Add fixture-only apparatus for representing multiple concurrent open
investigation items within a fixed case context.
New scenario 'multi-thread' exposes:
- A fixed central situation statement and case summary (product-launch
timing decision, drawn from existing pre-anchored-product-launch
data)
- Three open investigation items — none compulsory: enterprise customer
signing probability, competitor timing, financial viability comparison
- One engine recommendation (mt-ent-customer-signing, ordered first)
- User selection of any item; chosen item becomes visually primary while
others remain visible as context
- Experimental state isolated in _experimental / _experimentalState —
never aliases production graph fields
robbond