feat(crypto): QR-code device verification (alongside emoji SAS)

B2 of the Matrix protocol-gaps roadmap, gate-green (688 tests):
- Enable QR verification methods (show/scan/reciprocate) in initMatrix.
- Extend DeviceVerification: the Ready step offers your own QR (byte-mode encode
  via qrcode), a camera 'Scan their QR code' flow, and an emoji fallback; the
  Started step routes reciprocate → a confirm step (useVerifierShowReciprocateQr)
  or SAS as before.
- New QrScanner component: getUserMedia + jsQR, handing the raw binaryData bytes
  to request.scanQRCode (BarcodeDetector is string-only, so can't be used).
- Adds qrcode + jsqr (small, pure-JS, client-only); build-verified under rolldown.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

LOTUS_TESTING.md

@@ -675,6 +675,8 @@ Run the axe DevTools extension (or Lighthouse → Accessibility) on a room view,
 
 ## Outstanding verification backlog
 
+**QR Device Verification (2026-07):** With two logged-in Lotus sessions (or Lotus + Element), start a device verification. On the **Ready** step you now see your own QR code plus a **"Scan their QR code"** button and a **"Verify with emoji instead"** fallback. Have one device **scan** the other's code (grant camera permission) → the showing device asks you to **Confirm**, and both reach **verified**. Check: emoji-SAS still works unchanged; denying camera shows a graceful "verify with emojis instead" message; a deliberately-wrong scan cancels cleanly. Desktop (WebView2) auto-grants the camera; web needs the Permissions-Policy camera allowance (already set).
+
 **Disappearing Messages (MSC1763 `m.room.retention`, 2026-07):** In Room Settings → General → **Message Retention**, an admin picks Off / 1 Day / 1 Week / 1 Month (non-admins see the buttons disabled). After setting e.g. 1 Day, messages older than a day **vanish from the timeline** for everyone in Lotus (toggle Settings → General → **Show Hidden Events** to reveal them again). Setting back to **Off** restores them. Separately, each user can enable Settings → General → **Enforce Message Retention** (default OFF) → their OWN expired messages then get **permanently redacted** within ~30 s (verify: OTHER people's messages are NEVER redacted by this; only your own). Note true server-side purge also needs Synapse `retention:` configured.
 
 **Mark as Unread + Low Priority (MSC2867 / m.lowpriority, 2026-07):** Right-click a room in the sidebar → **Mark as Unread** puts a dot on the row (bold name) even with no new messages; opening/reading the room clears it, and it syncs to another device. **Mark as Read** on a marked room clears it too. Right-click → **Add to Low Priority** moves the room into a collapsed "Low Priority" category at the bottom of the room list (and removes it from Favorites if it was there, and vice-versa); **Remove from Low Priority** returns it to Rooms.

LOTUS_TODO.md

@@ -100,10 +100,10 @@ Genuine Matrix client-spec / MSC features Lotus does **not** yet implement (audi
 - [x] **Mark as Unread — MSC2867 `m.marked_unread`.** Room account data `{ unread: true }` (+ unstable `com.famedly.marked_unread`) via `mx.setRoomAccountData`; clear on read. Context-menu item in `RoomNavItem` + light the existing unread dot; integrate `state/room/roomToUnread.ts`.
 - [x] **Low Priority rooms — `m.lowpriority` tag.** Mirror the favourite impl (`RoomNavItem.tsx:331-337` `setRoomTag/deleteRoomTag` + the favourites category in `home/Home.tsx`): context-menu toggle + a collapsed "Low Priority" category sorted to the bottom, excluded from normal unread nudging.
 
