Give the level meter one bar size at every width

- A bar and the gap beside it are fixed; how many bars there are follows the
  space. Spread gaps made the meter a different shape everywhere, and closed
  the bars into one block when space ran short.
- Bars that touch cannot be counted, and the count is what carries the level
  without colour.
- `contain: inline-size` and `min-inline-size: 0` so the width decides the
  count and not the reverse — without them the bars set the menu's width.
- Gap is half again the bar width, measured off the design mock: 10px bars
  14px apart, a ratio of 1.4, nearest token pair 4px and 6px.
- Sizes stay in the stylesheet; the component reads them back off a rendered
  bar rather than repeating them.

src/components/MicrophoneLevelMeter.module.css

@@ -27,12 +27,28 @@ Please see LICENSE in the repository root for full details.
 }
 
 .segments {
-  /* Spans the menu by spreading the gaps, so the bars keep their proportion
-     instead of growing to fill the space. */
+  /* A bar and the space beside it are always the same size; what changes with
+     the width available is how many bars there are. Spreading a fixed number of
+     bars instead would make the meter a different shape in every place it is
+     used, and close them up into one solid block wherever the space ran short —
+     and a meter whose bars touch stops reading as a count, which is what
+     carries the level for anyone who cannot rely on the colour.
+
+     Both sizes are set here and nowhere else: the component reads them back off
+     the rendered bars to work out how many fit. */
   flex: 1;
+  /* The width decides the count, never the other way round. Containment is
+     what enforces that: without it the bars are both a floor under the width
+     and the widest thing in the menu, so the meter would set the menu's width
+     and the device names — which are what a person is reading — would have to
+     fit around it. */
+  contain: inline-size;
+  min-inline-size: 0;
   display: flex;
   align-items: center;
-  justify-content: space-between;
+  /* Half again as wide as a bar, as the design has it: bars set as close as
+     their own width read as a solid block long before they touch. */
+  gap: var(--cpd-space-1-5x);
 }
 
