test: render every ImageComposeScene on the AWT event thread

The rare CI hang is a lock-order deadlock in Compose Multiplatform 1.8.2,
shown by the thread dump of run 40299943329:

- the test thread renders the scene and holds the FlushCoroutineDispatcher
  runLock while LazyListState.scrollToItem measures and wants the
  SnapshotStateObserver's observedScopeMapsLock;
- the AWT event thread sends the global snapshot notifications and holds
  observedScopeMapsLock in drainChanges while a re-read derived state wakes
  the scene's snapshotFlow collector, whose dispatch wants runLock.

The application renders on the event thread, where both monitors are simply
re-entered. The tests now do the same: onEventThread builds, renders and
closes each scene there and rethrows what the block throws.

Claude-Session: https://claude.ai/code/session_01FJBfPYm6rCH4zD6T7bcC7Y

app-desktop/src/test/kotlin/kst4contest/view/compose/CompactControlsVisualRenderingTest.kt

@@ -55,6 +55,7 @@ class CompactControlsVisualRenderingTest(@param:TempDir private val tempDir: Pat
         }
         val filters = StationFilterState()
 
+        return onEventThread {
             val scene = ImageComposeScene(width = 1366, height = 380, density = Density(scale)) {
                 Kst4ContestTheme(darkMode = darkMode, baseFontSizeSp = 12f) {
                     Surface(
@@ -90,12 +91,13 @@ class CompactControlsVisualRenderingTest(@param:TempDir private val tempDir: Pat
                     }
                 }
             }
-        return try {
+            try {
                 scene.render().encodeToData()!!.bytes
             } finally {
                 scene.close()
             }
         }
+    }
 
     private class RenderActions(private val preferences: ChatPreferences) : ChatInputActions {
         override fun panelSelection(): ChatMember? = null

app-desktop/src/test/kotlin/kst4contest/view/compose/OnEventThread.kt

@@ -0,0 +1,37 @@
+package kst4contest.view.compose
+
+import java.awt.EventQueue
+import java.lang.reflect.InvocationTargetException
+
+/*
+ * An ImageComposeScene must live on the AWT event thread, the thread the application renders
+ * on. Compose Multiplatform 1.8.2 sends the global snapshot notifications there
+ * (GlobalSnapshotManager), and doing so takes two locks in the opposite order from a render
+ * on any other thread:
+ *
+ *  - the render holds the scene's FlushCoroutineDispatcher runLock while a task it runs
+ *    (here LazyListState.scrollToItem) measures and wants the SnapshotStateObserver's
+ *    observedScopeMapsLock;
+ *  - the event thread holds observedScopeMapsLock in drainChanges while a derived state it
+ *    re-reads wakes a snapshotFlow collector of that scene, whose dispatch wants runLock.
+ *
+ * Both waited forever in CI runs 40252077018, 40252089738 and 40299943329; the thread dump of
+ * the last one shows both stacks. On one thread the two monitors are simply re-entered, which
+ * is why the application never hangs this way.
+ */
+
+/**
+ * Runs [block] on the AWT event thread, waits for it and returns its result. Whatever
+ * [block] throws is rethrown here unwrapped, so a failed assertion still reads as one.
+ */
+internal fun <T> onEventThread(block: () -> T): T {
+    if (EventQueue.isDispatchThread()) return block()
+
+    var result: Result<T>? = null
+    try {
+        EventQueue.invokeAndWait { result = runCatching(block) }
+    } catch (wrapped: InvocationTargetException) {
+        throw wrapped.cause ?: wrapped
+    }
+    return result!!.getOrThrow()
+}

app-desktop/src/test/kotlin/kst4contest/view/compose/SelectedStationMessageUiVisualRenderingTest.kt

@@ -84,6 +84,7 @@ class SelectedStationMessageUiVisualRenderingTest {
             replaceRows(listOf(message(member("DL1ABC", 2), member("DL2XYZ", 2), "pse sked")))
         }
 
+        return onEventThread {
             val scene = ImageComposeScene(width = 1366, height = windowHeight, density = Density(scale)) {
                 Kst4ContestTheme(darkMode = darkMode, baseFontSizeSp = 12f) {
                     Surface(
@@ -111,12 +112,13 @@ class SelectedStationMessageUiVisualRenderingTest {
                 }
             }
 
