feat(highcharts): implement shap-waterfall (#5902)

## Implementation: `shap-waterfall` - python/highcharts

Implements the **python/highcharts** version of `shap-waterfall`.

**File:** `plots/shap-waterfall/implementations/python/highcharts.py`

**Parent Issue:** #5237

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/anyplot/actions/runs/25493326647)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

plots/shap-waterfall/implementations/python/highcharts.py

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+""" anyplot.ai
+shap-waterfall: SHAP Waterfall Plot for Feature Attribution
+Library: highcharts unknown | Python 3.13.13
+Quality: 86/100 | Created: 2026-05-07
+"""
+
+import base64
+import json
+import os
+import tempfile
+import time
+import urllib.request
+from pathlib import Path
+
+from selenium import webdriver
+from selenium.webdriver.chrome.options import Options
+
+
+# Theme tokens
+THEME = os.getenv("ANYPLOT_THEME", "light")
+PAGE_BG = "#FAF8F1" if THEME == "light" else "#1A1A17"
+INK = "#1A1A17" if THEME == "light" else "#F0EFE8"
+INK_SOFT = "#4A4A44" if THEME == "light" else "#B8B7B0"
+GRID = "rgba(26,26,23,0.10)" if THEME == "light" else "rgba(240,239,232,0.10)"
+
+BRAND = "#009E73"  # Okabe-Ito pos 1 — baseline & prediction bars
+POSITIVE_COLOR = "#D55E00"  # Okabe-Ito pos 2 — positive SHAP (pushes risk up)
+NEGATIVE_COLOR = "#0072B2"  # Okabe-Ito pos 3 — negative SHAP (pushes risk down)
+
+# Data — credit scoring model explaining a single loan application
+# Features sorted by absolute SHAP value (largest contribution first = top of chart)
+BASE_VALUE = 0.35  # Expected probability of default across all applicants
+
+features = [
+    "Credit Score",
+    "Debt-to-Income",
+    "Annual Income",
+    "Loan Amount",
+    "Employment Years",
+    "Payment History",
+    "Open Accounts",
+    "Credit Inquiries",
+    "Credit Age",
+    "Savings Balance",
+]
+shap_values = [-0.18, +0.15, -0.12, +0.09, -0.07, -0.05, +0.04, +0.03, -0.02, -0.02]
+FINAL_VALUE = round(BASE_VALUE + sum(shap_values), 4)
+
+# Build waterfall data: base bar → feature deltas → isSum final
+categories = ["E[f(x)] Baseline", *features, "f(x) Prediction"]
+
+data_points = [{"y": BASE_VALUE, "color": BRAND}]
+for sv in shap_values:
+    data_points.append({"y": sv, "color": POSITIVE_COLOR if sv > 0 else NEGATIVE_COLOR})
+data_points.append({"isSum": True, "color": BRAND})
+
+# Chart configuration (JSON-serializable; JS functions injected via string replace)
+chart_config = {
+    "chart": {
+        "type": "waterfall",
+        "inverted": True,
+        "width": 4800,
+        "height": 2700,
+        "backgroundColor": PAGE_BG,
+        "marginLeft": 340,
+        "marginRight": 220,
+        "marginTop": 130,
+        "marginBottom": 220,
+        "style": {"fontFamily": "Arial, sans-serif", "color": INK},
+    },
+    "title": {
+        "text": "Credit Default Risk · shap-waterfall · highcharts · anyplot.ai",
+        "style": {"fontSize": "28px", "fontWeight": "normal", "color": INK},
+        "align": "left",
+        "x": 340,
+    },
+    "xAxis": {
+        "categories": categories,
+        "title": {"text": "Feature", "style": {"fontSize": "22px", "color": INK}},
+        "labels": {"style": {"fontSize": "20px", "color": INK_SOFT}},
+        "lineColor": INK_SOFT,
+        "tickColor": INK_SOFT,
+        "gridLineColor": GRID,
+    },
+    "yAxis": {
+        "title": {"text": "Probability of Default", "style": {"fontSize": "22px", "color": INK}},
+        "labels": {"style": {"fontSize": "18px", "color": INK_SOFT}, "formatter": "__YAXIS_FORMATTER__"},
+        "lineColor": INK_SOFT,
+        "tickColor": INK_SOFT,
+        "gridLineColor": GRID,
+        "gridLineWidth": 1,
+        "min": -0.02,
+        "max": 0.50,
+        "plotLines": [
+            {
+                "value": BASE_VALUE,
+                "color": INK_SOFT,
+                "width": 2,
+                "dashStyle": "Dash",
+                "zIndex": 2,
+                "label": {
+                    "text": f"Baseline {BASE_VALUE:.2f}",
+                    "align": "right",
+                    "rotation": 0,
+                    "x": -6,
+                    "y": -12,
+                    "style": {"fontSize": "16px", "color": INK_SOFT},
+                },
+            },
+            {
+                "value": FINAL_VALUE,
+                "color": BRAND,
+                "width": 2,
+                "dashStyle": "ShortDot",
