fix: tighten GitStatusIndex initial-scan and pill warming UX

Two issues from a follow-up audit on the Git Repository screen.

- Move the initial cache scan into flow `onStart` so the
  newEventBundles collector is attached before scanning. Closes a small
  race window where status events emitted between scan completion and
  collect attachment would have been dropped.

- Distinguish "index warming up" from "no status exists" by typing the
  StateFlow as `Map?` (null until first scan completes). The pill now
  hides itself entirely while warming, instead of briefly rendering
  the `defaultIfMissing` fallback and then flipping to the real status.

Also drops the dead public `rememberLatestStatus` helper and the
unnecessary derivedStateOf scaffolding — at the scale this screen
operates (tens of pills), the straightforward map read is fine.

amethyst/src/main/java/com/vitorpamplona/amethyst/model/GitStatusIndex.kt

@@ -28,6 +28,7 @@ import kotlinx.coroutines.SupervisorJob
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
 import kotlinx.coroutines.flow.asStateFlow
+import kotlinx.coroutines.flow.onStart
 import kotlinx.coroutines.launch
 import java.util.concurrent.atomic.AtomicBoolean
 
@@ -42,38 +43,40 @@ object GitStatusIndex {
     private val scope = CoroutineScope(Dispatchers.IO + SupervisorJob())
     private val started = AtomicBoolean(false)
 
-    private val mutableLatestByTarget = MutableStateFlow<Map<HexKey, GitStatusEvent>>(emptyMap())
-    val latestByTarget: StateFlow<Map<HexKey, GitStatusEvent>> = mutableLatestByTarget.asStateFlow()
+    private val mutableLatestByTarget = MutableStateFlow<Map<HexKey, GitStatusEvent>?>(null)
+    val latestByTarget: StateFlow<Map<HexKey, GitStatusEvent>?> = mutableLatestByTarget.asStateFlow()
 
     fun startIfNeeded() {
         if (!started.compareAndSet(false, true)) return
         scope.launch {
-            val initial = HashMap<HexKey, GitStatusEvent>()
-            LocalCache.notes.forEach { _, note ->
-                val event = note.event as? GitStatusEvent ?: return@forEach
-                val target = event.rootEventId() ?: return@forEach
-                val current = initial[target]
-                if (current == null || event.createdAt > current.createdAt) {
-                    initial[target] = event
-                }
-            }
-            mutableLatestByTarget.value = initial
-
-            LocalCache.live.newEventBundles.collect { bundle ->
-                processBundle(bundle)
-            }
+            // Subscribe to bundle updates BEFORE the initial scan via onStart, so any
+            // events that arrive between scan start and collector attach are picked up.
+            LocalCache.live.newEventBundles
+                .onStart {
+                    val initial = HashMap<HexKey, GitStatusEvent>()
+                    LocalCache.notes.forEach { _, note ->
+                        val event = note.event as? GitStatusEvent ?: return@forEach
+                        val target = event.rootEventId() ?: return@forEach
+                        val current = initial[target]
+                        if (current == null || event.createdAt > current.createdAt) {
+                            initial[target] = event
+                        }
+                    }
+                    mutableLatestByTarget.value = initial
+                }.collect { bundle -> processBundle(bundle) }
         }
     }
 
     private fun processBundle(bundle: Set<Note>) {
+        val snapshot = mutableLatestByTarget.value ?: emptyMap()
         var modified: HashMap<HexKey, GitStatusEvent>? = null
         for (note in bundle) {
             val event = note.event as? GitStatusEvent ?: continue
             val target = event.rootEventId() ?: continue
-            val map = modified ?: mutableLatestByTarget.value
+            val map = modified ?: snapshot
             val current = map[target]
             if (current == null || event.createdAt > current.createdAt) {
-                if (modified == null) modified = HashMap(mutableLatestByTarget.value)
+                if (modified == null) modified = HashMap(snapshot)
                 modified[target] = event
             }
         }

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/note/types/GitStatusPill.kt

@@ -30,9 +30,7 @@ import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
-import androidx.compose.runtime.derivedStateOf
 import androidx.compose.runtime.getValue
-import androidx.compose.runtime.remember
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.clip
@@ -70,23 +68,16 @@ private fun GitStatusEvent.statusKind(): StatusKind =
         else -> StatusKind.OPEN
     }
 
-@Composable
-fun rememberLatestStatus(targetIdHex: String): GitStatusEvent? {
-    LaunchedEffect(Unit) { GitStatusIndex.startIfNeeded() }
-    val index by GitStatusIndex.latestByTarget.collectAsStateWithLifecycle()
-    val latest by remember(targetIdHex) { derivedStateOf { index[targetIdHex] } }
-    return latest
-}
-
 @Composable
 fun GitStatusPill(
     targetIdHex: String,
     modifier: Modifier = Modifier,
     defaultIfMissing: StatusKind? = null,
 ) {
-    val latest = rememberLatestStatus(targetIdHex)
-    val kind =
-        latest?.statusKind() ?: defaultIfMissing ?: return
+    LaunchedEffect(Unit) { GitStatusIndex.startIfNeeded() }
+    val index by GitStatusIndex.latestByTarget.collectAsStateWithLifecycle()
+    val map = index ?: return // hide pill until the initial scan completes — avoids a default-then-real flicker
+    val kind = map[targetIdHex]?.statusKind() ?: defaultIfMissing ?: return
 
     GitStatusPill(kind, modifier)
 }