diff --git a/packages/ui/src/components/chat/message/MessageBody.tsx b/packages/ui/src/components/chat/message/MessageBody.tsx
index 8963e5fb..a697c165 100644
--- a/packages/ui/src/components/chat/message/MessageBody.tsx
+++ b/packages/ui/src/components/chat/message/MessageBody.tsx
@@ -1212,10 +1212,10 @@ const AssistantMessageBody = React.memo(({
         return visibleParts.filter((part) => part.type === 'text');
     }, [visibleParts]);
     const finalizedAssistantMarkdownContents = React.useMemo(() => (
-        isMessageCompleted && !isMobile
+        isMessageCompleted
             ? assistantTextParts.map(extractTextContent).filter((text) => text.trim().length > 0)
             : []
-    ), [assistantTextParts, isMessageCompleted, isMobile]);
+    ), [assistantTextParts, isMessageCompleted]);
     const assistantPlanText = React.useMemo(() => flattenAssistantTextParts(assistantTextParts), [assistantTextParts]);
     const suggestedPlanTitle = React.useMemo(() => suggestPlanTitleFromText(assistantPlanText), [assistantPlanText]);
 
@@ -1868,7 +1868,7 @@ const AssistantMessageBody = React.memo(({
                             chatRenderMode={chatRenderMode}
                             onContentChange={onContentChange}
                             onShowPopup={onShowPopup}
-                            enableMarkdownImages={isMessageCompleted && !isMobile}
+                            enableMarkdownImages={isMessageCompleted}
                         />
                     </div>
                 );
diff --git a/packages/ui/src/components/chat/message/ToolOutputDialog.test.ts b/packages/ui/src/components/chat/message/ToolOutputDialog.test.ts
index a0d7f916..08584eb8 100644
--- a/packages/ui/src/components/chat/message/ToolOutputDialog.test.ts
+++ b/packages/ui/src/components/chat/message/ToolOutputDialog.test.ts
@@ -1,6 +1,5 @@
 import { describe, expect, test } from 'bun:test';
 
-import { getImagePreviewBounds, getImagePreviewDialogLayout } from './imagePreviewSizing';
 import { MermaidLoadFailure, getMermaidDataUrlSourcePromise, isCurrentMermaidLoadRequest, nextMermaidLoadRequestId } from './toolOutputDialogMermaid';
 
 describe('getMermaidDataUrlSourcePromise', () => {
@@ -30,43 +29,3 @@ describe('Mermaid load request ids', () => {
         expect(isCurrentMermaidLoadRequest(secondRequest, secondRequest)).toBe(true);
     });
 });
-
-describe('Markdown image preview bounds', () => {
-    test('uses sixty percent of the viewport width with vertical containment', () => {
-        expect(getImagePreviewBounds({ width: 1200, height: 800 }, false, true)).toEqual({
-            maxWidth: 720,
-            maxHeight: 640,
-        });
-    });
-
-    test('preserves existing attachment preview bounds', () => {
-        expect(getImagePreviewBounds({ width: 1200, height: 800 }, false, false)).toEqual({
-            maxWidth: 900,
-            maxHeight: 600,
-        });
-    });
-
-    test('keeps a readable modal width for narrow portrait images', () => {
-        expect(getImagePreviewDialogLayout(
-            { width: 29, height: 576 },
-            { width: 1280, height: 720 },
-            false,
-        )).toEqual({
-            dialogWidth: 320,
-            imageWidth: 29,
-            imageHeight: 576,
-        });
-    });
-
-    test('fits image content inside the mobile dialog chrome without cropping', () => {
-        expect(getImagePreviewDialogLayout(
-            { width: 275, height: 500 },
-            { width: 320, height: 700 },
-            true,
-        )).toEqual({
-            dialogWidth: 304,
-            imageWidth: 270,
-            imageHeight: 491,
-        });
-    });
-});
diff --git a/packages/ui/src/components/chat/message/ToolOutputDialog.tsx b/packages/ui/src/components/chat/message/ToolOutputDialog.tsx
index ce01e48b..15298662 100644
--- a/packages/ui/src/components/chat/message/ToolOutputDialog.tsx
+++ b/packages/ui/src/components/chat/message/ToolOutputDialog.tsx
@@ -1,5 +1,5 @@
 import React from 'react';
-import { Dialog, DialogContent, DialogHeader, DialogTitle } from '@/components/ui/dialog';
+import { Dialog, DialogContent } from '@/components/ui/dialog';
 import { File as PierreFile, PatchDiff } from '@pierre/diffs/react';
 import { WorkerHighlightedCode } from '@/components/code/WorkerHighlightedCode';
 import { createPortal } from 'react-dom';
@@ -29,11 +29,6 @@ import { Icon } from "@/components/icon/Icon";
 import { useI18n, type I18nKey, type I18nParams } from '@/lib/i18n';
 import { runtimeFetch } from '@/lib/runtime-fetch';
 import { MermaidLoadFailure, getMermaidDataUrlSourcePromise, isCurrentMermaidLoadRequest, isMermaidLoadFailure, nextMermaidLoadRequestId } from './toolOutputDialogMermaid';
-import {
-    getImagePreviewBounds,
-    getImagePreviewDialogLayout,
-    type ImagePreviewViewport,
-} from './imagePreviewSizing';
 
