Android recent tags: reuse ui/Time.kt's epochMillis (#5931)

RecentTags.kt declared a second epochMillis(String?): Long beside Time.kt's
epochMillis(String): Long?. A string literal resolved to the existing one, so
the test asserted 0 against its null.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

android/app/src/main/java/com/fabledsword/inkwell/ui/RecentTags.kt

@@ -10,7 +10,6 @@ import androidx.compose.ui.platform.LocalContext
 import com.fabledsword.inkwell.TagViews
 import com.fabledsword.inkwell.core.Label
 import com.fabledsword.inkwell.core.Note
-import java.time.OffsetDateTime
 
 /**
  * The drawer lists the few tags in use rather than every tag (#5931), so a long
@@ -47,17 +46,16 @@ fun tagRecency(
     notes: List<Note>,
     views: Map<String, Long>,
 ): Map<String, Long> {
-    val latest = labels.associate { it.id to maxOf(epochMillis(it.lastUsed), views[it.id] ?: 0L) }.toMutableMap()
+    // A missing or unreadable stamp counts as 0: such a tag simply ranks last.
+    val latest = labels.associate { it.id to maxOf(it.lastUsed.millis(), views[it.id] ?: 0L) }.toMutableMap()
     for (note in notes) {
-        val at = epochMillis(note.updatedAt)
+        val at = note.updatedAt.millis()
         for (label in note.labels) latest.computeIfPresent(label.id) { _, was -> maxOf(was, at) }
     }
     return latest
 }
 
-/** 0 for a missing or unreadable stamp: such a tag simply ranks last. */
-fun epochMillis(stamp: String?): Long =
-    stamp?.let { runCatching { OffsetDateTime.parse(it).toInstant().toEpochMilli() }.getOrNull() } ?: 0L
+private fun String?.millis(): Long = this?.let(::epochMillis) ?: 0L
 
 /**
  * When each tag's lens was last opened here. Opening one counts as using it,

android/app/src/test/java/com/fabledsword/inkwell/ui/RecentTagsTest.kt

@@ -1,6 +1,7 @@
 package com.fabledsword.inkwell.ui
 
 import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
 import org.junit.Assert.assertSame
 import org.junit.Test
 
@@ -32,10 +33,10 @@ class RecentTagsTest {
     }
 
     @Test
-    fun `reads both stamp forms the store holds`() {
+    fun `the shared epochMillis reads both stamp forms tag recency is built from`() {
+        // The core writes `Z` with milliseconds; a pulled server row may carry +00:00.
         assertEquals(1_760_000_000_000L, epochMillis("2025-10-09T08:53:20.000Z"))
         assertEquals(1_760_000_000_000L, epochMillis("2025-10-09T08:53:20+00:00"))
-        assertEquals(0L, epochMillis(null))
-        assertEquals(0L, epochMillis("not a time"))
+        assertNull(epochMillis("not a time"))
     }
 }