feat(media): lightbox overlay with zoom, gallery navigation, and save

Phase 5: Full-screen lightbox overlay with mouse wheel zoom + pan,
left/right gallery carousel, keyboard shortcuts (Esc/arrows/Ctrl+S),
save to disk via FileDialog. Images in NoteCard are clickable.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/ui/FeedScreen.kt

@@ -75,6 +75,7 @@ import com.vitorpamplona.amethyst.desktop.subscriptions.createRepliesSubscriptio
 import com.vitorpamplona.amethyst.desktop.subscriptions.createRepostsSubscription
 import com.vitorpamplona.amethyst.desktop.subscriptions.createZapsSubscription
 import com.vitorpamplona.amethyst.desktop.subscriptions.rememberSubscription
+import com.vitorpamplona.amethyst.desktop.ui.media.LightboxOverlay
 import com.vitorpamplona.amethyst.desktop.ui.note.NoteCard
 import com.vitorpamplona.quartz.nip01Core.core.Event
 import com.vitorpamplona.quartz.nip01Core.metadata.MetadataEvent
@@ -100,6 +101,7 @@ fun FeedNoteCard(
     onZapFeedback: (ZapFeedback) -> Unit,
     onNavigateToProfile: (String) -> Unit = {},
     onNavigateToThread: (String) -> Unit = {},
+    onImageClick: ((List<String>, Int) -> Unit)? = null,
     zapReceipts: List<ZapReceipt> = emptyList(),
     reactionCount: Int = 0,
     replyCount: Int = 0,
@@ -119,6 +121,7 @@ fun FeedNoteCard(
         NoteCard(
             note = event.toNoteDisplayData(localCache),
             onAuthorClick = onNavigateToProfile,
+            onImageClick = onImageClick,
         )
 
         // Action buttons (only if logged in)
@@ -180,6 +183,7 @@ fun FeedScreen(
         }
     val events by eventState.items.collectAsState()
     var replyToEvent by remember { mutableStateOf<Event?>(null) }
+    var lightboxState by remember { mutableStateOf<Pair<List<String>, Int>?>(null) }
     var feedMode by remember { mutableStateOf(initialFeedMode ?: DesktopPreferences.feedMode) }
     var followedUsers by remember { mutableStateOf<Set<String>>(emptySet()) }
     var zapsByEvent by remember { mutableStateOf<Map<String, List<ZapReceipt>>>(emptyMap()) }
@@ -601,6 +605,7 @@ fun FeedScreen(
                         onZapFeedback = onZapFeedback,
                         onNavigateToProfile = onNavigateToProfile,
                         onNavigateToThread = onNavigateToThread,
+                        onImageClick = { urls, index -> lightboxState = urls to index },
                         zapReceipts = zapsByEvent[event.id] ?: emptyList(),
                         reactionCount = reactionsByEvent[event.id] ?: 0,
                         replyCount = repliesByEvent[event.id] ?: 0,
@@ -631,5 +636,14 @@ fun FeedScreen(
                 replyTo = replyToEvent,
             )
         }
+
+        // Lightbox overlay
+        lightboxState?.let { (urls, index) ->
+            LightboxOverlay(
+                urls = urls,
+                initialIndex = index,
+                onDismiss = { lightboxState = null },
+            )
+        }
     }
 }

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/ui/media/LightboxOverlay.kt

