Pin kaleido==0.2.1 + native SVG fallback when kaleido fails

src/visualization/plotly_fallback.py

@@ -26,6 +26,19 @@ FONT_FAMILY = (
 )
 
 
+def _fmt(v: float) -> str:
+    """Compact number formatting for axis ticks."""
+    if abs(v) >= 1e9:
+        return f"{v/1e9:.1f}B"
+    if abs(v) >= 1e6:
+        return f"{v/1e6:.1f}M"
+    if abs(v) >= 1e3:
+        return f"{v/1e3:.1f}k"
+    if abs(v - int(v)) < 1e-9:
+        return str(int(v))
+    return f"{v:.2f}"
+
+
 def _theme_layout(title: str = "") -> dict:
     return dict(
         title=dict(text=title, font=dict(family=FONT_FAMILY, size=15, color=INK)),
@@ -139,11 +152,117 @@ class PlotlyRenderer:
         ))
 
     def _to_svg(self, fig: go.Figure) -> str:
+        """Try Plotly→SVG via kaleido; if that fails, hand-draw a simple SVG
+        from the figure's data so the user always gets a visual."""
         try:
             return pio.to_image(fig, format="svg").decode("utf-8")
         except Exception as e:
-            logger.warning(f"to_image SVG failed ({e}); returning HTML")
-            return fig.to_html(include_plotlyjs="cdn", full_html=False)
+            logger.warning(f"Plotly to_image failed ({e}); using native SVG fallback")
+            return self._native_svg(fig)
+
+    def _native_svg(self, fig: go.Figure) -> str:
+        """Hand-draw a simple SVG from the figure data — no kaleido needed."""
+        traces = fig.data
+        if not traces:
+            return self._empty("No data to plot.")
+
+        W, H = 600, 380
+        pad_l, pad_r, pad_t, pad_b = 60, 30, 40, 50
+
+        # Pull the first trace's data
+        t = traces[0]
+        xs = list(getattr(t, "x", []) or [])
+        ys = list(getattr(t, "y", []) or [])
+        # For pies / tables we don't have x/y; fall back to text
+        if not xs or not ys:
+            return self._empty("Unsupported chart shape; see Data section.")
+
+        try:
+            ys_num = [float(y) if y is not None else 0.0 for y in ys]
+        except (TypeError, ValueError):
+            return self._empty("Non-numeric values; see Data section.")
+
+        ymin, ymax = min(ys_num), max(ys_num)
+        if ymin == ymax:
+            ymin -= 1
+            ymax += 1
+        plot_w = W - pad_l - pad_r
+        plot_h = H - pad_t - pad_b
+        n = len(xs)
+
+        def y_to_px(v: float) -> float:
+            return pad_t + plot_h * (1 - (v - ymin) / (ymax - ymin))
+
+        title = (fig.layout.title.text or "").strip() if fig.layout.title else ""
+
+        kind = type(t).__name__.lower()  # "Bar", "Scatter", etc.
+        bars: list[str] = []
+        path: list[str] = []
+
+        if "bar" in kind:
+            bw = max(2.0, plot_w / max(n, 1) * 0.8)
+            for i, v in enumerate(ys_num):
+                cx = pad_l + (i + 0.5) * (plot_w / max(n, 1))
+                top = y_to_px(v)
+                bottom = y_to_px(0)
+                y = min(top, bottom)
+                h = abs(bottom - top)
+                bars.append(
+                    f'<rect x="{cx-bw/2:.1f}" y="{y:.1f}" '
+                    f'width="{bw:.1f}" height="{h:.1f}" '
+                    f'class="chart-accent" rx="2" />'
+                )
+        else:  # treat as line
+            pts = [
+                f"{pad_l + i * (plot_w / max(n - 1, 1)):.1f},{y_to_px(v):.1f}"
+                for i, v in enumerate(ys_num)
+            ]
+            path.append(
+                f'<polyline points="{" ".join(pts)}" fill="none" '
+                f'class="chart-accent" stroke-width="2" />'
+            )
+            for p in pts:
+                x, y = p.split(",")
+                path.append(f'<circle cx="{x}" cy="{y}" r="3" class="chart-accent" />')
+
+        # Axes labels — show min, mid, max on Y
+        y_ticks = []
+        for v in (ymin, (ymin + ymax) / 2, ymax):
+            yp = y_to_px(v)
+            y_ticks.append(
+                f'<line x1="{pad_l}" y1="{yp:.1f}" x2="{W-pad_r}" y2="{yp:.1f}" class="chart-grid" />'
+                f'<text x="{pad_l-8:.1f}" y="{yp+3:.1f}" text-anchor="end" '
+                f'font-size="10" class="chart-muted">{_fmt(v)}</text>'
+            )
+
+        # X labels — every Nth so we don't overlap
+        step = max(1, n // 8)
+        x_labels = []
+        for i in range(0, n, step):
+            cx = pad_l + (i + 0.5) * (plot_w / max(n, 1))
+            label = str(xs[i])
+            if len(label) > 12:
+                label = label[:11] + "…"
+            x_labels.append(
+                f'<text x="{cx:.1f}" y="{H-pad_b+18}" text-anchor="middle" '
+                f'font-size="10" class="chart-muted">{label}</text>'
+            )
+
+        title_el = (
+            f'<text x="{W/2}" y="{20}" text-anchor="middle" '
+            f'font-size="13" font-weight="600" class="chart-ink">{title}</text>'
+            if title else ""
+        )
+
+        return (
+            f'<svg viewBox="0 0 {W} {H}" preserveAspectRatio="xMidYMid meet" '
+            f'style="width:100%;height:auto;display:block">'
+            f'{title_el}'
+            f'{"".join(y_ticks)}'
+            f'{"".join(bars)}{"".join(path)}'
+            f'{"".join(x_labels)}'
+            f'</svg>'
+        )
 
     def _empty(self, msg: str) -> str:
         return f'''<svg viewBox="0 0 600 200" preserveAspectRatio="xMidYMid meet"