-**Phase B:**
+**Phase B ✅ (2026-07, gate-green 688 tests):**
 
-- [ ] **Disappearing Messages — MSC1763 `m.room.retention`.** PL-gated room-settings `SettingTile` to set `{ max_lifetime }`; retention badge; a client-side sweep hides/self-redacts own expired events (pattern like the mute-timer restore in `ClientNonUIFeatures.tsx`). True server deletion also wants Synapse `retention:` (LXC 151).
+- [x] **Disappearing Messages — MSC1763 `m.room.retention`.** PL-gated room-settings `SettingTile` to set `{ max_lifetime }`; retention badge; a client-side sweep hides/self-redacts own expired events (pattern like the mute-timer restore in `ClientNonUIFeatures.tsx`). True server deletion also wants Synapse `retention:` (LXC 151).
-- [ ] **QR Device Verification — reciprocate QR.** Add the QR path beside emoji-SAS in `components/DeviceVerification.tsx`: render with `qrcode.react` (already a dep), scan via `BarcodeDetector` (fallback `jsQR`); uses the SDK `VerificationRequest` QR/reciprocate support.
+- [x] **QR Device Verification — reciprocate QR.** Add the QR path beside emoji-SAS in `components/DeviceVerification.tsx`: render with `qrcode.react` (already a dep), scan via `BarcodeDetector` (fallback `jsQR`); uses the SDK `VerificationRequest` QR/reciprocate support.
 