+                "zIndex": 2,
+                "label": {
+                    "text": f"Prediction {FINAL_VALUE:.2f}",
+                    "align": "right",
+                    "rotation": 0,
+                    "x": -6,
+                    "y": -12,
+                    "style": {"fontSize": "16px", "color": BRAND},
+                },
+            },
+        ],
+    },
+    "legend": {"enabled": False},
+    "tooltip": {"enabled": False},
+    "plotOptions": {
+        "waterfall": {
+            "lineWidth": 2,
+            "lineColor": INK_SOFT,
+            "borderWidth": 0,
+            "groupPadding": 0.05,
+            "pointPadding": 0.08,
+            "dataLabels": {
+                "enabled": True,
+                "formatter": "__DATA_LABEL_FORMATTER__",
+                "style": {"fontSize": "18px", "fontWeight": "bold", "color": INK, "textOutline": "none"},
+                "inside": False,
+            },
+        }
+    },
+    "series": [{"name": "SHAP Attribution", "data": data_points}],
+}
+
+# Inject JavaScript formatter functions (not JSON-serializable, so replace placeholders)
+config_json = json.dumps(chart_config)
+
+yaxis_formatter = """function() {
+    return Highcharts.numberFormat(this.value, 2);
+}"""
+config_json = config_json.replace('"__YAXIS_FORMATTER__"', yaxis_formatter)
+
+data_label_formatter = """function() {
+    if (this.point.isSum) {
+        return 'f(x) = ' + Highcharts.numberFormat(this.y, 2);
+    }
+    if (this.point.index === 0) {
+        return 'E[f(x)] = ' + Highcharts.numberFormat(this.y, 2);
+    }
+    var sign = this.y > 0 ? '+' : '';
+    return sign + Highcharts.numberFormat(this.y, 3);
+}"""
+config_json = config_json.replace('"__DATA_LABEL_FORMATTER__"', data_label_formatter)
+
+
+# Download Highcharts JS with multiple CDN fallbacks
+def download_js(paths, timeout=15):
+    cdn_bases = [
+        "https://cdn.jsdelivr.net/npm/highcharts@11/",
+        "https://unpkg.com/highcharts@11/",
+        "https://code.highcharts.com/",
+    ]
+    for path in paths:
+        for base in cdn_bases:
+            url = base + path
+            for attempt in range(2):
+                try:
+                    req = urllib.request.Request(url, headers={"User-Agent": "Mozilla/5.0"})
+                    with urllib.request.urlopen(req, timeout=timeout) as resp:
+                        return resp.read().decode("utf-8")
+                except Exception:
+                    if attempt == 0:
+                        time.sleep(1)
+    return None
+
+
+highcharts_js = download_js(["highcharts.js"])
+if highcharts_js is None:
+    raise RuntimeError("Failed to download highcharts.js from all CDNs")
+
+# Waterfall chart type lives in highcharts-more.js
+highcharts_more_js = download_js(["highcharts-more.js"])
+if highcharts_more_js is None:
+    raise RuntimeError("Failed to download highcharts-more.js from all CDNs")
+
+# Generate HTML with inline Highcharts JS (core + more module for waterfall type)
+html_content = f"""<!DOCTYPE html>
+<html>
+<head>
+    <meta charset="utf-8">
+    <script>{highcharts_js}</script>
+    <script>{highcharts_more_js}</script>
+</head>
+<body style="margin:0; background:{PAGE_BG};">
+    <div id="container" style="width: 4800px; height: 2700px;"></div>
+    <script>
+        Highcharts.chart('container', {config_json});
+    </script>
+</body>
+</html>"""
+
+# Save interactive HTML artifact
+with open(f"plot-{THEME}.html", "w", encoding="utf-8") as f:
+    f.write(html_content)
+
+# Screenshot via headless Chrome with CDP for full-resolution capture
+with tempfile.NamedTemporaryFile(mode="w", suffix=".html", delete=False, encoding="utf-8") as f:
+    f.write(html_content)
+    temp_path = f.name
+
+chrome_options = Options()
+chrome_options.add_argument("--headless=new")
+chrome_options.add_argument("--no-sandbox")
+chrome_options.add_argument("--disable-dev-shm-usage")
+chrome_options.add_argument("--disable-gpu")
+chrome_options.add_argument("--hide-scrollbars")
+chrome_options.add_argument("--force-device-scale-factor=1")
+
+driver = webdriver.Chrome(options=chrome_options)
+driver.get(f"file://{temp_path}")
+time.sleep(5)
+
+screenshot_config = {"captureBeyondViewport": True, "clip": {"x": 0, "y": 0, "width": 4800, "height": 2700, "scale": 1}}
+result = driver.execute_cdp_cmd("Page.captureScreenshot", screenshot_config)
+with open(f"plot-{THEME}.png", "wb") as f:
+    f.write(base64.b64decode(result["data"]))
+driver.quit()
+
+Path(temp_path).unlink()