test: drive the private key export screen end to end (closes #253)

The Chrome suite now drives the private key export screen as it drives the
recovery phrase screen: the correct password shows the key, leaving by the
settings gear empties the screen, and leaving while the password is still
being checked never puts the key on it. The cases use the imported key
wallet: leaving drops the address the screen was showing, so on an HD
wallet a late decrypt fails by itself and the liveness check would go
untested. Only the phrase screen's state reader now takes the screen's
name, and serves both; the wipe assertion takes the secret, as before. A
second open in one popup session throws (#460), so the cases reopen the
popup before it.

Model: opus-5-5

TODO.md

@@ -45,6 +45,18 @@ but the review is broader than any of them.
 
 # Completed Steps
 
+- 2026-10-05: The Chrome end-to-end suite drives the private key export screen
+  as it drives the recovery phrase screen
+  ([#253](https://git.eeqj.de/sneak/AutistMask/issues/253)): the correct
+  password shows the key, leaving by the settings gear empties the screen, and
+  leaving while the password is still being checked never puts the key on it.
+  The cases use the imported key wallet rather than the HD one. Leaving drops
+  the address the screen was showing, and an HD wallet's key cannot be derived
+  without it, so on an HD wallet a late decrypt fails by itself and would never
+  exercise the check that discards it. The screen cannot yet be opened twice in
+  one popup session ([#460](https://git.eeqj.de/sneak/AutistMask/issues/460)),
+  so the cases reopen the popup before the second open.
+
 - 2026-10-05: The StateRecovery screen is driven in a real browser under the
   shipped CSP, in both end-to-end suites
   ([#361](https://git.eeqj.de/sneak/AutistMask/issues/361)). A stored record