fix(composite): async image decode, skip dead pager, prevent UI freeze

- Decode images in background goroutine, not in Draw()
- Show [loading image...] placeholder until decode completes
- Skip pv.term.Draw() when composite is active (pager got no input)
- Thread-safe access to decoded image cache via sync.Mutex
- Invalidate callback triggers redraw when images finish decoding

app/compositeview.go

@@ -6,6 +6,7 @@ import (
 	"os"
 	"strconv"
 	"strings"
+	"sync"
 
 	"git.sr.ht/~rockorager/vaxis"
 	"git.sr.ht/~rjarry/aerc/lib/log"
@@ -24,30 +25,28 @@ const (
 	blockText  = 0
 	blockImage = 1
 
-	// Default height in terminal rows for an image block.
 	defaultImageHeight = 15
 )
 
 type contentBlock struct {
 	blockType int
-	lines     []string // for text blocks
+	lines     []string
-	imageIdx  int      // for image blocks — index into compositeContent.images
+	imageIdx  int
 }
 
-// compositeContent holds the parsed content model: an ordered sequence of
-// text and image blocks derived from filter output after ExtractImages().
 type compositeContent struct {
 	blocks []contentBlock
 	images []parse.ImageRef
-	width  int // terminal columns available
+	width  int
 
-	// Rendering state (populated lazily during Draw)
+	mu       sync.Mutex
-	decoded  map[int]image.Image  // imageIdx → decoded Go image
+	decoded  map[int]image.Image
-	graphics map[int]vaxis.Image  // imageIdx → Vaxis graphic handle
+	decErrs  map[int]bool // true = decode attempted and failed
+	graphics map[int]vaxis.Image
+
+	invalidate func() // callback to trigger redraw after async decode
 }
 
-// splitContentBlocks splits text at \x00IMG:N\x00 placeholder lines into
-// an ordered slice of text and image blocks.
 func splitContentBlocks(text string, images []parse.ImageRef) []contentBlock {
 	imageSet := make(map[int]bool, len(images))
 	for _, img := range images {
@@ -58,14 +57,12 @@ func splitContentBlocks(text string, images []parse.ImageRef) []contentBlock {
 	var currentLines []string
 
 	lines := strings.Split(text, "\n")
-	// Remove trailing empty line from Split if text ends with \n
 	if len(lines) > 0 && lines[len(lines)-1] == "" {
 		lines = lines[:len(lines)-1]
 	}
 
 	for _, line := range lines {
 		if idx, ok := parsePlaceholder(line); ok && imageSet[idx] {
-			// Flush accumulated text lines
 			if len(currentLines) > 0 {
 				blocks = append(blocks, contentBlock{
 					blockType: blockText,
@@ -90,7 +87,6 @@ func splitContentBlocks(text string, images []parse.ImageRef) []contentBlock {
 	return blocks
 }
 
-// parsePlaceholder checks if a line is \x00IMG:N\x00 and returns N.
 func parsePlaceholder(line string) (int, bool) {
 	if !strings.HasPrefix(line, "\x00IMG:") || !strings.HasSuffix(line, "\x00") {
 		return 0, false
@@ -103,17 +99,52 @@ func parsePlaceholder(line string) (int, bool) {
 	return idx, true
 }
 
-func newCompositeContent(text string, images []parse.ImageRef, width int) *compositeContent {
+func newCompositeContent(text string, images []parse.ImageRef, width int, invalidate func()) *compositeContent {
-	return &compositeContent{
+	cc := &compositeContent{
-		blocks:   splitContentBlocks(text, images),
+		blocks:     splitContentBlocks(text, images),
-		images:   images,
+		images:     images,
-		width:    width,
+		width:      width,
-		decoded:  make(map[int]image.Image),
+		decoded:    make(map[int]image.Image),
-		graphics: make(map[int]vaxis.Image),
+		decErrs:    make(map[int]bool),
+		graphics:   make(map[int]vaxis.Image),
+		invalidate: invalidate,
+	}
+	// Decode all images in background
+	go cc.decodeAllImages()
+	return cc
+}
+
+// decodeAllImages decodes all referenced images in a background goroutine.
+// Calls invalidate() when done so the UI redraws with images.
+func (cc *compositeContent) decodeAllImages() {
+	defer log.PanicHandler()
+	for i, img := range cc.images {
+		f, err := os.Open(img.Path)
+		if err != nil {
+			log.Debugf("composite: open image %d: %v", i, err)
+			cc.mu.Lock()
+			cc.decErrs[i] = true
+			cc.mu.Unlock()
+			continue
+		}
+		decoded, _, err := image.Decode(f)
+		f.Close()
+		if err != nil {
+			log.Debugf("composite: decode image %d: %v", i, err)
+			cc.mu.Lock()
+			cc.decErrs[i] = true
+			cc.mu.Unlock()
+			continue
+		}
+		cc.mu.Lock()
+		cc.decoded[i] = decoded
+		cc.mu.Unlock()
+	}
+	if cc.invalidate != nil {
+		cc.invalidate()
 	}
 }
 
