diff --git a/ui/src/styles/components.css b/ui/src/styles/components.css
index bc598c1b633..d42e8cdfa1b 100644
--- a/ui/src/styles/components.css
+++ b/ui/src/styles/components.css
@@ -4848,14 +4848,29 @@ td.data-table-key-col {
   position: fixed;
   inset: 0;
   z-index: 1000;
+  width: 100vw;
+  max-width: none;
+  height: 100dvh;
+  max-height: none;
+  margin: 0;
+  border: 0;
+  box-sizing: border-box;
   display: flex;
   align-items: flex-start;
   justify-content: center;
   padding-top: min(20vh, 160px);
+  padding-right: 0;
+  padding-bottom: 0;
+  padding-left: 0;
   background: rgba(0, 0, 0, 0.5);
+  color: var(--text);
   animation: fade-in 0.12s ease-out;
 }
 
+.cmd-palette-overlay::backdrop {
+  background: transparent;
+}
+
 .cmd-palette {
   width: min(560px, 90vw);
   overflow: hidden;
@@ -4866,6 +4881,19 @@ td.data-table-key-col {
   animation: scale-in 0.15s ease-out;
 }
 
+.cmd-palette__label {
+  position: absolute;
+  width: 1px;
+  height: 1px;
+  margin: -1px;
+  padding: 0;
+  border: 0;
+  overflow: hidden;
+  clip: rect(0 0 0 0);
+  clip-path: inset(50%);
+  white-space: nowrap;
+}
+
 .cmd-palette__input {
   width: 100%;
   padding: 14px 18px;
diff --git a/ui/src/ui/views/command-palette.test.ts b/ui/src/ui/views/command-palette.test.ts
index b6a888cd67d..b010ac5f54e 100644
--- a/ui/src/ui/views/command-palette.test.ts
+++ b/ui/src/ui/views/command-palette.test.ts
@@ -1,9 +1,76 @@
-import { afterEach, describe, expect, it } from "vitest";
+import { nothing, render } from "lit";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import { i18n } from "../../i18n/index.ts";
 import { refreshSlashCommands, resetSlashCommandsForTest } from "../chat/slash-commands.ts";
-import { getFilteredPaletteItems, getPaletteItems } from "./command-palette.ts";
+import {
+  getFilteredPaletteItems,
+  getPaletteItems,
+  renderCommandPalette,
+  type CommandPaletteProps,
+} from "./command-palette.ts";
+
+let container: HTMLDivElement;
+
+const showModalDescriptor = Object.getOwnPropertyDescriptor(
+  HTMLDialogElement.prototype,
+  "showModal",
+);
+
+function nextFrame() {
+  return new Promise<void>((resolve) => {
+    requestAnimationFrame(() => resolve());
+  });
+}
+
+function installDialogPolyfill() {
+  Object.defineProperty(HTMLDialogElement.prototype, "showModal", {
+    configurable: true,
+    value(this: HTMLDialogElement) {
+      this.setAttribute("open", "");
+    },
+  });
+}
+
+function restoreShowModalDescriptor() {
+  if (showModalDescriptor) {
+    Object.defineProperty(HTMLDialogElement.prototype, "showModal", showModalDescriptor);
+    return;
+  }
+  delete (HTMLDialogElement.prototype as Partial<HTMLDialogElement>).showModal;
+}
+
+function createProps(overrides: Partial<CommandPaletteProps> = {}): CommandPaletteProps {
+  return {
+    open: true,
+    query: "",
+    activeIndex: 0,
+    onToggle: () => undefined,
+    onQueryChange: () => undefined,
+    onActiveIndexChange: () => undefined,
+    onNavigate: () => undefined,
+    onSlashCommand: () => undefined,
+    ...overrides,
+  };
+}
+
+async function renderPalette(overrides: Partial<CommandPaletteProps> = {}) {
+  const props = createProps(overrides);
+  render(renderCommandPalette(props), container);
+  await nextFrame();
+  return props;
+}
+
+beforeEach(() => {
+  installDialogPolyfill();
+  container = document.createElement("div");
+  document.body.append(container);
+});
 
