Wire CrowdThreading into three Oregon Trail catastrophes

#11 in Riparion/riparion-retro — merged 2026-06-09

Routes three Oregon Trail catastrophes through the shared CrowdThreading route-memory minigame instead of resolving them as instant stat hits.

Catastrophes wired in

• Hostile riders — Run (Mode::Flee): thread the breaks to lose the riders. Clear the route for a clean getaway (light scatter, +20 miles); foul it and they run you down into the existing QuickDraw gunfight.
• Rugged mountains (Mode::Climb): replaces the dead "never fires" quirk with a real ~30%/fortnight roll past mile 950, played as a line through the rocks. Miles lost graded by accuracy (clean ≈ −15, fouled ≈ −95), then falls through to the South Pass / Blue Mountains checks.
• Heavy fog (Mode::Fog): fix the trail before the fog (the map) closes. Hold the route → no time lost; lose your way → wander, scaled by drift.

Details

• New Mode::Flee/Climb/Fog, their thin CrowdThreading wrapper screens, and the crowd_threading kit feature.
• Each flow seeds its layout from existing game state (salted per game) so it stays deterministic for a save without perturbing the RNG stream.
• Bumps the oregon-trail crate to 0.1.2.

Tests

Engine tests for each flow (launch, clean vs fouled outcomes, fall-through, stale double-tap guards) plus harness arms. All 30 pass; clippy clean.

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