diff --git a/effect/phasevortex/README.md b/effect/phasevortex/README.md
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+# Phase Vortex Brush
+
+Phase Vortex is a stroke-following interference brush for Quantum Brush. It treats the user's stroke as a phase object inside a balanced Mach-Zehnder interferometer: every affected pixel receives a relative phase, and the output intensity follows the single-photon interference probability `P = (1 + V cos(phi)) / 2`.
+
+The result is a set of coherent color and brightness fringes that bend around the stroke. The `Winding` control adds an orbital-angular-momentum-like phase term, turning straight fringes into vortex patterns around the clicked or drawn region.
+
+## Parameters
+
+- `Radius`: width of the affected region around the stroke.
+- `Fringe Spacing`: distance between interference bands.
+- `Winding`: angular phase circulation; positive and negative values swirl in opposite directions.
+- `Strength`: how strongly the computed interference pattern is blended into the image.
+- `Hue Shift`: how much the bright and dark ports push hue in opposite directions.
+- `Coherence`: fringe visibility. Lower values mimic decoherence by flattening the pattern.
+
+## Quantum Background
+
+A balanced Mach-Zehnder interferometer splits a quantum amplitude into two paths and recombines it. A relative phase `phi` between the paths changes the probability of detecting the particle at either output port. This brush maps path distance, stroke direction, and angular winding into that phase, then uses the resulting probability field as a visual transformation.
+
+High coherence gives sharp interference fringes. Low coherence washes them out, similar to losing phase information through environmental noise.
+
+## Creative Use
+
+Phase Vortex works well on long curved strokes, spirals, and circular gestures. It can create water-like caustics, energy halos, or orbital ripples while preserving the original image texture underneath. For subtle effects, lower `Strength` and `Hue Shift`; for a visible quantum-poster look, increase `Winding` and `Coherence`.
+
+## Files
+
+- `phasevortex.py`: brush implementation.
+- `phasevortex_requirements.json`: Quantum Brush parameter metadata.
+- `docs/before.png` and `docs/after.png`: generated example images.
diff --git a/effect/phasevortex/__init__.py b/effect/phasevortex/__init__.py
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+
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diff --git a/effect/phasevortex/phasevortex.py b/effect/phasevortex/phasevortex.py
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+import colorsys
+import numpy as np
+
+
+def _safe_path(path):
+    path = np.asarray(path, dtype=float)
+    if path.ndim != 2 or path.shape[1] != 2:
+        return np.empty((0, 2), dtype=float)
+    return path
+
+
+def _rgb_to_hls(rgb):
+    flat = rgb.reshape(-1, 3)
+    converted = [colorsys.rgb_to_hls(float(r), float(g), float(b)) for r, g, b in flat]
+    return np.asarray(converted, dtype=float).reshape(rgb.shape)
+
+
+def _hls_to_rgb(hls):
+    flat = hls.reshape(-1, 3)
+    converted = [colorsys.hls_to_rgb(float(h), float(l), float(s)) for h, l, s in flat]
+    return np.asarray(converted, dtype=float).reshape(hls.shape)
+
+
+def _points_within_radius(points, radius, border):
+    points = np.asarray(points, dtype=int)
+    if len(points) == 0:
+        return np.empty((0, 2), dtype=int)
+
+    min_yx = np.maximum(points.min(axis=0) - radius - 1, [0, 0])
+    max_yx = np.minimum(points.max(axis=0) + radius + 1, [border[0] - 1, border[1] - 1])
+    yy, xx = np.mgrid[min_yx[0]:max_yx[0] + 1, min_yx[1]:max_yx[1] + 1]
+    grid = np.stack([yy.ravel(), xx.ravel()], axis=1)
+
+    mask = np.zeros(len(grid), dtype=bool)
+    batch = 2048
+    radius_sq = radius * radius
+    for start in range(0, len(grid), batch):
+        stop = start + batch
+        delta = grid[start:stop, None, :] - points[None, :, :]
+        mask[start:stop] = np.min(np.sum(delta * delta, axis=2), axis=1) <= radius_sq
+    return grid[mask]
+
+
+def _anchor_points(path, clicks):
+    clicks = np.asarray(clicks, dtype=float)
+    if clicks.ndim == 2 and clicks.shape[1] == 2 and len(clicks) > 0:
+        return clicks
+    if len(path) == 0:
+        return np.empty((0, 2), dtype=float)
+    return np.array([path[0], path[len(path) // 2], path[-1]], dtype=float)
+
+
+def _nearest_path_distance(region, path, max_points=500):
+    if len(path) == 0:
+        return np.zeros(len(region), dtype=float)
+
+    if len(path) > max_points:
+        sample_idx = np.linspace(0, len(path) - 1, max_points).astype(int)
+        path = path[sample_idx]
+
+    # Batched squared distances keep the brush responsive on large strokes.
+    distances = np.empty(len(region), dtype=float)
+    batch = 2048
+    for start in range(0, len(region), batch):
+        stop = start + batch
+        delta = region[start:stop, None, :] - path[None, :, :]
+        distances[start:stop] = np.sqrt(np.min(np.sum(delta * delta, axis=2), axis=1))
+    return distances
+
+
+def _mach_zehnder_probability(phase, coherence):
+    # A single photon entering a balanced Mach-Zehnder interferometer exits one
+    # port with P = (1 + V cos(phi)) / 2. Coherence acts as fringe visibility.