 afterEach(async () => {
+  render(nothing, container);
+  container.remove();
+  restoreShowModalDescriptor();
+  vi.restoreAllMocks();
   resetSlashCommandsForTest();
   await i18n.setLocale("en");
 });
@@ -69,4 +136,90 @@ describe("command palette", () => {
       }),
     );
   });
+
+  it("renders a labelled modal combobox with listbox options", async () => {
+    await renderPalette({ query: "overview", activeIndex: 0 });
+
+    const dialog = container.querySelector<HTMLDialogElement>("dialog.cmd-palette-overlay");
+    expect(dialog).not.toBeNull();
+    expect(dialog!.open).toBe(true);
+    expect(dialog!.hasAttribute("role")).toBe(false);
+    expect(dialog!.hasAttribute("aria-modal")).toBe(false);
+    expect(dialog!.getAttribute("aria-labelledby")).toBe("cmd-palette-label");
+
+    const label = container.querySelector<HTMLLabelElement>("#cmd-palette-label");
+    const input = container.querySelector<HTMLInputElement>("#cmd-palette-input");
+    const listbox = container.querySelector<HTMLElement>("#cmd-palette-listbox");
+    expect(label?.textContent).toBe("Type a command…");
+    expect(label?.getAttribute("for")).toBe("cmd-palette-input");
+    expect(input).not.toBeNull();
+    expect(input!.getAttribute("role")).toBe("combobox");
+    expect(input!.getAttribute("aria-autocomplete")).toBe("list");
+    expect(input!.getAttribute("aria-expanded")).toBe("true");
+    expect(input!.getAttribute("aria-controls")).toBe("cmd-palette-listbox");
+    expect(input!.getAttribute("aria-activedescendant")).toBe("cmd-palette-option-nav-overview");
+    expect(document.activeElement).toBe(input);
+
+    expect(listbox).not.toBeNull();
+    expect(listbox!.getAttribute("role")).toBe("listbox");
+    const option = listbox!.querySelector<HTMLElement>("#cmd-palette-option-nav-overview");
+    expect(option).not.toBeNull();
+    expect(option!.getAttribute("role")).toBe("option");
+    expect(option!.getAttribute("aria-selected")).toBe("true");
+  });
+
+  it("traps Tab on the combobox and restores focus on Escape", async () => {
+    const returnTarget = document.createElement("button");
+    returnTarget.textContent = "Open palette";
+    document.body.append(returnTarget);
+    returnTarget.focus();
+    const onToggle = vi.fn();
+
+    await renderPalette({ onToggle });
+    const input = container.querySelector<HTMLInputElement>("#cmd-palette-input");
+    expect(input).not.toBeNull();
+    expect(document.activeElement).toBe(input);
+
+    const tab = new KeyboardEvent("keydown", {
+      key: "Tab",
+      bubbles: true,
+      cancelable: true,
+    });
+    input!.dispatchEvent(tab);
+    expect(tab.defaultPrevented).toBe(true);
+    expect(document.activeElement).toBe(input);
+
+    const escape = new KeyboardEvent("keydown", {
+      key: "Escape",
+      bubbles: true,
+      cancelable: true,
+    });
+    input!.dispatchEvent(escape);
+    expect(escape.defaultPrevented).toBe(true);
+    expect(onToggle).toHaveBeenCalledTimes(1);
+
+    await nextFrame();
+    expect(document.activeElement).toBe(returnTarget);
+    returnTarget.remove();
+  });
+
+  it("does not toggle twice when Escape is followed by dialog cancel", async () => {
+    const onToggle = vi.fn();
+    await renderPalette({ onToggle });
+    const dialog = container.querySelector<HTMLDialogElement>("dialog.cmd-palette-overlay");
+    const input = container.querySelector<HTMLInputElement>("#cmd-palette-input");
+    expect(dialog).not.toBeNull();
+    expect(input).not.toBeNull();
+
+    input!.dispatchEvent(
+      new KeyboardEvent("keydown", {
+        key: "Escape",
+        bubbles: true,
+        cancelable: true,
+      }),
+    );
+    dialog!.dispatchEvent(new Event("cancel", { cancelable: true }));
+
+    expect(onToggle).toHaveBeenCalledTimes(1);
+  });
 });
diff --git a/ui/src/ui/views/command-palette.ts b/ui/src/ui/views/command-palette.ts
index 28a6d219d8c..af073f481f0 100644
--- a/ui/src/ui/views/command-palette.ts
+++ b/ui/src/ui/views/command-palette.ts
@@ -135,16 +135,40 @@ function groupItems(items: PaletteItem[]): Array<[string, PaletteItem[]]> {
 }
 