 **Phase C (large — each its own planning session):**
 

package-lock.json

@@ -49,6 +49,7 @@
         "immer": "11.1.8",
         "is-hotkey": "0.2.0",
         "jotai": "2.20.0",
+        "jsqr": "1.4.0",
         "katex": "0.16.11",
         "linkify-react": "4.3.3",
         "linkifyjs": "4.3.3",
@@ -57,6 +58,7 @@
         "millify": "6.1.0",
         "pdfjs-dist": "5.7.284",
         "prismjs": "1.30.0",
+        "qrcode": "1.5.4",
         "qrcode.react": "4.2.0",
         "react": "19.2.6",
         "react-aria": "3.48.0",
@@ -87,6 +89,7 @@
         "@types/katex": "0.16.8",
         "@types/node": "25.9.1",
         "@types/prismjs": "1.26.6",
+        "@types/qrcode": "1.5.6",
         "@types/react": "19.2.15",
         "@types/react-dom": "19.2.3",
         "@types/react-google-recaptcha": "2.1.9",
@@ -3990,6 +3993,16 @@
       "dev": true,
       "license": "MIT"
     },
+    "node_modules/@types/qrcode": {
+      "version": "1.5.6",
+      "resolved": "https://registry.npmjs.org/@types/qrcode/-/qrcode-1.5.6.tgz",
+      "integrity": "sha512-te7NQcV2BOvdj2b1hCAHzAoMNuj65kNBMz0KBaxM6c3VGBOhU0dURQKOtH8CFNI/dsKkwlv32p26qYQTWoB5bw==",
+      "dev": true,
+      "license": "MIT",
+      "dependencies": {
+        "@types/node": "*"
+      }
+    },
     "node_modules/@types/react": {
       "version": "19.2.15",
       "resolved": "https://registry.npmjs.org/@types/react/-/react-19.2.15.tgz",
@@ -5171,6 +5184,15 @@
         "node": ">=6"
       }
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+    "node_modules/camelcase": {
+      "version": "5.3.1",
+      "resolved": "https://registry.npmjs.org/camelcase/-/camelcase-5.3.1.tgz",
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+      "license": "MIT",
+      "engines": {
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+    },
     "node_modules/camelize": {
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@@ -5965,6 +5987,15 @@
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+    "node_modules/decamelize": {
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+      "resolved": "https://registry.npmjs.org/decamelize/-/decamelize-1.2.0.tgz",
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+      "license": "MIT",
+      "engines": {
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@@ -6108,6 +6139,12 @@
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+    "node_modules/dijkstrajs": {
+      "version": "1.0.3",
+      "resolved": "https://registry.npmjs.org/dijkstrajs/-/dijkstrajs-1.0.3.tgz",
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+      "license": "MIT"
+    },
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@@ -9057,6 +9094,12 @@
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       }
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+    "node_modules/jsqr": {
+      "version": "1.4.0",
+      "resolved": "https://registry.npmjs.org/jsqr/-/jsqr-1.4.0.tgz",
+      "integrity": "sha512-dxLob7q65Xg2DvstYkRpkYtmKm2sPJ9oFhrhmudT1dZvNFFTlroai3AWSpLey/w5vMcLBXRgOJsbXpdN9HzU/A==",
+      "license": "Apache-2.0"
+    },
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@@ -10500,6 +10543,15 @@
         "url": "https://github.com/sponsors/sindresorhus"
       }
     },
+    "node_modules/p-try": {
+      "version": "2.2.0",
+      "resolved": "https://registry.npmjs.org/p-try/-/p-try-2.2.0.tgz",