-        return try {
+            try {
                 scene.render().encodeToData()!!.bytes
             } finally {
                 scene.close()
             }
         }
+    }
 
     private fun messageTable() = DataTableState(
         columns = listOf(

app-desktop/src/test/kotlin/kst4contest/view/compose/StationWorkspaceVisualRenderingTest.kt

@@ -87,6 +87,7 @@ class StationWorkspaceVisualRenderingTest {
             RowKeys.byReference<ChatMessage>(),
         )
 
+        return onEventThread {
             val scene = ImageComposeScene(
                 width = 1366,
                 height = scenario.height,
@@ -139,12 +140,13 @@ class StationWorkspaceVisualRenderingTest {
                 }
             }
 
-        return try {
+            try {
                 scene.render().encodeToData()!!.bytes
             } finally {
                 scene.close()
             }
         }
+    }
 
     private fun member(callSign: String, category: Int) = ChatMember().apply {
         this.callSign = callSign

app-desktop/src/test/kotlin/kst4contest/view/compose/TopPriorityCandidatesWindowTest.kt

@@ -32,6 +32,7 @@ class TopPriorityCandidatesWindowTest {
     /** Runs [block] against a rendered list of [twoCandidates] and reports what it picked. */
     private fun picking(block: (ImageComposeScene) -> Unit): String? {
         var picked: String? = null
+        onEventThread {
             val scene = ImageComposeScene(width = 360, height = 500, density = Density(1f)) {
                 TopPriorityCandidatesWindow.CandidateListForTest(twoCandidates) {
                     picked = it.displayCallSign
@@ -44,6 +45,7 @@ class TopPriorityCandidatesWindowTest {
             } finally {
                 scene.close()
             }
+        }
         return picked
     }
 
@@ -78,6 +80,7 @@ class TopPriorityCandidatesWindowTest {
     @Test
     fun `the list renders with candidates and without`() {
         listOf(emptyList(), twoCandidates).forEach { ranking ->
+            onEventThread {
                 val scene = ImageComposeScene(width = 360, height = 500, density = Density(1f)) {
                     TopPriorityCandidatesWindow.CandidateListForTest(ranking) { }
                 }
@@ -88,6 +91,7 @@ class TopPriorityCandidatesWindowTest {
                 }
             }
         }
+    }
 
     /**
      * A double click picks the candidate under it, and picks the right one.

app-desktop/src/test/kotlin/kst4contest/view/compose/map/ComposeStationMapDrawingTest.kt

@@ -4,6 +4,7 @@ import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.ui.ImageComposeScene
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.unit.Density
+import kst4contest.view.compose.onEventThread
 import kst4contest.view.map.MapCallsignRawSnapshot
 import kst4contest.view.map.MapViewport
 import kst4contest.view.map.TileFetcher
@@ -71,6 +72,7 @@ class ComposeStationMapDrawingTest {
         workedGrossFields: Set<String> = emptySet(),
         darkMode: Boolean = true,
     ): BufferedImage {
+        return onEventThread {
             val scene = ImageComposeScene(canvasWidth, canvasHeight, Density(1f)) {
                 ComposeStationMap(
                     markers = markers,
@@ -89,11 +91,12 @@ class ComposeStationMapDrawingTest {
                 )
             }
             try {
-            return ImageIO.read(ByteArrayInputStream(scene.render().encodeToData()!!.bytes))
+                ImageIO.read(ByteArrayInputStream(scene.render().encodeToData()!!.bytes))
             } finally {
                 scene.close()
             }
         }
+    }
 
     private fun countColour(image: BufferedImage, rgb: Int): Int {
         var count = 0

app-desktop/src/test/kotlin/kst4contest/view/compose/map/ComposeStationMapLayoutTest.kt

@@ -4,6 +4,7 @@ import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.ui.ImageComposeScene
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.unit.Density
+import kst4contest.view.compose.onEventThread
 import kst4contest.view.map.MapCallsignRawSnapshot
 import kst4contest.view.map.TileFetcher
 import org.junit.jupiter.api.Test
@@ -33,6 +34,7 @@ class ComposeStationMapLayoutTest {
     )
 
     private fun renderAt(widthPx: Int, heightPx: Int, zoom: Float) {
+        onEventThread {
             val scene = ImageComposeScene(
                 width = widthPx,
                 height = heightPx,
@@ -59,6 +61,7 @@ class ComposeStationMapLayoutTest {
                 scene.close()
             }
         }
+    }
 