+    return 0.5 + 0.5 * np.clip(coherence, 0.0, 1.0) * np.cos(phase)
+
+
+def _phase_field(region, path, anchors, radius, fringe_spacing, winding):
+    center = anchors.mean(axis=0) if len(anchors) else path[len(path) // 2]
+    rel = region.astype(float) - center
+    angle = np.arctan2(rel[:, 0], rel[:, 1])
+    radial = np.sqrt(np.sum(rel * rel, axis=1))
+    path_dist = _nearest_path_distance(region, path)
+
+    stroke_axis = path[-1] - path[0] if len(path) > 1 else np.array([1.0, 0.0])
+    norm = np.linalg.norm(stroke_axis)
+    if norm < 1e-6:
+        stroke_axis = np.array([1.0, 0.0])
+        norm = 1.0
+    stroke_axis = stroke_axis / norm
+    momentum = (region.astype(float) - center) @ stroke_axis / max(fringe_spacing, 1e-6)
+
+    vortex = winding * angle
+    ripples = 2 * np.pi * (path_dist / max(fringe_spacing, 1e-6))
+    envelope = np.clip(1.0 - path_dist / max(radius, 1), 0.0, 1.0)
+    radial_chirp = 0.35 * np.sqrt(radial / max(radius, 1))
+    phase = ripples + vortex + momentum + radial_chirp
+    return phase, envelope
+
+
+def run(params):
+    image = params["stroke_input"]["image_rgba"].copy()
+    assert image.shape[-1] == 4, "Image must be RGBA format"
+
+    path = _safe_path(params["stroke_input"].get("path", []))
+    if len(path) == 0:
+        return image
+
+    radius = int(params["user_input"]["Radius"])
+    fringe_spacing = float(params["user_input"]["Fringe Spacing"])
+    winding = float(params["user_input"]["Winding"])
+    strength = float(params["user_input"]["Strength"])
+    hue_shift = float(params["user_input"]["Hue Shift"])
+    coherence = float(params["user_input"]["Coherence"])
+
+    height, width = image.shape[:2]
+    region = _points_within_radius(path.astype(int), radius, border=(height, width))
+    if len(region) == 0:
+        return image
+
+    # Clipping at the border can duplicate coordinates, so keep each pixel once.
+    region = np.unique(region, axis=0)
+    anchors = _anchor_points(path, params["stroke_input"].get("clicks", []))
+    phase, envelope = _phase_field(region, path, anchors, radius, fringe_spacing, winding)
+    probability = _mach_zehnder_probability(phase, coherence)
+
+    selection = image[region[:, 0], region[:, 1]].astype(np.float32) / 255.0
+    hls = _rgb_to_hls(selection[..., :3])
+
+    signed_fringe = (probability - 0.5) * 2.0
+    local_strength = strength * envelope
+    hls[..., 0] = (hls[..., 0] + hue_shift * signed_fringe * local_strength) % 1.0
+    hls[..., 1] = np.clip(
+        hls[..., 1] + 0.28 * signed_fringe * local_strength,
+        0.0,
+        1.0,
+    )
+    hls[..., 2] = np.clip(
+        hls[..., 2] * (1.0 + 0.22 * local_strength * np.abs(signed_fringe)),
+        0.0,
+        1.0,
+    )
+
+    rgb = (_hls_to_rgb(hls) * 255).astype(np.uint8)
+    alpha = selection[..., 3:4]
+    blended_rgb = (
+        selection[..., :3] * (1.0 - local_strength[:, None] * alpha)
+        + (rgb.astype(np.float32) / 255.0) * (local_strength[:, None] * alpha)
+    )
+    image[region[:, 0], region[:, 1], :3] = np.clip(blended_rgb * 255, 0, 255).astype(np.uint8)
+    image[region[:, 0], region[:, 1], 3] = np.maximum(
+        image[region[:, 0], region[:, 1], 3],
+        (255 * np.clip(local_strength, 0.0, 1.0)).astype(np.uint8),
+    )
+    return image
diff --git a/effect/phasevortex/phasevortex_requirements.json b/effect/phasevortex/phasevortex_requirements.json
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+{
+  "name": "Phase Vortex",
+  "id": "phasevortex",
+  "author": "qdwg with OpenAI Codex",
+  "version": "1.0.0",
+  "description": "A Mach-Zehnder-style interference brush that turns stroke geometry into color phase ripples and vortex-like brightness fringes.",
+  "dependencies": {
+    "numpy": ">=2.1.0"
+  },
+  "user_input": {
+    "Radius": {
+      "type": "int",
+      "min": 4,
+      "max": 120,
+      "default": 36
+    },
+    "Fringe Spacing": {
+      "type": "float",
+      "min": 4.0,
+      "max": 80.0,
+      "default": 18.0
+    },
+    "Winding": {
+      "type": "float",
+      "min": -6.0,
+      "max": 6.0,
+      "default": 1.5
+    },
+    "Strength": {
+      "type": "float",
+      "min": 0.0,
+      "max": 1.0,
+      "default": 0.65
+    },
+    "Hue Shift": {
+      "type": "float",
+      "min": -1.0,
+      "max": 1.0,
+      "default": 0.18
+    },
+    "Coherence": {
+      "type": "float",
+      "min": 0.0,
+      "max": 1.0,
+      "default": 0.85
+    }
+  },
+  "stroke_input": {
+    "image_rgba": "array",
+    "path": "array",
+    "clicks": "array"
+  },
+  "flags": {
+    "smooth_path": true
+  }
+}