@@ -0,0 +1,205 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.desktop.ui.media
+
+import androidx.compose.foundation.background
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.interaction.MutableInteractionSource
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.automirrored.filled.ArrowBack
+import androidx.compose.material.icons.automirrored.filled.ArrowForward
+import androidx.compose.material.icons.filled.Close
+import androidx.compose.material.icons.filled.Save
+import androidx.compose.material3.Icon
+import androidx.compose.material3.IconButton
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Text
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.LaunchedEffect
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableIntStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.rememberCoroutineScope
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.focus.FocusRequester
+import androidx.compose.ui.focus.focusRequester
+import androidx.compose.ui.graphics.Color
+import androidx.compose.ui.input.key.Key
+import androidx.compose.ui.input.key.KeyEventType
+import androidx.compose.ui.input.key.isCtrlPressed
+import androidx.compose.ui.input.key.key
+import androidx.compose.ui.input.key.onKeyEvent
+import androidx.compose.ui.input.key.type
+import androidx.compose.ui.unit.dp
+import kotlinx.coroutines.launch
+
+@Composable
+fun LightboxOverlay(
+    urls: List<String>,
+    initialIndex: Int = 0,
+    onDismiss: () -> Unit,
+    modifier: Modifier = Modifier,
+) {
+    var currentIndex by remember { mutableIntStateOf(initialIndex.coerceIn(0, urls.lastIndex)) }
+    val scope = rememberCoroutineScope()
+    val focusRequester = remember { FocusRequester() }
+
+    LaunchedEffect(Unit) {
+        focusRequester.requestFocus()
+    }
+
+    Box(
+        modifier =
+            modifier
+                .fillMaxSize()
+                .background(Color.Black.copy(alpha = 0.9f))
+                .focusRequester(focusRequester)
+                .onKeyEvent { event ->
+                    if (event.type != KeyEventType.KeyDown) return@onKeyEvent false
+                    when (event.key) {
+                        Key.Escape -> {
+                            onDismiss()
+                            true
+                        }
+
+                        Key.DirectionLeft -> {
+                            if (currentIndex > 0) currentIndex--
+                            true
+                        }
+
+                        Key.DirectionRight -> {
+                            if (currentIndex < urls.lastIndex) currentIndex++
+                            true
+                        }
+
+                        Key.S -> {
+                            if (event.isCtrlPressed) {
+                                scope.launch {
+                                    SaveMediaAction.saveMedia(urls[currentIndex])
+                                }
+                                true
+                            } else {
+                                false
+                            }
+                        }
+
+                        else -> {
+                            false
+                        }
+                    }
+                }.clickable(
+                    interactionSource = remember { MutableInteractionSource() },
+                    indication = null,
+                ) {
+                    // Click on backdrop doesn't close — use X button or Esc
+                },
+    ) {
+        // Main image
+        ZoomableImage(
+            url = urls[currentIndex],
+            modifier = Modifier.fillMaxSize().padding(48.dp),
+        )
+
+        // Top bar
+        Row(
+            modifier =
+                Modifier
+                    .fillMaxWidth()
+                    .align(Alignment.TopCenter)
+                    .background(Color.Black.copy(alpha = 0.5f))
+                    .padding(8.dp),
+            horizontalArrangement = Arrangement.SpaceBetween,
+            verticalAlignment = Alignment.CenterVertically,
+        ) {
+            if (urls.size > 1) {
+                Text(
+                    "${currentIndex + 1} / ${urls.size}",
+                    color = Color.White,
+                    style = MaterialTheme.typography.bodyMedium,
+                )
+            }
+
+            Row {
+                IconButton(
+                    onClick = {
+                        scope.launch {
+                            SaveMediaAction.saveMedia(urls[currentIndex])
+                        }
+                    },
+                ) {
+                    Icon(
+                        Icons.Default.Save,
+                        contentDescription = "Save",
+                        tint = Color.White,
+                    )
+                }
+
+                IconButton(onClick = onDismiss) {
+                    Icon(
+                        Icons.Default.Close,
+                        contentDescription = "Close",
+                        tint = Color.White,
+                    )
+                }
+            }
+        }
+
+        // Navigation arrows
+        if (urls.size > 1) {
+            if (currentIndex > 0) {
+                IconButton(
+                    onClick = { currentIndex-- },
+                    modifier = Modifier.align(Alignment.CenterStart).padding(16.dp),
+                ) {
+                    Icon(
+                        Icons.AutoMirrored.Filled.ArrowBack,
+                        contentDescription = "Previous",
+                        tint = Color.White,
+                        modifier = Modifier.size(48.dp),
+                    )
+                }
+            }
+
+            if (currentIndex < urls.lastIndex) {
+                IconButton(
+                    onClick = { currentIndex++ },
+                    modifier = Modifier.align(Alignment.CenterEnd).padding(16.dp),
+                ) {
+                    Icon(
+                        Icons.AutoMirrored.Filled.ArrowForward,
+                        contentDescription = "Next",
+                        tint = Color.White,
+                        modifier = Modifier.size(48.dp),
+                    )
+                }
+            }
+        }
+    }
+}

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/ui/media/SaveMediaAction.kt

