fix: keep dashboard shell dimensions stable

surfaces/shell/tests/host-app.test.tsx

@@ -971,6 +971,22 @@ describe("Ekklesia shell — Dashboard navigation", () => {
 });
 
 describe("Ekklesia shell — mount lifecycle", () => {
+  it("keeps fixed shell columns while module content changes width", async () => {
+    await render({ apiBaseUrl, fetch: platformFetch() }, async () =>
+      artifact("example", "0.1.0"),
+    );
+
+    const shell = query("host-shell") as HTMLElement;
+    const aside = shell.querySelector("aside") as HTMLElement;
+    const main = shell.querySelector("main") as HTMLElement;
+    const frame = query("module-container") as HTMLElement;
+    expect(shell.style.gridTemplateColumns).toBe("13rem minmax(0, 1fr)");
+    expect(aside.style.width).toBe("13rem");
+    expect(main.style.minWidth).toBe("0");
+    expect(main.style.overflowX).toBe("auto");
+    expect(frame.style.minWidth).toBe("0");
+  });
+
   it("mounts the first module into the host's own container", async () => {
     const mountedInto: Element[] = [];
     await render({ apiBaseUrl, fetch: platformFetch() }, async () =>