-// totalHeight returns the total height in terminal rows.
 func (cc *compositeContent) totalHeight() int {
 	h := 0
 	for _, b := range cc.blocks {
@@ -127,14 +158,15 @@ func (cc *compositeContent) totalHeight() int {
 	return h
 }
 
-// imageHeight returns the display height for an image block.
 func (cc *compositeContent) imageHeight(idx int) int {
-	if img, ok := cc.decoded[idx]; ok {
+	cc.mu.Lock()
+	img, ok := cc.decoded[idx]
+	cc.mu.Unlock()
+	if ok {
 		bounds := img.Bounds()
 		if bounds.Dx() == 0 {
 			return defaultImageHeight
 		}
-		// Approximate: 2 terminal rows per pixel row (cells are ~2:1 aspect)
 		ratio := float64(bounds.Dy()) / float64(bounds.Dx())
 		h := int(float64(cc.width) * ratio / 2.0)
 		if h < 3 {
@@ -148,49 +180,26 @@ func (cc *compositeContent) imageHeight(idx int) int {
 	return defaultImageHeight
 }
 
-// decodeImage loads and decodes the image file for the given index.
-func (cc *compositeContent) decodeImage(idx int) (image.Image, error) {
-	if img, ok := cc.decoded[idx]; ok {
-		return img, nil
-	}
-	if idx < 0 || idx >= len(cc.images) {
-		return nil, fmt.Errorf("image index %d out of range", idx)
-	}
-	path := cc.images[idx].Path
-	f, err := os.Open(path)
-	if err != nil {
-		return nil, fmt.Errorf("open %s: %w", path, err)
-	}
-	defer f.Close()
-	img, _, err := image.Decode(f)
-	if err != nil {
-		return nil, fmt.Errorf("decode %s: %w", path, err)
-	}
-	cc.decoded[idx] = img
-	return img, nil
-}
-
-// Destroy releases all Vaxis graphics handles.
 func (cc *compositeContent) Destroy() {
+	cc.mu.Lock()
+	defer cc.mu.Unlock()
 	for _, g := range cc.graphics {
 		g.Destroy()
 	}
 	cc.graphics = make(map[int]vaxis.Image)
 }
 
-// CleanupFiles removes temp image files from disk.
 func (cc *compositeContent) CleanupFiles() {
 	for _, img := range cc.images {
 		os.Remove(img.Path)
 	}
 }
 
-// Draw renders the composite content into the given UI context.
+// Draw renders composite content. Only renders images that are already decoded.
-// scroll is the row offset from the top. style is the default text style.
 func (cc *compositeContent) Draw(ctx *ui.Context, scroll int, style ...vaxis.Style) {
 	width := ctx.Width()
 	height := ctx.Height()
-	row := -scroll // start above viewport if scrolled
+	row := -scroll
 
 	defaultStyle := vaxis.Style{}
 	if len(style) > 0 {
@@ -213,25 +222,31 @@ func (cc *compositeContent) Draw(ctx *ui.Context, scroll int, style ...vaxis.Sty
 		case blockImage:
 			imgH := cc.imageHeight(b.imageIdx)
 			if row+imgH > 0 && row < height {
-				cc.drawImage(ctx, b.imageIdx, row, width, imgH)
+				cc.drawImage(ctx, b.imageIdx, row, width, imgH, defaultStyle)
 			}
 			row += imgH
 		}
 	}
 }
 