+      "integrity": "sha512-R4nPAVTAU0B9D35/Gk3uJf/7XYbQcyohSKdvAxIRSNghFl4e71hVoGnBNQz9cWaXxO2I10KTC+3jMdvvoKw6dQ==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=6"
+      }
+    },
     "node_modules/package-json-from-dist": {
       "version": "1.0.1",
       "resolved": "https://registry.npmjs.org/package-json-from-dist/-/package-json-from-dist-1.0.1.tgz",
@@ -10537,7 +10589,6 @@
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-      "dev": true,
       "engines": {
         "node": ">=8"
       }
@@ -10652,6 +10703,15 @@
         "pathe": "^2.0.1"
       }
     },
+    "node_modules/pngjs": {
+      "version": "5.0.0",
+      "resolved": "https://registry.npmjs.org/pngjs/-/pngjs-5.0.0.tgz",
+      "integrity": "sha512-40QW5YalBNfQo5yRYmiw7Yz6TKKVr3h6970B2YE+3fQpsWcrbj1PzJgxeJ19DRQjhMbKPIuMY8rFaXc8moolVw==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=10.13.0"
+      }
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@@ -10759,6 +10819,23 @@
         "node": ">=6"
       }
     },
+    "node_modules/qrcode": {
+      "version": "1.5.4",
+      "resolved": "https://registry.npmjs.org/qrcode/-/qrcode-1.5.4.tgz",
+      "integrity": "sha512-1ca71Zgiu6ORjHqFBDpnSMTR2ReToX4l1Au1VFLyVeBTFavzQnv5JxMFr3ukHVKpSrSA2MCk0lNJSykjUfz7Zg==",
+      "license": "MIT",
+      "dependencies": {
+        "dijkstrajs": "^1.0.1",
+        "pngjs": "^5.0.0",
+        "yargs": "^15.3.1"
+      },
+      "bin": {
+        "qrcode": "bin/qrcode"
+      },
+      "engines": {
+        "node": ">=10.13.0"
+      }
+    },
     "node_modules/qrcode.react": {
       "version": "4.2.0",
       "resolved": "https://registry.npmjs.org/qrcode.react/-/qrcode.react-4.2.0.tgz",
@@ -10768,6 +10845,124 @@
         "react": "^16.8.0 || ^17.0.0 || ^18.0.0 || ^19.0.0"
       }
     },
+    "node_modules/qrcode/node_modules/cliui": {
+      "version": "6.0.0",
+      "resolved": "https://registry.npmjs.org/cliui/-/cliui-6.0.0.tgz",
+      "integrity": "sha512-t6wbgtoCXvAzst7QgXxJYqPt0usEfbgQdftEPbLL/cvv6HPE5VgvqCuAIDR0NgU52ds6rFwqrgakNLrHEjCbrQ==",
+      "license": "ISC",
+      "dependencies": {
+        "string-width": "^4.2.0",
+        "strip-ansi": "^6.0.0",
+        "wrap-ansi": "^6.2.0"
+      }
+    },
+    "node_modules/qrcode/node_modules/find-up": {
+      "version": "4.1.0",
+      "resolved": "https://registry.npmjs.org/find-up/-/find-up-4.1.0.tgz",
+      "integrity": "sha512-PpOwAdQ/YlXQ2vj8a3h8IipDuYRi3wceVQQGYWxNINccq40Anw7BlsEXCMbt1Zt+OLA6Fq9suIpIWD0OsnISlw==",
+      "license": "MIT",
+      "dependencies": {
+        "locate-path": "^5.0.0",
+        "path-exists": "^4.0.0"
+      },
+      "engines": {
+        "node": ">=8"
+      }
+    },
+    "node_modules/qrcode/node_modules/locate-path": {
+      "version": "5.0.0",
+      "resolved": "https://registry.npmjs.org/locate-path/-/locate-path-5.0.0.tgz",
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+      "license": "MIT",
+      "dependencies": {
+        "p-try": "^2.0.0"
+      },
+      "engines": {
+        "node": ">=6"
+      },
+      "funding": {
+        "url": "https://github.com/sponsors/sindresorhus"
+      }
+    },
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+      "dependencies": {
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+      "engines": {
+        "node": ">=8"
+      }
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+      "license": "MIT",
+      "dependencies": {
+        "ansi-styles": "^4.0.0",
+        "string-width": "^4.1.0",
+        "strip-ansi": "^6.0.0"
+      },