 let previouslyFocused: Element | null = null;
+let activeDialog: HTMLDialogElement | null = null;
+
+const FOCUSABLE_SELECTOR = [
+  "a[href]",
+  "button:not([disabled])",
+  "input:not([disabled])",
+  "select:not([disabled])",
+  "textarea:not([disabled])",
+  "summary",
+  "[tabindex]:not([tabindex='-1'])",
+].join(",");
+
+const paletteDialogLabelId = "cmd-palette-label";
+const paletteInputId = "cmd-palette-input";
+const paletteListboxId = "cmd-palette-listbox";
 
 function saveFocus() {
+  if (previouslyFocused) {
+    return;
+  }
   previouslyFocused = document.activeElement;
 }
 
 function restoreFocus() {
-  if (previouslyFocused && previouslyFocused instanceof HTMLElement) {
-    requestAnimationFrame(() => previouslyFocused && (previouslyFocused as HTMLElement).focus());
-  }
+  const target = previouslyFocused;
   previouslyFocused = null;
+  activeDialog = null;
+  if (target instanceof HTMLElement && target.isConnected) {
+    requestAnimationFrame(() => {
+      if (target.isConnected) {
+        target.focus();
+      }
+    });
+  }
 }
 
 function selectItem(item: PaletteItem, props: CommandPaletteProps) {
@@ -157,6 +181,14 @@ function selectItem(item: PaletteItem, props: CommandPaletteProps) {
   restoreFocus();
 }
 
+function closePalette(props: CommandPaletteProps) {
+  if (!activeDialog) {
+    return;
+  }
+  props.onToggle();
+  restoreFocus();
+}
+
 function scrollActiveIntoView() {
   requestAnimationFrame(() => {
     const el = document.querySelector(".cmd-palette__item--active");
@@ -164,7 +196,41 @@ function scrollActiveIntoView() {
   });
 }
 
+function trapFocus(event: KeyboardEvent, root: HTMLElement) {
+  const focusable = [...root.querySelectorAll<HTMLElement>(FOCUSABLE_SELECTOR)].filter(
+    (element) => element.isConnected && element.tabIndex >= 0 && !element.closest("[hidden]"),
+  );
+  if (focusable.length === 0) {
+    event.preventDefault();
+    root.focus();
+    return;
+  }
+
+  const active = document.activeElement instanceof HTMLElement ? document.activeElement : null;
+  const first = focusable[0];
+  const last = focusable[focusable.length - 1];
+  const focusInside = active ? focusable.includes(active) : false;
+
+  if (event.shiftKey && (!focusInside || active === first)) {
+    event.preventDefault();
+    last.focus();
+    return;
+  }
+  if (!event.shiftKey && (!focusInside || active === last)) {
+    event.preventDefault();
+    first.focus();
+  }
+}
+
 function handleKeydown(e: KeyboardEvent, props: CommandPaletteProps) {
+  if (e.key === "Tab") {
+    const dialog = (e.currentTarget as HTMLElement | null)?.closest("dialog");
+    if (dialog instanceof HTMLElement) {
+      trapFocus(e, dialog);
+    }
+    return;
+  }
+
   const items = filteredItems(props.query);
   if (items.length === 0 && (e.key === "ArrowDown" || e.key === "ArrowUp" || e.key === "Enter")) {
     return;
@@ -188,8 +254,8 @@ function handleKeydown(e: KeyboardEvent, props: CommandPaletteProps) {
       break;
     case "Escape":
       e.preventDefault();
-      props.onToggle();
-      restoreFocus();
+      e.stopPropagation();
+      closePalette(props);
       break;
   }
 }
@@ -207,10 +273,44 @@ function getCategoryLabel(category: string): string {
   }
 }
 