 interface ToolOutputDialogProps {
     popup: ToolPopupContent;
@@ -163,7 +158,7 @@ const usePierreThemeConfig = (): PierreThemeConfig => {
     };
 };
 
-type ViewportSize = ImagePreviewViewport;
+type ViewportSize = { width: number; height: number };
 
 const getWindowViewport = (): ViewportSize => ({
     width: typeof window !== 'undefined' ? window.innerWidth : 0,
@@ -336,11 +331,8 @@ const ImagePreviewDialog: React.FC<{
     }, [popup.image]);
 
     const [currentIndex, setCurrentIndex] = React.useState(0);
-    const [loadedImageSize, setLoadedImageSize] = React.useState<{
-        url: string;
-        width: number;
-        height: number;
-    } | null>(null);
+    const [imageNaturalSize, setImageNaturalSize] = React.useState<{ width: number; height: number } | null>(null);
+    const { isRendered, isVisible, isTransitioning } = usePreviewOverlayState(popup.open);
     const viewport = usePreviewViewport(popup.open);
 
     React.useEffect(() => {
@@ -360,10 +352,9 @@ const ImagePreviewDialog: React.FC<{
         setCurrentIndex(matchingIndex >= 0 ? matchingIndex : 0);
     }, [gallery, popup.image?.index, popup.image?.url, popup.open]);
 
-    const currentImage = gallery[currentIndex] ?? gallery[0];
+    const currentImage = gallery[currentIndex] ?? gallery[0] ?? popup.image;
     const imageTitle = currentImage?.filename || popup.title || 'Image preview';
     const hasMultipleImages = gallery.length > 1;
-    const markdownImage = popup.metadata?.tool === 'markdown-image-preview';
 
     const showPrevious = React.useCallback(() => {
         if (gallery.length <= 1) return;
@@ -381,6 +372,11 @@ const ImagePreviewDialog: React.FC<{
         }
 
         const onKeyDown = (event: KeyboardEvent) => {
+            if (event.key === 'Escape') {
+                onOpenChange(false);
+                return;
+            }
+
             if (event.key === 'ArrowLeft' && hasMultipleImages) {
                 event.preventDefault();
                 showPrevious();
@@ -397,108 +393,126 @@ const ImagePreviewDialog: React.FC<{
         return () => {
             window.removeEventListener('keydown', onKeyDown);
         };
-    }, [hasMultipleImages, popup.open, showNext, showPrevious]);
+    }, [hasMultipleImages, onOpenChange, popup.open, showNext, showPrevious]);
 
-    const imageNaturalSize = loadedImageSize?.url === currentImage?.url
-        ? loadedImageSize
-        : null;
+    React.useEffect(() => {
+        setImageNaturalSize(null);
+    }, [currentImage?.url]);
+
+    const imageDisplaySize = React.useMemo(() => {
+        const maxWidth = Math.max(160, viewport.width * (isMobile ? 0.86 : 0.75));
+        const maxHeight = Math.max(160, viewport.height * (isMobile ? 0.72 : 0.75));
+
+        if (!imageNaturalSize) {
+            return {
+                width: Math.round(maxWidth),
+                height: Math.round(maxHeight),
+            };
+        }
 