@@ -0,0 +1,70 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.desktop.ui.media
+
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.withContext
+import okhttp3.OkHttpClient
+import okhttp3.Request
+import java.awt.FileDialog
+import java.awt.Frame
+import java.io.File
+
+object SaveMediaAction {
+    private val httpClient = OkHttpClient()
+
+    /**
+     * Opens a save dialog and downloads the media URL to the chosen file.
+     * Returns the saved file path or null if cancelled/failed.
+     */
+    suspend fun saveMedia(
+        url: String,
+        suggestedFilename: String? = null,
+    ): File? =
+        withContext(Dispatchers.IO) {
+            val filename = suggestedFilename ?: url.substringAfterLast('/').substringBefore('?').ifBlank { "media" }
+
+            val dialog =
+                FileDialog(null as Frame?, "Save Media", FileDialog.SAVE).apply {
+                    file = filename
+                }
+            dialog.isVisible = true
+
+            val dir = dialog.directory ?: return@withContext null
+            val file = File(dir, dialog.file ?: return@withContext null)
+
+            try {
+                val request = Request.Builder().url(url).build()
+                val response = httpClient.newCall(request).execute()
+                response.use { resp ->
+                    if (!resp.isSuccessful) return@withContext null
+                    resp.body.byteStream().use { input ->
+                        file.outputStream().use { output ->
+                            input.copyTo(output)
+                        }
+                    }
+                }
+                file
+            } catch (_: Exception) {
+                null
+            }
+        }
+}

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/ui/media/ZoomableImage.kt

@@ -0,0 +1,100 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.desktop.ui.media
+
+import androidx.compose.foundation.gestures.detectDragGestures
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableFloatStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.ExperimentalComposeUiApi
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.graphics.graphicsLayer
+import androidx.compose.ui.input.pointer.PointerEventType
+import androidx.compose.ui.input.pointer.pointerInput
+import androidx.compose.ui.layout.ContentScale
+import coil3.compose.AsyncImage
+
+@OptIn(ExperimentalComposeUiApi::class)
+@Composable
+fun ZoomableImage(
+    url: String,
+    modifier: Modifier = Modifier,
+    onDoubleClick: (() -> Unit)? = null,
+) {
+    var scale by remember { mutableFloatStateOf(1f) }
+    var offsetX by remember { mutableFloatStateOf(0f) }
+    var offsetY by remember { mutableFloatStateOf(0f) }
+
+    Box(
+        modifier =
+            modifier
+                .fillMaxSize()
+                .pointerInput(Unit) {
+                    awaitPointerEventScope {
+                        while (true) {
+                            val event = awaitPointerEvent()
+                            if (event.type == PointerEventType.Scroll) {
+                                val scrollDelta =
+                                    event.changes
+                                        .firstOrNull()
+                                        ?.scrollDelta
+                                        ?.y ?: 0f
+                                val zoomFactor = if (scrollDelta > 0) 0.9f else 1.1f
+                                scale = (scale * zoomFactor).coerceIn(0.5f, 10f)
+                                event.changes.forEach { it.consume() }
+                            }
+                        }
+                    }
+                }.pointerInput(Unit) {
+                    detectDragGestures { _, dragAmount ->
+                        if (scale > 1f) {
+                            offsetX += dragAmount.x
+                            offsetY += dragAmount.y
+                        }
+                    }
+                },
+        contentAlignment = Alignment.Center,
+    ) {
+        AsyncImage(
+            model = url,
+            contentDescription = null,
+            modifier =
+                Modifier
+                    .fillMaxSize()
+                    .graphicsLayer(
+                        scaleX = scale,
+                        scaleY = scale,
+                        translationX = offsetX,
+                        translationY = offsetY,
+                    ),
+            contentScale = ContentScale.Fit,
+        )
+    }
+}
+
+fun resetZoom(onReset: () -> Unit) {
+    onReset()
+}

desktopApp/src/jvmMain/kotlin/com/vitorpamplona/amethyst/desktop/ui/note/NoteCard.kt

@@ -78,6 +78,7 @@ fun NoteCard(
     modifier: Modifier = Modifier,
     onClick: (() -> Unit)? = null,
     onAuthorClick: ((String) -> Unit)? = null,
+    onImageClick: ((List<String>, Int) -> Unit)? = null,
 ) {
     val urls = remember(note.content) { UrlParser().parseValidUrls(note.content) }
     val imageUrls =
@@ -173,7 +174,7 @@ fun NoteCard(
                 if (strippedContent.isNotBlank()) {
                     Spacer(Modifier.height(8.dp))
                 }
-                for (url in imageUrls) {
+                for ((index, url) in imageUrls.withIndex()) {
                     AsyncImage(
                         model = url,
                         contentDescription = null,
@@ -181,7 +182,14 @@ fun NoteCard(
                             Modifier
                                 .fillMaxWidth()
                                 .heightIn(max = 400.dp)
-                                .clip(RoundedCornerShape(8.dp)),
+                                .clip(RoundedCornerShape(8.dp))
+                                .then(
+                                    if (onImageClick != null) {
+                                        Modifier.clickable { onImageClick(imageUrls, index) }
+                                    } else {
+                                        Modifier
+                                    },
+                                ),
                         contentScale = ContentScale.FillWidth,
                     )
                     if (url != imageUrls.last()) {