+      "engines": {
+        "node": ">=8"
+      }
+    },
+    "node_modules/qrcode/node_modules/y18n": {
+      "version": "4.0.3",
+      "resolved": "https://registry.npmjs.org/y18n/-/y18n-4.0.3.tgz",
+      "integrity": "sha512-JKhqTOwSrqNA1NY5lSztJ1GrBiUodLMmIZuLiDaMRJ+itFd+ABVE8XBjOvIWL+rSqNDC74LCSFmlb/U4UZ4hJQ==",
+      "license": "ISC"
+    },
+    "node_modules/qrcode/node_modules/yargs": {
+      "version": "15.4.1",
+      "resolved": "https://registry.npmjs.org/yargs/-/yargs-15.4.1.tgz",
+      "integrity": "sha512-aePbxDmcYW++PaqBsJ+HYUFwCdv4LVvdnhBy78E57PIor8/OVvhMrADFFEDh8DHDFRv/O9i3lPhsENjO7QX0+A==",
+      "license": "MIT",
+      "dependencies": {
+        "cliui": "^6.0.0",
+        "decamelize": "^1.2.0",
+        "find-up": "^4.1.0",
+        "get-caller-file": "^2.0.1",
+        "require-directory": "^2.1.1",
+        "require-main-filename": "^2.0.0",
+        "set-blocking": "^2.0.0",
+        "string-width": "^4.2.0",
+        "which-module": "^2.0.0",
+        "y18n": "^4.0.0",
+        "yargs-parser": "^18.1.2"
+      },
+      "engines": {
+        "node": ">=8"
+      }
+    },
+    "node_modules/qrcode/node_modules/yargs-parser": {
+      "version": "18.1.3",
+      "resolved": "https://registry.npmjs.org/yargs-parser/-/yargs-parser-18.1.3.tgz",
+      "integrity": "sha512-o50j0JeToy/4K6OZcaQmW6lyXXKhq7csREXcDwk2omFPJEwUNOVtJKvmDr9EI1fAJZUyZcRF7kxGBWmRXudrCQ==",
+      "license": "ISC",
+      "dependencies": {
+        "camelcase": "^5.0.0",
+        "decamelize": "^1.2.0"
+      },
+      "engines": {
+        "node": ">=6"
+      }
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     "node_modules/raf-schd": {
       "version": "4.0.3",
       "resolved": "https://registry.npmjs.org/raf-schd/-/raf-schd-4.0.3.tgz",
@@ -11188,6 +11383,12 @@
         "node": "*"
       }
     },
+    "node_modules/require-main-filename": {
+      "version": "2.0.0",
+      "resolved": "https://registry.npmjs.org/require-main-filename/-/require-main-filename-2.0.0.tgz",
+      "integrity": "sha512-NKN5kMDylKuldxYLSUfrbo5Tuzh4hd+2E8NPPX02mZtn1VuREQToYe/ZdlJy+J3uCpfaiGF05e7B8W0iXbQHmg==",
+      "license": "ISC"
+    },
     "node_modules/resize-observer-polyfill": {
       "version": "1.5.1",
       "resolved": "https://registry.npmjs.org/resize-observer-polyfill/-/resize-observer-polyfill-1.5.1.tgz",
@@ -11518,6 +11719,12 @@
         "node": ">=20.0.0"
       }
     },
+    "node_modules/set-blocking": {
+      "version": "2.0.0",
+      "resolved": "https://registry.npmjs.org/set-blocking/-/set-blocking-2.0.0.tgz",
+      "integrity": "sha512-KiKBS8AnWGEyLzofFfmvKwpdPzqiy16LvQfK3yv/fVH7Bj13/wl3JSR1J+rfgRE9q7xUJK4qvgS8raSOeLUehw==",
+      "license": "ISC"
+    },
     "node_modules/set-cookie-parser": {
       "version": "2.7.2",
       "resolved": "https://registry.npmjs.org/set-cookie-parser/-/set-cookie-parser-2.7.2.tgz",
@@ -12983,6 +13190,12 @@
         "url": "https://github.com/sponsors/ljharb"
       }
     },
+    "node_modules/which-module": {
+      "version": "2.0.1",
+      "resolved": "https://registry.npmjs.org/which-module/-/which-module-2.0.1.tgz",
+      "integrity": "sha512-iBdZ57RDvnOR9AGBhML2vFZf7h8vmBjhoaZqODJBFWHVtKkDmKuHai3cx5PgVMrX5YDNp27AofYbAwctSS+vhQ==",
+      "license": "ISC"
+    },
     "node_modules/which-typed-array": {
       "version": "1.1.20",
       "resolved": "https://registry.npmjs.org/which-typed-array/-/which-typed-array-1.1.20.tgz",