-    const { maxWidth, maxHeight } = getImagePreviewBounds(viewport, isMobile, markdownImage);
-    let imageDisplaySize = {
-        width: Math.round(maxWidth),
-        height: Math.round(maxHeight),
-    };
-    if (imageNaturalSize) {
         const widthScale = maxWidth / imageNaturalSize.width;
         const heightScale = maxHeight / imageNaturalSize.height;
         const scale = Math.min(widthScale, heightScale);
-        imageDisplaySize = {
+
+        return {
             width: Math.max(1, Math.round(imageNaturalSize.width * scale)),
             height: Math.max(1, Math.round(imageNaturalSize.height * scale)),
         };
-    }
+    }, [imageNaturalSize, isMobile, viewport.height, viewport.width]);
 
-    const handleImageLoad = React.useCallback((event: React.SyntheticEvent<HTMLImageElement>) => {
-        const element = event.currentTarget;
-        const width = element.naturalWidth;
-        const height = element.naturalHeight;
-        if (width <= 0 || height <= 0) return;
-
-        const url = element.getAttribute('src') ?? '';
-        setLoadedImageSize((previous) => {
-            if (previous && previous.url === url && previous.width === width && previous.height === height) {
-                return previous;
-            }
-            return { url, width, height };
-        });
-    }, []);
-
-    if (!currentImage) {
+    if (!isRendered || !currentImage || typeof document === 'undefined') {
         return null;
     }
 
-    const dialogLayout = getImagePreviewDialogLayout(imageDisplaySize, viewport, isMobile);
-
-    return (
-        <Dialog open={popup.open} onOpenChange={onOpenChange}>
-            <DialogContent
+    const content = (
+        <div className={cn('fixed inset-0 z-50', popup.open ? 'pointer-events-auto' : 'pointer-events-none')}>
+            <div
+                aria-hidden="true"
                 className={cn(
-                    'max-w-none gap-3 overflow-hidden p-4',
-                    '[&>button]:right-3 [&>button]:top-3',
+                    'absolute inset-0 bg-black/40',
+                    isTransitioning && 'transition-opacity duration-150 ease-out',
+                    isVisible ? 'opacity-100' : 'opacity-0'
                 )}
-                style={{
-                    width: `${dialogLayout.dialogWidth}px`,
-                    maxWidth: isMobile ? 'calc(100vw - 1rem)' : 'calc(100vw - 2rem)',
-                    maxHeight: isMobile ? 'calc(100vh - 1rem)' : 'calc(100vh - 2rem)',
-                }}
-                data-openchamber-image-preview-dialog="true"
-                data-openchamber-markdown-image-dialog={markdownImage ? 'true' : undefined}
-                aria-modal="true"
-            >
-                <DialogHeader className="min-w-0 pr-8">
-                    <DialogTitle className="flex min-w-0 items-center gap-2 text-left">
-                        <Icon name="file-image" className="h-4 w-4 shrink-0 text-muted-foreground" />
-                        <span className="min-w-0 truncate" title={imageTitle}>{imageTitle}</span>
-                    </DialogTitle>
-                </DialogHeader>
+                onMouseDown={() => onOpenChange(false)}
+            />
 
