The seeded initialPlan lived in modalManager state while embedded Planning
fully unmounts on main-content navigation, wiping its in-component auto-start
guard — so every navigate-back remount (and the project-switch remount key)
auto-started a duplicate planning session and abandoned the one in flight.
The payload is now a one-shot handoff: PlanningModeModal calls the new
onInitialPlanConsumed the moment auto-start fires, useModalManager clears
planningInitialPlan, and remounts take the stored-active-session restore path.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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