[Parity]: [P2] Pin the TDT routing-tail size law beyond 2-star saves

Imported from the engineering backlog (_bmad-output/implementation-artifacts/backlog.md, story tdt-export-routing-tail).
Priority P2 (do-first order) | Severity: med | Status: open | Epic: SimTower parity | Type: task | Recorded: 2026-07-08

Divergence from the 1994 original

Follow-up to the now-resolved tdt-trailing-structure-layout export half (v1.14.0). The exporter reaches the game's expected file length by emitting a FIXED-size 0xFF routing tail (TDT_ROUTING_TAIL_SIZE = 0x6400), validated for Classic towers up to 2★ (the only real saves on hand: empty TSTSAVE.TDT + a 2★ my_tower). The real game's trailing region is not a single fixed size across saves, so a much bigger 3★+ tower (more elevators/floors, sky lobbies, big crowds, cinemas/cathedral) could read past the fixed tail and 0x0799 again. Over-emitting is safe (the game ignores trailing slack); under-emitting is the crash. TODO once higher-star real saves are available: pin the tail SIZE as a function of tower content (or confirm a safe upper bound) and replace the fixed constant. Also refine the people census: our count is low (77 for a tower the game runs at ~291) because the IMPORT under-captures office/condo occupancy (see tdt-import-population-seed) and commercial customers aren't counted (see population-census-parity); the export faithfully mirrors whatever we import, so this rides those two items. NEEDS: a few 3★/4★ saves with varied transport (multiple/express/service elevators, escalators, sky lobbies, parking) to RE the tail-size law.

Read the _bmad-output/implementation-artifacts/backlog.md entry for tdt-export-routing-tail and inspect the exporter’s TDT_ROUTING_TAIL_SIZE handling. Start by obtaining varied 3★/4★ saves and comparing their trailing-region needs; done means replacing the fixed tail with a validated content-based law or safe upper bound without risking reads past the routing tail.