feat(security): recovery key leaves the clipboard after 60 s, visibly (#156)

useSensitiveCopy: the recovery key's Copy button becomes 'Copied · clears in
60 s' and counts down; at zero the clipboard is cleared only if it still holds
the key (readText() where permitted — if the browser refuses to read, nothing
is wiped rather than risk eating something else). Any other copy made in the
app cancels the timer. No setting. Verified headless with a fake clock:
countdown ticks, clipboard emptied at 0; copying something else mid-countdown
cancels and leaves that content untouched.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/components/DeviceVerificationSetup.tsx

@@ -19,7 +19,7 @@ import { useSaveFile } from '../hooks/useSaveFile';
 import { useModalStyle } from '../hooks/useModalStyle';
 import { PasswordInput } from './password-input';
 import { ContainerColor } from '../styles/ContainerColor.css';
-import { copyToClipboard } from '../utils/dom';
+import { useSensitiveCopy } from '../hooks/useSensitiveCopy';
 import { AsyncStatus, useAsyncCallback } from '../hooks/useAsyncCallback';
 import { clearSecretStorageKeys } from '../../client/secretStorageKeys';
 import { ActionUIA, ActionUIAFlowsLoader } from './ActionUIA';
@@ -232,9 +232,8 @@ function RecoveryKeyDisplay({ recoveryKey }: RecoveryKeyDisplayProps) {
   const [show, setShow] = useState(false);
   const saveFile = useSaveFile();
 
-  const handleCopy = () => {
-    copyToClipboard(recoveryKey);
-  };
+  // [Gitea #156] The key leaves the clipboard again after 60 s, visibly.
+  const { copy: handleCopy, secondsLeft } = useSensitiveCopy(recoveryKey);
 
   const handleDownload = () => {
     const blob = new Blob([recoveryKey], {
@@ -272,8 +271,10 @@ function RecoveryKeyDisplay({ recoveryKey }: RecoveryKeyDisplayProps) {
         </Box>
       </Box>
       <Box direction="Column" gap="200">
-        <Button onClick={handleCopy}>
-          <Text size="B400">Copy</Text>
+        <Button onClick={handleCopy} aria-live="polite">
+          <Text size="B400">
+            {secondsLeft !== null ? `Copied · clears in ${secondsLeft} s` : 'Copy'}
+          </Text>
         </Button>
         <Button onClick={handleDownload} fill="Soft">
           <Text size="B400">Download</Text>

src/app/hooks/useSensitiveCopy.ts

@@ -0,0 +1,70 @@
+import { useCallback, useEffect, useRef, useState } from 'react';
+import { copyToClipboard } from '../utils/dom';
+
+export const SENSITIVE_COPY_TTL_S = 60;
+
+/**
+ * [Gitea #156] Copy a secret (recovery key) and clear it from the clipboard
+ * 60 s later — visibly: `secondsLeft` counts down for the button label. At
+ * zero the clipboard is cleared ONLY if it still holds our value
+ * (`readText()` where the browser allows it; when it doesn't, nothing is
+ * wiped — better to leave a key than to eat something else the user copied).
+ * Any other copy made in the app cancels the timer.
+ */
+export function useSensitiveCopy(value: string): {
+  copy: () => void;
+  secondsLeft: number | null;
+} {
+  const [secondsLeft, setSecondsLeft] = useState<number | null>(null);
+  const timer = useRef<number | undefined>(undefined);
+  const armed = useRef(false);
+
+  const cancel = useCallback(() => {
+    if (timer.current !== undefined) window.clearInterval(timer.current);
+    timer.current = undefined;
+    armed.current = false;
+    setSecondsLeft(null);
+  }, []);
+
+  useEffect(() => {
+    // Our own copy fires a `copy` event too; `armed` is set right after it.
+    const onCopy = () => {
+      if (armed.current) cancel();
+    };
+    document.addEventListener('copy', onCopy);
+    return () => {
+      document.removeEventListener('copy', onCopy);
+      cancel();
+    };
+  }, [cancel]);
+
+  const copy = useCallback(() => {
+    cancel();
+    copyToClipboard(value);
+    // Arm after this tick so the copy event of THIS copy doesn't cancel it.
+    window.setTimeout(() => {
+      armed.current = true;
+    }, 0);
+    let left = SENSITIVE_COPY_TTL_S;
+    setSecondsLeft(left);
+    timer.current = window.setInterval(() => {
+      left -= 1;
+      if (left > 0) {
+        setSecondsLeft(left);
+        return;
+      }
+      const clear = async () => {
+        try {
+          const current = await navigator.clipboard.readText();
+          if (current === value) await navigator.clipboard.writeText('');
+        } catch {
+          // read denied or unavailable — leave the clipboard alone
+        }
+      };
+      clear().catch(() => undefined);
+      cancel();
+    }, 1000);
+  }, [value, cancel]);
+
+  return { copy, secondsLeft };
+}