 .segment {

src/components/MicrophoneLevelMeter.stories.tsx

@@ -0,0 +1,178 @@
+/*
+Copyright 2026 Element Creations Ltd.
+
+SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
+Please see LICENSE in the repository root for full details.
+*/
+
+import { expect, within } from "storybook/test";
+import { type JSX } from "react";
+
+import type { Meta, StoryObj } from "@storybook/react-vite";
+import {
+  MicrophoneLevelMeter,
+  type MicrophoneLevelMeterProps,
+} from "./MicrophoneLevelMeter";
+import styles from "./MicrophoneLevelMeter.module.css";
+import { METER_SEGMENTS } from "../state/MicrophoneLevel";
+
+/**
+ * A width to show the meter at, close to the menu it lives in.
+ *
+ * Not a copy of the menu's width, and nothing depends on the two agreeing: a
+ * bar and the gap beside it are a fixed size now, so this only decides how many
+ * bars there is room for. Without a width at all the stories would shrink-wrap
+ * to almost nothing and show a meter two bars wide, which is no use to anyone
+ * looking at them.
+ */
+const STORY_WIDTH = 256;
+
+const meta = {
+  component: MicrophoneLevelMeter,
+  decorators: [
+    (Story): JSX.Element => (
+      <div style={{ inlineSize: STORY_WIDTH }}>
+        <Story />
+      </div>
+    ),
+  ],
+  argTypes: {
+    state: {
+      description:
+        "What the selected microphone can say about itself: a level, or a reason there is none.",
+    },
+  },
+} satisfies Meta<typeof MicrophoneLevelMeter>;
+
+export default meta;
+type Story = StoryObj<typeof meta>;
+
+/**
+ * A quiet room. Nothing is lit: room hiss below the noise floor must not read
+ * as "it can hear me".
+ */
+export const Silent: Story = {
+  args: { state: { type: "level", level: 0 } },
+  play: async ({ canvasElement }) => {
+    await expect(litSegments(canvasElement)).toBe(0);
+  },
+};
+
+export const QuietSpeech: Story = {
+  args: { state: { type: "level", level: 5 } },
+};
+
+export const NormalSpeech: Story = {
+  args: { state: { type: "level", level: 12 } },
+  play: async ({ canvasElement }) => {
+    // Shown at something like the width of the menu, so the meter in a story
+    // reads like the meter in a call rather than like a handful of bars. The
+    // design's own mock has sixteen of them at this width; a floor rather than
+    // a count, because the number follows from the bar and gap sizes and those
+    // are the design's to change.
+    await expect(
+      canvasElement.getElementsByClassName(styles.segment).length,
+    ).toBeGreaterThanOrEqual(15);
+  },
+};
+
+export const LoudSpeech: Story = {
+  args: { state: { type: "level", level: METER_SEGMENTS } },
+};
+
+/**
+ * The three volumes differ by how many bars are lit, so the level survives
+ * greyscale and a screen reader as well as it survives colour.
+ */
+export const VolumesAreDistinguishable: Story = {
+  args: { state: { type: "level", level: 5 } },
+  play: async ({ canvasElement, mount }) => {
+    const lit: number[] = [];
+    for (const level of [5, 12, METER_SEGMENTS]) {
+      await mount(<MicrophoneLevelMeter state={{ type: "level", level }} />);
+      lit.push(litSegments(canvasElement));
+      await expect(within(canvasElement).getByRole("meter")).toHaveAttribute(
+        "aria-valuenow",
+        String(level),
+      );
+    }
+    // Three different counts, rising: the level is carried by how many bars
+    // are lit, not by their colour alone.
+    await expect(new Set(lit).size).toBe(lit.length);
+    await expect(lit).toEqual([...lit].sort((a, b) => a - b));
+  },
+};
+
+/**
+ * Permission refused. A message with a next action, never a still meter that
+ * reads as silence.
+ */
+export const PermissionDenied: Story = {
+  args: { state: { type: "permission-denied" } },
+  play: async ({ canvasElement }) => {
+    const canvas = within(canvasElement);
+    await expect(canvas.queryByRole("meter")).toBeNull();
+    await expect(
+      canvas.getByText(/Allow access in your browser settings/),
+    ).toBeVisible();
+  },
+};
+
+/** No input device at all, told apart from a refusal. */
+export const NoDevice: Story = {
+  args: { state: { type: "no-device" } },
+  play: async ({ canvasElement }) => {
+    const canvas = within(canvasElement);
+    await expect(canvas.queryByRole("meter")).toBeNull();
+    await expect(canvas.getByText(/No microphone found/)).toBeVisible();
+  },
+};
+
+/**
+ * The same meter at two widths.
+ *
+ * A bar and the space beside it are always the same size; what changes is how
+ * many bars there are. Spreading a fixed number of bars instead would make the
+ * meter a different shape in every place it is used, and close the bars up into
+ * one block wherever the space ran short — and bars that touch cannot be
+ * counted, which is what carries the level without colour.
+ */
+export const ShapeStaysTheSameAtAnyWidth: Story = {
+  args: { state: { type: "level", level: 12 } },
+  play: async ({ mount, args }) => {
+    const narrow = await measureAt(mount, args, 180);
+    const wide = await measureAt(mount, args, 400);
+
+    await expect(narrow.bar).toBe(wide.bar);
+    await expect(narrow.gap).toBe(wide.gap);
+    await expect(narrow.count).toBeLessThan(wide.count);
+    // And the bars are still bars, not one run of colour.
+    await expect(narrow.gap).toBeGreaterThan(0);
+  },
+};
+
+/** How many bars are painted as carrying level, rather than as empty. */
+function litSegments(canvasElement: HTMLElement): number {
+  return canvasElement.getElementsByClassName(styles.segmentLit).length;
+}
+
+/** Renders the meter at one width and reports the shape of its bars. */
+async function measureAt(
+  mount: (ui: JSX.Element) => Promise<unknown>,
+  args: MicrophoneLevelMeterProps,
+  width: number,
+): Promise<{ count: number; bar: number; gap: number }> {
+  await mount(
+    <div style={{ inlineSize: width }}>
+      <MicrophoneLevelMeter {...args} />
+    </div>,
+  );
+  const bars = Array.from(document.body.getElementsByClassName(styles.segment));
+  const first = bars[0].getBoundingClientRect();
+  const second = bars[1].getBoundingClientRect();
+  return {
+    count: bars.length,
+    bar: first.width,
+    gap: second.left - first.right,
+  };
+}

src/components/MicrophoneLevelMeter.tsx

@@ -5,16 +5,19 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-import { type FC } from "react";
+import { useCallback, useState, type FC } from "react";
 import { Text } from "@vector-im/compound-web";
 import { MicOnIcon } from "@vector-im/compound-design-tokens/assets/web/icons";
 import classNames from "classnames";
 import { useTranslation } from "react-i18next";
 