     @Test
     fun `renders at a normal window size and integer zoom`() = renderAt(900, 600, 6f)

app-desktop/src/test/kotlin/kst4contest/view/compose/map/PathAnalysisDetailsLayoutTest.kt

@@ -4,6 +4,7 @@ import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.ui.ImageComposeScene
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.unit.Density
+import kst4contest.view.compose.onEventThread
 import kst4contest.view.map.PathAnalysisResult
 import org.junit.jupiter.api.Test
 
@@ -25,6 +26,7 @@ class PathAnalysisDetailsLayoutTest {
     private val narrowWidthPx = 120
 
     private fun renderAt(widthPx: Int, result: PathAnalysisResult?) {
+        onEventThread {
             val scene = ImageComposeScene(
                 width = widthPx,
                 height = 600,
@@ -42,6 +44,7 @@ class PathAnalysisDetailsLayoutTest {
                 scene.close()
             }
         }
+    }
 
     @Test
     fun `renders when the column is narrower than the assessment label`() {

app-desktop/src/test/kotlin/kst4contest/view/compose/map/PathAnalysisDetailsWidthTest.kt

@@ -4,6 +4,7 @@ import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.ui.ImageComposeScene
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.unit.Density
+import kst4contest.view.compose.onEventThread
 import kst4contest.view.map.PathAnalysisResult
 import org.junit.jupiter.api.Assertions.assertTrue
 import org.junit.jupiter.api.Test
@@ -31,6 +32,7 @@ class PathAnalysisDetailsWidthTest {
     private val assessmentBackground = 0x33383E
 
     private fun render(paneWidthPx: Int, heightPx: Int = 600): BufferedImage {
+        return onEventThread {
             val scene = ImageComposeScene(width = paneWidthPx, height = heightPx, density = Density(1f)) {
                 PathAnalysisDetails(
                     result = PathAnalysisResult.loading("JO50JP", "JN24JB", "F5JMI"),
@@ -40,11 +42,12 @@ class PathAnalysisDetailsWidthTest {
             }
             try {
                 val png = scene.render().encodeToData()!!.bytes
-            return ImageIO.read(ByteArrayInputStream(png))
+                ImageIO.read(ByteArrayInputStream(png))
             } finally {
                 scene.close()
             }
         }
+    }
 
     /** The smallest x at which the assessment background appears, or -1 when it does not. */
     private fun assessmentLeftEdge(image: BufferedImage): Int {

app-desktop/src/test/kotlin/kst4contest/view/compose/map/PathProfileChartLayoutTest.kt

@@ -4,6 +4,7 @@ import androidx.compose.foundation.layout.fillMaxSize
 import androidx.compose.ui.ImageComposeScene
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.unit.Density
+import kst4contest.view.compose.onEventThread
 import org.junit.jupiter.api.Test
 
 /**
@@ -18,6 +19,7 @@ import org.junit.jupiter.api.Test
 class PathProfileChartLayoutTest {
 
     private fun renderAt(widthPx: Int, heightPx: Int) {
+        onEventThread {
             val scene = ImageComposeScene(
                 width = widthPx,
                 height = heightPx,
@@ -31,6 +33,7 @@ class PathProfileChartLayoutTest {
                 scene.close()
             }
         }
+    }
 
     @Test
     fun `renders at the height the window gives it`() = renderAt(800, 210)

app-desktop/src/test/kotlin/kst4contest/view/compose/map/StationMapBodyLayoutTest.kt

@@ -15,6 +15,7 @@ import androidx.compose.ui.unit.dp
 import kst4contest.view.compose.SplitterOrientation
 import kst4contest.view.compose.SplitterPane
 import kst4contest.view.compose.SplitterState
+import kst4contest.view.compose.onEventThread
 import kst4contest.view.map.MapCallsignRawSnapshot
 import kst4contest.view.map.PathAnalysisResult
 import kst4contest.view.map.TileFetcher
@@ -88,6 +89,7 @@ class StationMapBodyLayoutTest {
     }
 
     private fun renderAt(widthPx: Int, heightPx: Int, pathAnalysisVisible: Boolean = true) {
+        onEventThread {
             val scene = ImageComposeScene(width = widthPx, height = heightPx, density = Density(1f)) {
                 Body(pathAnalysisVisible)
             }
@@ -97,6 +99,7 @@ class StationMapBodyLayoutTest {
                 scene.close()
             }
         }
+    }
 
     @Test
     fun `renders at the window's minimum size`() = renderAt(900, 600)