chore: establish YCode replication baseline and TODO

scripts/compare-chat-header-pixels.py

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+"""Compare fixed REA captures with the one calibrated YCode header fixture mode."""
+from pathlib import Path
+from hashlib import sha256
+import json
+from PIL import Image, ImageChops
+
+ROOT = Path(__file__).resolve().parents[1]
+OUTPUT = ROOT / '.tmp/chat-header-native-swiftshader-20261016'
+report = json.loads((OUTPUT / 'report.json').read_text(encoding='utf-8'))
+rendering = report['rendering']
+assert rendering['mode'] == 'visible-swiftshader' and rendering['visible']
+assert rendering['gpu']['auxAttributes']['displayType'] == 'ANGLE_SWIFTSHADER'
+assert rendering['gpu']['auxAttributes']['glImplementationParts'] == '(gl=egl-angle,angle=swiftshader)'
+assert rendering['gpuFeatures']['gpu_compositing'] == 'disabled_software'
+regions = [
+    ('title', 'rea-chat-header-final-20261016/workbuddy.png', 'collapsed.png', (308, 50, 388, 74), []),
+    ('search-button', 'rea-chat-header-final-20261016/workbuddy.png', 'collapsed.png', (1215, 46, 1248, 78), []),
+    ('share-button', 'rea-chat-header-final-20261016/workbuddy.png', 'collapsed.png', (1251, 46, 1284, 78), []),
+    ('panel-button', 'rea-chat-header-final-20261016/workbuddy.png', 'collapsed.png', (1287, 46, 1320, 78), []),
+    ('header', 'rea-chat-header-final-20261016/workbuddy.png', 'collapsed.png', (285, 30, 1336, 94), []),
+    # Empty query: no dynamic counter. Exclude only the 3px caret column at the input start.
+    ('search', 'rea-chat-header-title-20261016/workbuddy.png', 'search.png', (947, 46, 1248, 78), [(977, 50, 980, 74)]),
+    ('edit-selected-title', 'rea-chat-header-title-20261016/frame-001.png', 'edit.png', (308, 50, 512, 74), []),
+]
+results = []
+for name, reference, candidate, box, masks in regions:
+    source_path, own_path = ROOT / '.tmp' / reference, OUTPUT / candidate
+    a, b = Image.open(source_path).convert('RGB'), Image.open(own_path).convert('RGB')
+    assert a.size == b.size == (1336, 901)
+    diff = ImageChops.difference(a.crop(box), b.crop(box))
+    compared, changed, total, maximum = 0, 0, 0, 0
+    differences = []
+    for y in range(box[1], box[3]):
+        for x in range(box[0], box[2]):
+            if any(l <= x < r and t <= y < bt for l, t, r, bt in masks):
+                continue
+            delta = diff.getpixel((x - box[0], y - box[1]))
+            compared += 1
+            if any(delta):
+                changed += 1
+                differences.append({'x': x, 'y': y, 'source': a.getpixel((x, y)), 'candidate': b.getpixel((x, y))})
+            total += sum(delta)
+            maximum = max(maximum, *delta)
+    diff.save(OUTPUT / (name + '-diff.png'))
+    results.append({'name': name, 'source': reference, 'candidate': candidate, 'box': box, 'masks': masks,
+        'sourceSha256': sha256(source_path.read_bytes()).hexdigest(), 'candidateSha256': sha256(own_path.read_bytes()).hexdigest(),
+        'comparedPixels': compared, 'differentPixels': changed, 'maxChannelDifference': maximum,
+        'meanAbsoluteChannelDifference': total / (compared * 3), 'differentPixelSamples': differences[:60]})
+summary = {'mode': rendering['mode'], 'displayType': rendering['gpu']['auxAttributes']['displayType'],
+    'gpuCompositing': rendering['gpuFeatures']['gpu_compositing'], 'channelTolerance': 0,
+    'regions': results, 'limitations': ['Fixed Windows/DPR1/1336x901 component fixture only. Production integration, tooltips, prompt-list states, compact/Mac/dark are outside these pixel results.',
+    'Remaining different pixels are preserved and reported; no tolerance or reference-pixel patch was applied.']}
+(OUTPUT / 'pixels.json').write_text(json.dumps(summary, ensure_ascii=False, indent=2), encoding='utf-8')
+print(json.dumps([{'name': r['name'], 'pixels': r['comparedPixels'], 'different': r['differentPixels'], 'max': r['maxChannelDifference']} for r in results]))