+import { distinctUntilChanged, map } from "rxjs";
+
 import styles from "./MicrophoneLevelMeter.module.css";
 import { METER_SEGMENTS, type MicrophoneState } from "../state/MicrophoneLevel";
+import { observeElementSize$ } from "../utils/elementSize";
 
-interface Props {
+export interface MicrophoneLevelMeterProps {
   state: MicrophoneState;
   className?: string;
 }
@@ -26,8 +29,29 @@ interface Props {
  * as whether the user is being heard: it keeps moving while muted, and the mute
  * control is what says nothing is transmitted.
  */
-export const MicrophoneLevelMeter: FC<Props> = ({ state, className }) => {
+export const MicrophoneLevelMeter: FC<MicrophoneLevelMeterProps> = ({
+  state,
+  className,
+}) => {
   const { t } = useTranslation();
+  // How many bars there is room for. The bars never change size, so this is
+  // what absorbs a change of width. Starts at the full count so that the first
+  // paint is a meter rather than a single bar, and so that a renderer with no
+  // layout at all — jsdom — still draws the whole thing.
+  const [barCount, setBarCount] = useState(METER_SEGMENTS);
+  const track = useCallback(
+    (element: HTMLDivElement | null): (() => void) | undefined => {
+      if (element === null) return;
+      const subscription = observeElementSize$(element)
+        .pipe(
+          map(({ width }) => barsThatFit(element, width)),
+          distinctUntilChanged(),
+        )
+        .subscribe(setBarCount);
+      return (): void => subscription.unsubscribe();
+    },
+    [],
+  );
 
   if (state.type !== "level")
     return (
@@ -45,6 +69,7 @@ export const MicrophoneLevelMeter: FC<Props> = ({ state, className }) => {
     <div className={classNames(styles.meter, className)}>
       <MicOnIcon width={24} height={24} className={styles.icon} aria-hidden />
       <div
+        ref={track}
         className={styles.segments}
         role="meter"
         aria-label={t("microphone_level.label")}
@@ -56,12 +81,15 @@ export const MicrophoneLevelMeter: FC<Props> = ({ state, className }) => {
           max: METER_SEGMENTS,
         })}
       >
-        {Array.from({ length: METER_SEGMENTS }, (_, i) => (
+        {Array.from({ length: barCount }, (_, i) => (
           <span
             key={i}
             aria-hidden
             className={classNames(styles.segment, {
-              [styles.segmentLit]: i < state.level,
+              // The level is a share of the scale, not a number of bars: how
+              // many bars stand for it depends on how many there are.
+              [styles.segmentLit]:
+                i < Math.round((state.level / METER_SEGMENTS) * barCount),
             })}
           />
         ))}
@@ -69,3 +97,18 @@ export const MicrophoneLevelMeter: FC<Props> = ({ state, className }) => {
     </div>
   );
 };
+
+/**
+ * How many bars fit across `width`, at the size the stylesheet draws them.
+ *
+ * Measured off a rendered bar rather than told: the size of a bar and of the
+ * space beside it are a design question, settled in the stylesheet, and reading
+ * them back is what keeps them from being settled twice.
+ */
+function barsThatFit(track: HTMLElement, width: number): number {
+  const gap = Number.parseFloat(getComputedStyle(track).columnGap);
+  const bar = track.firstElementChild?.getBoundingClientRect().width ?? 0;
+  // A renderer that lays nothing out tells us nothing; keep the full count.
+  if (!(bar > 0) || !(gap >= 0)) return METER_SEGMENTS;
+  return Math.max(1, Math.floor((width + gap) / (bar + gap)));
+}