+            {hasMultipleImages && (
+                <>
+                    <button
+                        type="button"
+                        onMouseDown={(event) => event.stopPropagation()}
+                        onClick={showPrevious}
+                        className="absolute left-3 top-1/2 -translate-y-1/2 z-10 h-10 w-10 flex items-center justify-center rounded-full bg-black/40 text-foreground/90 hover:bg-black/55 focus:outline-none focus:ring-2 focus:ring-primary/60"
+                        aria-label={t('chat.toolOutputDialog.image.previousAria')}
+                    >
+                        <Icon name="arrow-left-s" className="h-6 w-6" />
+                    </button>
+                    <button
+                        type="button"
+                        onMouseDown={(event) => event.stopPropagation()}
+                        onClick={showNext}
+                        className="absolute right-3 top-1/2 -translate-y-1/2 z-10 h-10 w-10 flex items-center justify-center rounded-full bg-black/40 text-foreground/90 hover:bg-black/55 focus:outline-none focus:ring-2 focus:ring-primary/60"
+                        aria-label={t('chat.toolOutputDialog.image.nextAria')}
+                    >
+                        <Icon name="arrow-right-s" className="h-6 w-6" />
+                    </button>
+                </>
+            )}
+
+            <div
+                className={cn(
+                    'absolute inset-0 flex items-center justify-center pointer-events-none',
+                    isMobile ? 'p-2.5' : 'p-4'
+                )}
+            >
                 <div
-                    className="relative flex min-h-0 max-w-full self-center items-center justify-center overflow-hidden rounded-lg bg-muted/20"
-                    style={{ width: `${dialogLayout.imageWidth}px`, height: `${dialogLayout.imageHeight}px` }}
+                    className={cn(
+                        'pointer-events-auto flex flex-col gap-2',
+                        isTransitioning && 'transition-opacity duration-150 ease-out',
+                        isVisible ? 'opacity-100' : 'opacity-0'
+                    )}
+                    style={{ width: `${imageDisplaySize.width}px` }}
                 >
-                    {hasMultipleImages ? (
-                        <>
-                            <button
-                                type="button"
-                                onClick={showPrevious}
-                                className="absolute left-2 top-1/2 z-10 flex h-10 w-10 -translate-y-1/2 items-center justify-center rounded-full bg-background/85 text-foreground shadow-sm hover:bg-background focus:outline-none focus:ring-2 focus:ring-primary/60"
-                                aria-label={t('chat.toolOutputDialog.image.previousAria')}
-                            >
-                                <Icon name="arrow-left-s" className="h-6 w-6" />
-                            </button>
-                            <button
-                                type="button"
-                                onClick={showNext}
-                                className="absolute right-2 top-1/2 z-10 flex h-10 w-10 -translate-y-1/2 items-center justify-center rounded-full bg-background/85 text-foreground shadow-sm hover:bg-background focus:outline-none focus:ring-2 focus:ring-primary/60"
-                                aria-label={t('chat.toolOutputDialog.image.nextAria')}
-                            >
-                                <Icon name="arrow-right-s" className="h-6 w-6" />
-                            </button>
-                        </>
-                    ) : null}
+                    <div className="flex items-center justify-between gap-2">
+                        <div className="min-w-0 flex-1 text-foreground typography-ui-header font-semibold truncate" title={imageTitle}>
+                            {imageTitle}
+                        </div>
+                        <button
+                            type="button"
+                            className="h-8 w-8 flex items-center justify-center rounded-lg text-muted-foreground/80 hover:text-foreground focus:outline-none focus:ring-2 focus:ring-primary/60"
+                            onClick={() => onOpenChange(false)}
+                            aria-label={t('chat.toolOutputDialog.image.closeAria')}
+                        >
+                            <Icon name="close" className="h-4 w-4" />
+                        </button>
+                    </div>
+
                     <img
                         src={currentImage.url}
                         alt={imageTitle}
-                        className="block h-full w-full object-contain"
+                        className="block object-contain"
+                        style={{ width: `${imageDisplaySize.width}px`, height: `${imageDisplaySize.height}px` }}
                         loading="lazy"
-                        onLoad={handleImageLoad}
-                        data-openchamber-markdown-image-preview={markdownImage ? 'true' : undefined}
+                        onLoad={(event) => {
+                            const element = event.currentTarget;
+                            const width = element.naturalWidth;
+                            const height = element.naturalHeight;
+                            if (width > 0 && height > 0) {
+                                setImageNaturalSize((previous) => {
+                                    if (previous && previous.width === width && previous.height === height) {
+                                        return previous;
+                                    }
+                                    return { width, height };
+                                });
+                            }
+                        }}
                     />
                 </div>
-                <div aria-hidden="true" className="h-4 shrink-0" />
-            </DialogContent>
-        </Dialog>
+            </div>
+        </div>
     );
+
+    return createPortal(content, document.body);
 };
 