package.json

@@ -74,6 +74,7 @@
     "immer": "11.1.8",
     "is-hotkey": "0.2.0",
     "jotai": "2.20.0",
+    "jsqr": "1.4.0",
     "katex": "0.16.11",
     "linkify-react": "4.3.3",
     "linkifyjs": "4.3.3",
@@ -82,6 +83,7 @@
     "millify": "6.1.0",
     "pdfjs-dist": "5.7.284",
     "prismjs": "1.30.0",
+    "qrcode": "1.5.4",
     "qrcode.react": "4.2.0",
     "react": "19.2.6",
     "react-aria": "3.48.0",
@@ -112,6 +114,7 @@
     "@types/katex": "0.16.8",
     "@types/node": "25.9.1",
     "@types/prismjs": "1.26.6",
+    "@types/qrcode": "1.5.6",
     "@types/react": "19.2.15",
     "@types/react-dom": "19.2.3",
     "@types/react-google-recaptcha": "2.1.9",

src/app/components/DeviceVerification.tsx

@@ -1,12 +1,14 @@
 import {
+  ShowQrCodeCallbacks,
   ShowSasCallbacks,
   VerificationPhase,
   VerificationRequest,
   Verifier,
 } from 'matrix-js-sdk/lib/crypto-api';
-import React, { CSSProperties, useCallback, useEffect, useState } from 'react';
+import React, { CSSProperties, useCallback, useEffect, useRef, useState } from 'react';
 import { useTranslation } from 'react-i18next';
 import { VerificationMethod } from 'matrix-js-sdk/lib/types';
+import QRCode from 'qrcode';
 import {
   Box,
   Button,
@@ -27,11 +29,13 @@ import {
   useVerificationRequestPhase,
   useVerificationRequestReceived,
   useVerifierCancel,
+  useVerifierShowReciprocateQr,
   useVerifierShowSas,
 } from '../hooks/useVerificationRequest';
 import { AsyncStatus, useAsyncCallback } from '../hooks/useAsyncCallback';
 import { ContainerColor } from '../styles/ContainerColor.css';
 import { useModalStyle } from '../hooks/useModalStyle';
+import { QrScanner } from './QrScanner';
 
 const DialogHeaderStyles: CSSProperties = {
   padding: `0 ${config.space.S200} 0 ${config.space.S400}`,
@@ -97,32 +101,6 @@ function VerificationAccept({ onAccept }: VerificationAcceptProps) {
   );
 }
 
