fix(settings): keep staged object settings stable across renders (#293)

Settings › HTTP Proxy crashed ("Maximum update depth exceeded") when switching to No proxy or Manual. useSetting selected stagedValue() inside the zustand selector; for an object key ("proxy") whose child keys are staged separately ("proxy.mode", "proxy.host"), stagedValue builds a new merged object on every call, so the snapshot was never stable. useSetting now reuses useStagedValue, which selects base and staged separately and memoises the merge — covering every useSetting on an object-valued key. No other selector calls stagedValue.

Fixes #285

src/features/settings/__tests__/dialog.test.tsx

@@ -24,8 +24,9 @@ import { registerAction, executeAction } from "@/platform/actions";
 import { useProject } from "@/platform/project";
 import { useKeymap } from "@/platform/keymap";
 import { ContextMenuHost } from "@/ui";
+import { PageContext, useSetting } from "../components/context";
 import { DEFAULT_SETTINGS, setAt } from "../model/schema";
-import { stage, useSettingsDialog } from "../model/staging";
+import { openSettings, stage, useSettingsDialog } from "../model/staging";
 import { SettingsDialog } from "../dialog/SettingsDialog";
 import { activate } from "..";
 import { MessagesHost } from "@/workbench/messages";
@@ -271,6 +272,37 @@ describe("Settings dialog", () => {
     });
   });
 
+  it("keeps object settings stable when child keys are staged (HTTP Proxy)", async () => {
+    const seen: Array<{ mode: string; host: string }> = [];
+    function Probe() {
+      const [proxy] = useSetting<{ mode: string; host: string }>("proxy", "global");
+      seen.push(proxy);
+      return <output data-testid="proxy">{`${proxy.mode}:${proxy.host}`}</output>;
+    }
+    openSettings("general.httpProxy");
+    const view = render(
+      <PageContext.Provider value={{ pageId: "general.httpProxy", scope: "global" }}>
+        <Probe />
+      </PageContext.Provider>,
+    );
+    expect(screen.getByTestId("proxy")).toHaveTextContent("auto:");
+    act(() => {
+      stage("general.httpProxy", "global", "proxy.mode", "manual");
+      stage("general.httpProxy", "global", "proxy.host", "127.0.0.1");
+    });
+    expect(screen.getByTestId("proxy")).toHaveTextContent("manual:127.0.0.1");
+    expect(seen.at(-1)).toMatchObject({ mode: "manual", host: "127.0.0.1" });
+    view.unmount();
+
+    const dialog = await openDialog("general.httpProxy");
+    fireEvent.click(within(dialog).getByRole("radio", { name: "Manual proxy configuration" }));
+    expect(within(dialog).getByRole("radio", { name: "Manual proxy configuration" })).toBeChecked();
+    fireEvent.change(within(dialog).getByLabelText("Host name"), { target: { value: "127.0.0.1" } });
+    expect(within(dialog).getByLabelText("Host name")).toHaveValue("127.0.0.1");
+    fireEvent.click(within(dialog).getByRole("radio", { name: "No proxy" }));
+    expect(within(dialog).getByRole("radio", { name: "No proxy" })).toBeChecked();
+  });
+
   it("survives invalid settings values", async () => {
     act(() =>
       useProject.setState({

src/features/settings/components/context.ts

@@ -19,7 +19,7 @@ export function usePageContext(): PageContextValue {
 export function useSetting<T>(key: string, scopeOverride?: Scope): [T, (value: T) => void] {
   const { pageId, scope: pageScope } = usePageContext();
   const scope = scopeOverride ?? pageScope;
-  const value = useSettingsDialog((s) => stagedValue(s, scope, key)) as T;
+  const value = useStagedValue(scope, key) as T;
   const set = useCallback((v: T) => stage(pageId, scope, key, v), [pageId, scope, key]);
   return [value, set];
 }