 // ── PERF-007: Virtualised sub-components for dialog ──────────────────
diff --git a/packages/ui/src/components/chat/message/imagePreviewSizing.ts b/packages/ui/src/components/chat/message/imagePreviewSizing.ts
deleted file mode 100644
index 9ef842ee..00000000
--- a/packages/ui/src/components/chat/message/imagePreviewSizing.ts
+++ /dev/null
@@ -1,36 +0,0 @@
-export type ImagePreviewViewport = { width: number; height: number };
-type ImagePreviewSize = { width: number; height: number };
-
-export const getImagePreviewBounds = (
-    viewport: ImagePreviewViewport,
-    isMobile: boolean,
-    markdownImage: boolean,
-): { maxWidth: number; maxHeight: number } => ({
-    maxWidth: Math.max(160, viewport.width * (markdownImage ? 0.6 : (isMobile ? 0.86 : 0.75))),
-    maxHeight: Math.max(160, viewport.height * (markdownImage ? 0.8 : (isMobile ? 0.72 : 0.75))),
-});
-
-const IMAGE_DIALOG_MIN_WIDTH = 320;
-const IMAGE_DIALOG_CHROME_WIDTH = 34;
-
-export const getImagePreviewDialogLayout = (
-    image: ImagePreviewSize,
-    viewport: ImagePreviewViewport,
-    isMobile: boolean,
-): { dialogWidth: number; imageWidth: number; imageHeight: number } => {
-    const viewportInset = isMobile ? 16 : 32;
-    const maxDialogWidth = Math.max(160, viewport.width - viewportInset);
-    const minDialogWidth = Math.min(IMAGE_DIALOG_MIN_WIDTH, maxDialogWidth);
-    const dialogWidth = Math.min(
-        maxDialogWidth,
-        Math.max(minDialogWidth, image.width + IMAGE_DIALOG_CHROME_WIDTH),
-    );
-    const availableImageWidth = Math.max(1, dialogWidth - IMAGE_DIALOG_CHROME_WIDTH);
-    const scale = Math.min(1, availableImageWidth / Math.max(1, image.width));
-
-    return {
-        dialogWidth: Math.round(dialogWidth),
-        imageWidth: Math.max(1, Math.round(image.width * scale)),
-        imageHeight: Math.max(1, Math.round(image.height * scale)),
-    };
-};
diff --git a/packages/ui/src/components/chat/message/parts/DOCUMENTATION.md b/packages/ui/src/components/chat/message/parts/DOCUMENTATION.md
index f709d590..d5215518 100644
--- a/packages/ui/src/components/chat/message/parts/DOCUMENTATION.md
+++ b/packages/ui/src/components/chat/message/parts/DOCUMENTATION.md
@@ -63,14 +63,13 @@ Use this doc when you ask an agent to change tool/header/description behavior.
   are limited to 10 MiB, validated as PNG/JPEG/GIF/WebP, and local paths are
   fetched through the active runtime before conversion to data URLs. Local
   Markdown links whose target has one of
-  those image suffixes stay links in the text and open the same standard modal
-  preview as the gallery; image syntax does not insert a large inline image. A
+  those image suffixes stay links in the text and open the same existing
+  full-screen image preview as the gallery; image syntax does not insert a
+  large inline image. A
   completed assistant message hydrates at most 12 unique image candidates,
   including persisted text parts that omit their optional part-level end time.
-  The image modal reserves readable title width even for narrow portrait media.
-  This gallery and modal-preview enhancement is desktop-only. Mobile keeps the
-  standard Markdown rendering path until a dedicated, non-modal full-screen
-  image viewer can own safe areas, orientation, and touch gestures coherently.
+  Gallery clicks do not introduce or alter preview chrome: desktop and mobile
+  both reuse the pre-existing attachment image preview overlay.
 - `read` and `skill` are **static navigation tools** and render via `StaticToolRow`.
 - Every other tool, including search/fetch, OpenCode built-ins, custom tools, plugins, and MCP tools, is **expandable** and renders through `ToolPart`.
 - The managed `openchamber` plugin tool uses the expandable path and hides its broad protocol input. The plugin supplies the selected action's human description as the native tool title; the UI renders that metadata without owning an action map. The full versioned result envelope renders through the same neutral JSON summary/tree/raw views as other tools, without a tool-specific output card.