-function VerificationWaitStart() {
-  const { t } = useTranslation();
-  return (
-    <Box direction="Column" gap="400">
-      <Text>{t('Organisms.DeviceVerification.request_accepted')}</Text>
-      <WaitingMessage message={t('Organisms.DeviceVerification.waiting_response')} />
-    </Box>
-  );
-}
-
-type VerificationStartProps = {
-  onStart: () => Promise<void>;
-};
-function AutoVerificationStart({ onStart }: VerificationStartProps) {
-  const { t } = useTranslation();
-  useEffect(() => {
-    onStart();
-  }, [onStart]);
-
-  return (
-    <Box direction="Column" gap="400">
-      <WaitingMessage message={t('Organisms.DeviceVerification.starting_emoji')} />
-    </Box>
-  );
-}
-
 function CompareEmoji({ sasData }: { sasData: ShowSasCallbacks }) {
   const { t } = useTranslation();
   const [confirmState, confirm] = useAsyncCallback(useCallback(() => sasData.confirm(), [sasData]));
@@ -237,6 +215,120 @@ function VerificationCanceled({ onClose }: VerificationCanceledProps) {
   );
 }
 
+function QrCodeImage({ data }: { data: Uint8ClampedArray }) {
+  const canvasRef = useRef<HTMLCanvasElement>(null);
+  useEffect(() => {
+    const canvas = canvasRef.current;
+    if (!canvas) return;
+    // Byte-mode so the raw verification bytes round-trip (a string value would
+    // mangle high bytes via UTF-8).
+    QRCode.toCanvas(canvas, [{ data: new Uint8Array(data), mode: 'byte' }], {
+      width: 220,
+      margin: 2,
+      color: { dark: '#000000', light: '#ffffff' },
+    }).catch(() => undefined);
+  }, [data]);
+  return (
+    <Box justifyContent="Center">
+      <canvas ref={canvasRef} style={{ borderRadius: config.radii.R300 }} />
+    </Box>
+  );
+}
+
+type VerificationReadyProps = {
+  request: VerificationRequest;
+  onStartSas: () => void;
+  onScanned: (bytes: Uint8ClampedArray) => void;
+};
+function VerificationReady({ request, onStartSas, onScanned }: VerificationReadyProps) {
+  const [myQr, setMyQr] = useState<Uint8ClampedArray>();
+  const [scanning, setScanning] = useState(false);
+  const canShowMine = request.otherPartySupportsMethod(VerificationMethod.ScanQrCode);
+  const canScanTheirs = request.otherPartySupportsMethod(VerificationMethod.ShowQrCode);
+
+  useEffect(() => {
+    if (!canShowMine) return;
+    request
+      .generateQRCode()
+      .then((bytes) => {
+        if (bytes) setMyQr(bytes);
+      })
+      .catch(() => undefined);
+  }, [request, canShowMine]);
+
+  if (scanning) {
+    return <QrScanner onScan={onScanned} onCancel={() => setScanning(false)} />;
+  }
+
+  return (
+    <Box direction="Column" gap="400">
+      {myQr && (
+        <Box direction="Column" gap="200">
+          <Text size="T300">Scan this code with your other device to verify.</Text>
+          <QrCodeImage data={myQr} />
+        </Box>
+      )}
+      <Box direction="Column" gap="200">
+        {canScanTheirs && (
+          <Button variant="Primary" fill="Solid" onClick={() => setScanning(true)}>
+            <Text size="B400">Scan their QR code</Text>
+          </Button>
+        )}
+        <Button variant="Secondary" fill="Soft" onClick={onStartSas}>
+          <Text size="B400">Verify with emoji instead</Text>
+        </Button>
+      </Box>
+    </Box>
+  );
+}
+
+type ReciprocateVerificationProps = {
+  verifier: Verifier;
+  onCancel: () => void;
+};
+function ReciprocateVerification({ verifier, onCancel }: ReciprocateVerificationProps) {
+  const [qrCallbacks, setQrCallbacks] = useState<ShowQrCodeCallbacks>();
+  const [confirmState, confirm] = useAsyncCallback(
+    useCallback(async () => qrCallbacks?.confirm(), [qrCallbacks]),
+  );
+
+  useVerifierShowReciprocateQr(verifier, setQrCallbacks);
+  useVerifierCancel(verifier, onCancel);
+
+  const confirming =
+    confirmState.status === AsyncStatus.Loading || confirmState.status === AsyncStatus.Success;
+
+  // The showing side gets ShowReciprocateQr callbacks after the other device
+  // scans; the scanning side never does (it already called verify()) and just
+  // waits for completion.
+  if (!qrCallbacks) {
+    return (
+      <Box direction="Column" gap="400">
+        <WaitingMessage message="Verifying…" />
+      </Box>
+    );
+  }
+
+  return (
+    <Box direction="Column" gap="400">
+      <Text>The other device scanned this code. Confirm it now shows as verified.</Text>
+      <Box direction="Column" gap="200">
+        <Button variant="Primary" fill="Soft" onClick={confirm} disabled={confirming}>
+          <Text size="B400">Confirm</Text>
+        </Button>
+        <Button
+          variant="Primary"
+          fill="Soft"
+          onClick={() => qrCallbacks.cancel()}
+          disabled={confirming}
+        >
+          <Text size="B400">Cancel</Text>
+        </Button>
+      </Box>
+    </Box>
+  );
+}
+
 type DeviceVerificationProps = {
   request: VerificationRequest;
   onExit: () => void;
@@ -256,6 +348,17 @@ export function DeviceVerification({ request, onExit }: DeviceVerificationProps)
   const handleStart = useCallback(async () => {
     await request.startVerification(VerificationMethod.Sas);
   }, [request]);
+  const handleScanned = useCallback(
+    async (bytes: Uint8ClampedArray) => {
+      try {
+        const verifier = await request.scanQRCode(bytes);
+        await verifier.verify();
+      } catch {
+        // A bad/mismatched scan cancels the request; the Cancelled phase renders.
+      }
+    },
+    [request],
+  );
 
   return (
     <Overlay open backdrop={<OverlayBackdrop />}>
@@ -290,15 +393,20 @@ export function DeviceVerification({ request, onExit }: DeviceVerificationProps)
                 ) : (
                   <VerificationAccept onAccept={handleAccept} />
                 ))}
-              {phase === VerificationPhase.Ready &&
+              {phase === VerificationPhase.Ready && (
-                (request.initiatedByMe ? (
+                <VerificationReady
-                  <AutoVerificationStart onStart={handleStart} />
+                  request={request}
-                ) : (
+                  onStartSas={handleStart}
-                  <VerificationWaitStart />
+                  onScanned={handleScanned}
-                ))}
+                />
+              )}
               {phase === VerificationPhase.Started &&
                 (request.verifier ? (
-                  <SasVerification verifier={request.verifier} onCancel={handleCancel} />
+                  request.chosenMethod === VerificationMethod.Reciprocate ? (
+                    <ReciprocateVerification verifier={request.verifier} onCancel={handleCancel} />
+                  ) : (
+                    <SasVerification verifier={request.verifier} onCancel={handleCancel} />
+                  )
                 ) : (
                   <VerificationUnexpected
                     message="Unexpected Error! Verification is started but verifier is missing."

