A venturi is a shelter's opposite — a gap between buildings SPEEDS the wind up
when it blows along the gap's axis. Where a tree shadow depends on being downwind
of the tree, a venturi depends on the wind being ALIGNED with a fixed axis the
SITE owns, so it fires only when the storm's direction swings to match: the
corner block is calm until the southerly comes through, then it screams. That
interplay is exactly SPRINT9's brief — funnel geometry is the site's, the wind
that funnels is the storm's.
Extends the existing shelter system rather than bolting on a parallel one:
speedAt/vecAt/verticalAt all route through one localHoriz, which now folds
venturiFactor in alongside spatialFactor and shelterFactor. The downdraft rides
local speed, so a funnelled wind gets a proportionally stronger downdraft for
free — physically right.
`setVenturi(list)` on the wind + router (A's "add it to the router too" rule; the
tripwire is green). Inert on an empty list, so backyard_01 is byte-identical —
asserted. Multiplier is ALWAYS ≥ 1 (a venturi accelerates, never shelters), and
it's C1-continuous through the change, so it can't snap a corner — both asserted
(aligned wind boosts 1.5×, crosswind exactly 1.0×, max frame jump 0.50 m/s).
Data lives in site JSON (A's schema, arriving with the extraction) — this is the
physics + the setter, ready to wire. Proposed shape flagged for A in THREADS.
Also fixed a stale comment: storm_02's _gusts_comment still said "HELD at 0.12
for now" from Sprint 3 while the value has been 0.45 since Sprint 4 — a lying
comment in a repo that reads comments as canon. Now records the real history and
the pending paired-0.40 flip.
Selftest 278/0/0; node 55/0/0.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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