feat(web): seed control with -1=random + randomize button

web/src/components/ParamsPanel.tsx

@@ -13,6 +13,39 @@ function renderControl(
 ) {
   const id = `param-${s.name}`;
   const current: unknown = values[s.name] ?? s.default;
+  if (s.name === "seed") {
+    const v = (values[s.name] ?? s.default) as number;
+    return (
+      <div key={s.name} className="space-y-1.5">
+        <label htmlFor={id} className="label-mono">{s.label}</label>
+        <div className="flex items-center gap-3">
+          <input
+            id={id}
+            aria-label={s.label}
+            type="number"
+            min={s.min}
+            step={s.step ?? 1}
+            value={v}
+            onChange={(e) => set(s.name, Number(e.target.value))}
+            className="field-input !w-44 font-mono text-[12px] py-1"
+          />
+          <button
+            type="button"
+            onClick={() => set(s.name, -1)}
+            className="label-mono hover:text-foreground transition-colors"
+          >
+            ↻ random
+          </button>
+          {v === -1 && (
+            <span className="label-mono text-muted-foreground">(random per generate)</span>
+          )}
+        </div>
+        {s.help && (
+          <p className="text-[11px] text-muted-foreground/80 italic">{s.help}</p>
+        )}
+      </div>
+    );
+  }
   if (s.type === "float" || s.type === "int") {
     const n = typeof current === "number" ? current : Number(current);
     return (

web/src/test/ParamsPanel.test.tsx

@@ -58,3 +58,26 @@ describe("ParamsPanel groups", () => {
     expect(onChange).toHaveBeenCalledWith(expect.objectContaining({ top_p: 0.6 }));
   });
 });
+
+describe("ParamsPanel seed control", () => {
+  it("renders an int input plus a randomize button for seed", () => {
+    const specs: ParamSpec[] = [
+      { name: "seed", label: "Seed", type: "int", default: -1, min: -1, step: 1, group: "advanced" },
+    ];
+    render(<ParamsPanel specs={specs} values={{}} onChange={() => {}} />);
+    fireEvent.click(screen.getByText(/advanced/i));
+    expect(screen.getByLabelText(/^seed$/i)).toHaveAttribute("type", "number");
+    expect(screen.getByRole("button", { name: /random/i })).toBeInTheDocument();
+  });
+
+  it("clicking randomize sets seed to -1 via onChange", () => {
+    const specs: ParamSpec[] = [
+      { name: "seed", label: "Seed", type: "int", default: -1, min: -1, step: 1, group: "advanced" },
+    ];
+    const onChange = vi.fn();
+    render(<ParamsPanel specs={specs} values={{ seed: 42 }} onChange={onChange} />);
+    fireEvent.click(screen.getByText(/advanced/i));
+    fireEvent.click(screen.getByRole("button", { name: /random/i }));
+    expect(onChange).toHaveBeenCalledWith(expect.objectContaining({ seed: -1 }));
+  });
+});