-func (cc *compositeContent) drawImage(ctx *ui.Context, idx, row, width, height int) {
+func (cc *compositeContent) drawImage(ctx *ui.Context, idx, row, width, height int, style vaxis.Style) {
-	img, err := cc.decodeImage(idx)
+	cc.mu.Lock()
-	if err != nil {
+	img, decoded := cc.decoded[idx]
-		// Show alt text as fallback
+	failed := cc.decErrs[idx]
-		alt := "[image]"
+	cc.mu.Unlock()
-		if idx < len(cc.images) && cc.images[idx].Alt != "" {
+
-			alt = fmt.Sprintf("[%s]", cc.images[idx].Alt)
+	// Show alt text if not yet decoded or failed
+	if !decoded {
+		alt := "[loading image...]"
+		if failed {
+			alt = "[image]"
+			if idx < len(cc.images) && cc.images[idx].Alt != "" {
+				alt = fmt.Sprintf("[%s]", cc.images[idx].Alt)
+			}
 		}
 		if row >= 0 && row < ctx.Height() {
-			ctx.Printf(0, row, vaxis.Style{}, "%s", alt)
+			ctx.Printf(0, row, style, "%s", alt)
 		}
-		log.Debugf("composite: image %d decode error: %v", idx, err)
 		return
 	}
 
@@ -241,16 +256,21 @@ func (cc *compositeContent) drawImage(ctx *ui.Context, idx, row, width, height i
 		var err error
 		graphic, err = vx.NewImage(img)
 		if err != nil {
-			log.Errorf("composite: vaxis image %d error: %v", idx, err)
+			log.Errorf("composite: vaxis NewImage %d: %v", idx, err)
+			if row >= 0 && row < ctx.Height() {
+				alt := "[image: render error]"
+				if idx < len(cc.images) && cc.images[idx].Alt != "" {
+					alt = fmt.Sprintf("[%s]", cc.images[idx].Alt)
+				}
+				ctx.Printf(0, row, style, "%s", alt)
+			}
 			return
 		}
 		cc.graphics[idx] = graphic
 	}
 
-	// Resize to fit
 	graphic.Resize(width, height)
 
-	// Draw within the region — use the sub-window from the current context
 	startRow := row
 	if startRow < 0 {
 		startRow = 0
@@ -259,9 +279,7 @@ func (cc *compositeContent) drawImage(ctx *ui.Context, idx, row, width, height i
 	graphic.Draw(win)
 }
 
-// truncateLine cuts a string to fit width.
 func truncateLine(s string, width int) string {
-	// Use rune count for basic unicode support
 	runes := []rune(s)
 	if len(runes) <= width {
 		return s

app/msgviewer.go

@@ -636,7 +636,8 @@ func (pv *PartViewer) attemptCopy() {
 			if len(images) > 0 {
 				pv.imageRefs = images
 				pv.composite = newCompositeContent(
-					string(cleanedBytes), images, 80)
+					string(cleanedBytes), images, 80,
+					pv.Invalidate)
 				pv.Invalidate()
 			} else {
 				// No images — forward to pager as normal
@@ -835,10 +836,8 @@ func (pv *PartViewer) Draw(ctx *ui.Context) {
 		ctx.Printf(0, 0, style, "%s", pv.err.Error())
 		return
 	}
-	if pv.term != nil {
-		pv.term.Draw(ctx)
-	}
 	// Composite mode: text + inline images from filter output
+	// Skip term.Draw() — pager got no input in composite mode
 	if pv.composite != nil {
 		pv.composite.width = ctx.Width()
 		style := pv.uiConfig.GetStyle(config.STYLE_DEFAULT)
@@ -846,6 +845,9 @@ func (pv *PartViewer) Draw(ctx *ui.Context) {
 		pv.composite.Draw(ctx, pv.scroll, style)
 		return
 	}
+	if pv.term != nil {
+		pv.term.Draw(ctx)
+	}
 	if pv.image != nil && (pv.resized(ctx) || pv.graphic == nil) {
 		// This path should only occur on resizes or the first pass
 		// after the image is downloaded and could be slow due to