[Parity]: [P3] Does 1994 commercial ever go vacant? (TDT vacancy round-trip, harness-gated)

Imported from the engineering backlog (_bmad-output/implementation-artifacts/backlog.md, story tdt-commercial-vacancy-roundtrip).
Priority P3 (do-first order) | Severity: low | Status: idea | Epic: SimTower parity | Type: design-decision | Recorded: 2026-07-12

Divergence from the 1994 original

Party decision 2026-07-12 (PR #184 takeover review): harness-gated. TDT import seeds every non-construction fastFood/restaurant/shop as occupied and ignores the unit status byte; our exporter never writes a status for commercial. So vacancy cannot round-trip: export a vacant venue, reimport, it comes back occupied and the next export adds its catalog customers (self-round-trip census drift). Cloud's read: the 1994 game likely has no vacant-commercial state at all (built venues always operate), which would make the importer FAITHFUL and the drift a Modern-tower-only lossy edge. Validate against the real game via the Wine harness (does the 1994 status byte ever encode commercial vacancy?) before touching the exporter/importer; if canon has no vacancy, document the one-way mapping in the fidelity report instead.

Start with the referenced backlog story, tdt-commercial-vacancy-roundtrip, and inspect the importer/exporter behavior described for commercial status. Use the Wine harness to determine whether the 1994 game encodes commercial vacancy; done means either validating the round-trip behavior and updating the fidelity report, or identifying the exporter/importer change required by the result.