Disable pi thinking for DeskTalk agent sessions

[Copilot]

DeskTalk’s pi agent wiring was allowing session thinking/reasoning to remain enabled, which slows interactive use. This change forces DeskTalk-managed pi sessions to run with thinking disabled across session creation, restore, and provider/model sync.

• Session defaults

  • Introduce DeskTalk-specific session handling that forces pi session thinking level to off.
  • Apply this consistently for newly created sessions and reopened sessions.

• Preference sync behavior

  • Reapply off after provider/model synchronization so model switches do not re-enable reasoning.

• Coverage

  • Add focused unit coverage around preference sync to ensure thinking stays disabled when the active model changes.

if (
  !this.session.model ||
  this.session.model.provider !== targetModel.provider ||
  this.session.model.id !== targetModel.id
) {
  await this.session.setModel(targetModel);
}

disableSessionThinking(this.session);