[Bug]: iOS 2.2.0 shows no Build/Plan control or Implement action with Labs → Legacy → Plan Mode on #32295

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/mobile

Steps to reproduce

1. On iOS, open Settings → Labs → Legacy and turn on Plan Mode.
2. Start a new thread on a Claude model (tested with the built-in Claude Opus 5.5 and a custom claudeAgent instance).
3. Look for the Build/Plan control in the composer and in Thread settings.
4. Open a thread whose plan finished on desktop/web, and look for the Implement action.

Expected behavior

With Plan Mode on, mobile shows the Build/Plan control as web does, and a finished plan offers
"Implement" / "Implement in a new thread".

Actual behavior

• No Build/Plan control. Thread settings → Options shows only Reasoning / Ultracode / Fast Mode / Runtime, and the composer has no mode control.
• Threads started from mobile are stored as interaction_mode = default.
• No Implement action after a plan finishes, so a mobile-only user cannot move a plan into implementation.
• The server reports showInteractionModeToggle: true for the claudeAgent driver, including custom instances, and
  interaction_mode = plan threads created from desktop on the same instances work. The gap appears to be mobile-only.

Impact

Major degradation or frequent failure

Version or commit

iOS app 2.2.0; server t3 serve 0.1.8-nightly.20261106.4262

Environment

iPhone (iOS), also seen on iPad; Linux arm64 host reached through the managed relay