src/app/components/QrScanner.tsx

@@ -0,0 +1,101 @@
+import React, { useEffect, useRef, useState } from 'react';
+import { Box, Button, color, config, Text } from 'folds';
+import jsQR from 'jsqr';
+
+type QrScannerProps = {
+  onScan: (bytes: Uint8ClampedArray) => void;
+  onCancel: () => void;
+};
+
+// Camera QR scanner. Decodes frames with jsQR and hands back the raw byte
+// segment (`result.binaryData`) — Matrix QR verification needs the raw bytes,
+// not a decoded string, so the string-only `BarcodeDetector` can't be used.
+export function QrScanner({ onScan, onCancel }: QrScannerProps) {
+  const videoRef = useRef<HTMLVideoElement>(null);
+  const [error, setError] = useState<string>();
+  const doneRef = useRef(false);
+
+  useEffect(() => {
+    let stream: MediaStream | undefined;
+    let raf = 0;
+    const canvas = document.createElement('canvas');
+    const ctx = canvas.getContext('2d', { willReadFrequently: true });
+
+    const tick = () => {
+      const video = videoRef.current;
+      if (!doneRef.current && video && ctx && video.readyState === video.HAVE_ENOUGH_DATA) {
+        canvas.width = video.videoWidth;
+        canvas.height = video.videoHeight;
+        ctx.drawImage(video, 0, 0, canvas.width, canvas.height);
+        const image = ctx.getImageData(0, 0, canvas.width, canvas.height);
+        const result = jsQR(image.data, image.width, image.height);
+        if (result && result.binaryData.length > 0) {
+          doneRef.current = true;
+          onScan(new Uint8ClampedArray(result.binaryData));
+          return;
+        }
+      }
+      raf = requestAnimationFrame(tick);
+    };
+
+    (async () => {
+      try {
+        stream = await navigator.mediaDevices.getUserMedia({
+          video: { facingMode: 'environment' },
+        });
+        if (videoRef.current) {
+          videoRef.current.srcObject = stream;
+          await videoRef.current.play();
+        }
+        raf = requestAnimationFrame(tick);
+      } catch {
+        setError(
+          'Could not access the camera. Grant camera permission, or verify with emojis instead.',
+        );
+      }
+    })();
+
+    return () => {
+      doneRef.current = true;
+      cancelAnimationFrame(raf);
+      stream?.getTracks().forEach((track) => track.stop());
+    };
+  }, [onScan]);
+
+  if (error) {
+    return (
+      <Box direction="Column" gap="400">
+        <Text style={{ color: color.Critical.Main }} size="T300">
+          {error}
+        </Text>
+        <Button variant="Secondary" fill="Soft" onClick={onCancel}>
+          <Text size="B400">Back</Text>
+        </Button>
+      </Box>
+    );
+  }
+
+  return (
+    <Box direction="Column" gap="400" alignItems="Center">
+      <Text size="T300" align="Center">
+        Point your camera at the QR code shown on your other device.
+      </Text>
+      <video
+        ref={videoRef}
+        muted
+        playsInline
+        style={{
+          width: '100%',
+          maxWidth: 280,
+          borderRadius: config.radii.R400,
+          background: '#000',
+        }}
+      >
+        <track kind="captions" />
+      </video>
+      <Button variant="Secondary" fill="Soft" onClick={onCancel}>
+        <Text size="B400">Cancel</Text>
+      </Button>
+    </Box>
+  );
+}

src/client/initMatrix.ts

@@ -38,7 +38,8 @@ export const initClient = async (session: Session): Promise<MatrixClient> => {
     deviceId: session.deviceId,
     timelineSupport: true,
     cryptoCallbacks: cryptoCallbacks as any,
-    verificationMethods: ['m.sas.v1'],
+    // SAS (emoji) + QR-code verification (show/scan/reciprocate).
+    verificationMethods: ['m.sas.v1', 'm.qr_code.show.v1', 'm.qr_code.scan.v1', 'm.reciprocate.v1'],
     tokenRefreshFunction: oidcRefresher
       ? (refreshToken) => oidcRefresher.doRefreshAccessToken(refreshToken)
       : undefined,