone: TimeZone): RecurrenceRule? = runCatching {

app/src/test/java/de/jeanlucmakiola/agendula/domain/recurrence/RecurrenceExpanderTest.kt

@@ -391,6 +391,19 @@ class RecurrenceExpanderTest {
         ).inOrder()
     }
 
+    @Test
+    fun `a sub-second anchor does not double the first occurrence`() {
+        // RFC 5545 DATE-TIME has second precision, but a task created from
+        // Clock.now() carries millis. Left un-floored, lib-recur emits the raw
+        // anchor *and* its truncated self, so the series starts twice.
+        val result = expand(spec(rrule = "FREQ=DAILY;COUNT=3", anchor = "2025-01-07T08:00:00.081Z"))
+        assertThat(result).containsExactly(
+            "2025-01-07T08:00:00Z",
+            "2025-01-08T08:00:00Z",
+            "2025-01-09T08:00:00Z",
+        ).inOrder()
+    }
+
     @Test
     fun `a window that ends before the anchor yields nothing`() {
         val result = expand(

gradle/libs.versions.toml

@@ -15,6 +15,7 @@ material3 = "1.5.0-alpha21"
 datastore = "1.2.1"
 # Room — Agendula's own task store (docs/OWN-STORE.md).
 room = "2.8.4"
+kotlinxSerialization = "1.8.1"
 # SAF directory writing for export/backup (DocumentFile).
 documentfile = "1.1.0"
 junit = "6.1.0"
@@ -78,6 +79,7 @@ androidx-room-runtime = { group = "androidx.room", name = "room-runtime", versio
 androidx-room-ktx = { group = "androidx.room", name = "room-ktx", version.ref = "room" }
 androidx-room-compiler = { group = "androidx.room", name = "room-compiler", version.ref = "room" }
 androidx-room-testing = { group = "androidx.room", name = "room-testing", version.ref = "room" }
+kotlinx-serialization-json = { group = "org.jetbrains.kotlinx", name = "kotlinx-serialization-json", version.ref = "kotlinxSerialization" }
 
 # DataStore
 androidx-datastore-preferences = { group = "androidx.datastore", name = "datastore-preferences", version.ref = "datastore" }