-function focusInput(el: Element | undefined) {
-  if (el) {
+function getOptionId(item: PaletteItem): string {
+  return `cmd-palette-option-${item.id.replace(/[^a-zA-Z0-9_-]/g, "-")}`;
+}
+
+function syncDialog(el: Element | undefined) {
+  if (!(el instanceof HTMLDialogElement)) {
+    if (activeDialog) {
+      restoreFocus();
+    }
+    return;
+  }
+  if (activeDialog !== el) {
     saveFocus();
-    requestAnimationFrame(() => (el as HTMLInputElement).focus());
+    activeDialog = el;
+  }
+  if (el.open) {
+    return;
+  }
+  if (typeof el.showModal === "function") {
+    try {
+      el.removeAttribute("aria-modal");
+      el.showModal();
+      return;
+    } catch {
+      // Fall through to the open attribute fallback below.
+    }
+  }
+  el.setAttribute("aria-modal", "true");
+  el.setAttribute("open", "");
+}
+
+function focusInput(el: Element | undefined) {
+  if (el instanceof HTMLInputElement) {
+    requestAnimationFrame(() => {
+      if (el.isConnected) {
+        el.focus();
+      }
+    });
   }
 }
 
@@ -221,13 +321,23 @@ export function renderCommandPalette(props: CommandPaletteProps) {
 
   const items = filteredItems(props.query);
   const grouped = groupItems(items);
+  const activeItem = items[props.activeIndex];
+  const activeOptionId = activeItem ? getOptionId(activeItem) : nothing;
+  const paletteLabel = t("overview.palette.placeholder");
 
   return html`
-    <div
+    <dialog
+      ${ref(syncDialog)}
       class="cmd-palette-overlay"
-      @click=${() => {
-        props.onToggle();
-        restoreFocus();
+      aria-labelledby=${paletteDialogLabelId}
+      @cancel=${(e: Event) => {
+        e.preventDefault();
+        closePalette(props);
+      }}
+      @click=${(e: Event) => {
+        if (e.target === e.currentTarget) {
+          closePalette(props);
+        }
       }}
     >
       <div
@@ -235,17 +345,26 @@ export function renderCommandPalette(props: CommandPaletteProps) {
         @click=${(e: Event) => e.stopPropagation()}
         @keydown=${(e: KeyboardEvent) => handleKeydown(e, props)}
       >
+        <label id=${paletteDialogLabelId} class="cmd-palette__label" for=${paletteInputId}
+          >${paletteLabel}</label
+        >
         <input
           ${ref(focusInput)}
+          id=${paletteInputId}
           class="cmd-palette__input"
-          placeholder="${t("overview.palette.placeholder")}"
+          role="combobox"
+          aria-autocomplete="list"
+          aria-controls=${paletteListboxId}
+          aria-activedescendant=${activeOptionId}
+          aria-expanded="true"
+          placeholder=${paletteLabel}
           .value=${props.query}
           @input=${(e: Event) => {
             props.onQueryChange((e.target as HTMLInputElement).value);
             props.onActiveIndexChange(0);
           }}
         />
-        <div class="cmd-palette__results">
+        <div id=${paletteListboxId} class="cmd-palette__results" role="listbox">
           ${grouped.length === 0
             ? html`<div class="cmd-palette__empty">
                 <span class="nav-item__icon" style="opacity:0.3;width:20px;height:20px"
@@ -261,7 +380,10 @@ export function renderCommandPalette(props: CommandPaletteProps) {
                     const isActive = globalIndex === props.activeIndex;
                     return html`
                       <div
+                        id=${getOptionId(item)}
                         class="cmd-palette__item ${isActive ? "cmd-palette__item--active" : ""}"
+                        role="option"
+                        aria-selected=${isActive ? "true" : "false"}
                         @click=${(e: Event) => {
                           e.stopPropagation();
                           selectItem(item, props);
@@ -287,6 +409,6 @@ export function renderCommandPalette(props: CommandPaletteProps) {
           <span><kbd>esc</kbd> ${t("overview.palette.footer.close")}</span>
         </div>
       </div>
-    </div>
+    </dialog>
   `;
 }