fix: apply tonal adjustments to photo before letterbox bars are added

Compositing the white letterbox bars before contrastStretch meant the
bars (pure white, often 60%+ of the canvas for an aspect mismatch) were
included in the per-channel histogram. The "lightest 1% to clip to white"
threshold therefore landed inside the bars themselves, raising the
effective white point so the photo's lighter tones got over-clipped to
white and the photo ended up washed out.

Reordering: thumbnail → contrastStretch/modulate/sharpen on the photo
alone → composite onto white canvas → rotate. The contrastStretch's
percentage now uses the photo's actual pixel count too, not the full
canvas, so the 1% clip is honest about how many pixels of real photo
content it's looking at.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/MessageHandler/RenderImageMessageHandler.php

@@ -95,13 +95,34 @@ final class RenderImageMessageHandler
         $imagick->mergeImageLayers(\Imagick::LAYERMETHOD_FLATTEN);
         $imagick->autoOrient();
 
-        // Fit the source into the target box without cropping aggressively;
-        // composite onto a white canvas of exact target dims so an aspect
-        // mismatch (e.g. portrait crop served to a landscape device) shows
-        // up as letterbox bars instead of a brutally center-cropped slice.
-        // For correctly-cropped photos the source already matches the target
-        // aspect and `thumbnailImage` produces target dims with no padding.
+        // Fit the source into the target box without cropping aggressively.
+        // For correctly-cropped photos the source matches the target aspect
+        // and `thumbnailImage` produces target dims with no padding; for an
+        // aspect mismatch the photo comes out smaller than the target and
+        // gets composited onto a white canvas below so it shows up as a
+        // letterbox instead of a brutally center-cropped slice.
         $imagick->thumbnailImage($width, $height, true);
+
+        $imagick->setImageColorspace(\Imagick::COLORSPACE_SRGB);
+
+        // Per-pixel adjustments run on the PHOTO before the white canvas is
+        // composited under it — otherwise the bars dominate the histogram and
+        // the contrast stretch over-clips the photo content to white.
+
+        // Auto-levels: stretch the tonal range, clipping 1% at each end.
+        // Fixes underexposed/dark photos so the full palette range is used.
+        $photoPixels = $imagick->getImageWidth() * $imagick->getImageHeight();
+        $imagick->contrastStretchImage((int) ($photoPixels * 0.01), (int) ($photoPixels * 0.01));
+
+        // Boost saturation 130%.  Dark desaturated photos otherwise map almost
+        // entirely to BLACK with scattered noise dots from error diffusion.
+        $imagick->modulateImage(100, 130, 100);
+
+        // Light sharpen so edges survive the dithering scatter.
+        $imagick->sharpenImage(0, 0.8);
+
+        // Now composite onto a white canvas of exact target dims so that any
+        // aspect mismatch shows up as letterbox bars, not as a sliced crop.
         if ($imagick->getImageWidth() !== $width || $imagick->getImageHeight() !== $height) {
             $canvas = new \Imagick();
             $canvas->newImage($width, $height, new \ImagickPixel('white'));
@@ -123,20 +144,6 @@ final class RenderImageMessageHandler
             $imagick->rotateImage(new \ImagickPixel('white'), -90);
         }
 
-        $imagick->setImageColorspace(\Imagick::COLORSPACE_SRGB);
-
-        // Auto-levels: stretch the tonal range, clipping 1% at each end.
-        // Fixes underexposed/dark photos so the full palette range is used.
-        $pixels = $width * $height;
-        $imagick->contrastStretchImage((int) ($pixels * 0.01), (int) ($pixels * 0.01));
-
-        // Boost saturation 130%.  Dark desaturated photos otherwise map almost
-        // entirely to BLACK with scattered noise dots from error diffusion.
-        $imagick->modulateImage(100, 130, 100);
-
-        // Light sharpen so edges survive the dithering scatter.
-        $imagick->sharpenImage(0, 0.8);
-
         // Build a strip of 6 palette pixels for remapImage
         $palImagick = new \Imagick();
         foreach (self::PALETTE as $rgb) {