Paid tier only. Calling this without an authenticated CivilQuants account returns TIER_INSUFFICIENT — sign up at https://civilquants.com/pricing or use the free-tier alternative compute_cantilever_wall. Modular gabion retaining wall built from welded or hexagonal-mesh wire baskets filled with hard angular graded stone (SHW Cl. 622). The first non-concrete retaining structure in the platform and the FIRST member of the earth_structures L1 leaf — opening Phase E. Spans four structural forms via the gabion_form discriminator: STACKED_RECTANGULAR (standard highway boundary), STACKED_STEPPED (architectural / heritage), BATTERED (tall walls with back batter), and FACING_MATTRESS (Reno-type mattresses for slope facing / scour protection). Eight variant presets exercise the parameter form covering all four gabion_form values: highway boundary, landscape, stepped front, heritage stepped, battered, river training, scour apron, and tall battered. Routes via three new WorkCategory entries (GABION_BASKET, GABION_FACING_MATTRESS, STONE_FILL) — the first session where the classed-then-legacy discriminator pattern is applied to fundamentally new measurement vocabulary rather than to existing concrete categories. Codes: CESMM4 E.8.1-3 (Class E — Earthworks), NRM2 5.20-22 (Group 5 — Excavating and filling), MMHW 600.12-14 (Series 600 — Earthworks; SHW Cl. 622/623), and SMM7 D41.1/D41.2/D20.20 (D41 — Crib walls / gabions / reinforced earth — the only standard with a NAMED home). 16th use of the discriminator pattern, first applied to new WorkCategories rather than legacy ones. Example params: wall_height=3 m (0.1–8), wall_length=25 m (5–200), basket_length_m=2 m (1–3). Example call: {"params": {"wall_height": 3, "wall_length": 25, "basket_length_m": 2}, "standard": "MMHW"}. Omitted parameters use sensible engineering defaults. Pass deliverables=["xlsx","dxf","pdf"] (any subset) to also receive one-shot download URLs in the same call: Excel BoQ (both tiers, watermarked free) plus the dimensioned DXF (CAD) and PDF drawing sheets (paid tier).