feat(equipment): pure overlap/eligibility logic + Zod schemas

equipment-logic.ts: half-open intervalsOverlap, hasConflict (only
reserved rows block), reservationEligibility (status/active gate, future
window, no-overlap, required-cert with manager override). Dependency-free,
9 unit tests (suite 382 -> 391). validations.ts: equipment/reservation
schemas; reserve carries an optional manager-only memberId.

__tests__/equipment-logic.test.ts

@@ -0,0 +1,63 @@
+import { describe, it, expect } from 'vitest'
+import {
+  intervalsOverlap,
+  hasConflict,
+  reservationEligibility,
+} from '@/lib/equipment-logic'
+
+describe('intervalsOverlap', () => {
+  it('detects overlap and treats touching as non-overlap', () => {
+    expect(intervalsOverlap('2026-01-01T10:00Z', '2026-01-01T12:00Z', '2026-01-01T11:00Z', '2026-01-01T13:00Z')).toBe(true)
+    expect(intervalsOverlap('2026-01-01T10:00Z', '2026-01-01T12:00Z', '2026-01-01T12:00Z', '2026-01-01T13:00Z')).toBe(false)
+    expect(intervalsOverlap('2026-01-01T10:00Z', '2026-01-01T12:00Z', '2026-01-01T08:00Z', '2026-01-01T09:00Z')).toBe(false)
+  })
+  it('is false on unparseable input', () => {
+    expect(intervalsOverlap('x', 'y', 'a', 'b')).toBe(false)
+  })
+})
+
+describe('hasConflict', () => {
+  const req = ['2026-02-01T10:00Z', '2026-02-01T12:00Z'] as const
+  it('only reserved rows block', () => {
+    expect(hasConflict(req[0], req[1], [{ starts_at: '2026-02-01T11:00Z', ends_at: '2026-02-01T13:00Z', status: 'reserved' }])).toBe(true)
+    expect(hasConflict(req[0], req[1], [{ starts_at: '2026-02-01T11:00Z', ends_at: '2026-02-01T13:00Z', status: 'cancelled' }])).toBe(false)
+    expect(hasConflict(req[0], req[1], [{ starts_at: '2026-02-01T11:00Z', ends_at: '2026-02-01T13:00Z', status: 'completed' }])).toBe(false)
+  })
+  it('no conflict when disjoint', () => {
+    expect(hasConflict(req[0], req[1], [{ starts_at: '2026-02-01T12:00Z', ends_at: '2026-02-01T14:00Z', status: 'reserved' }])).toBe(false)
+  })
+})
+
+describe('reservationEligibility', () => {
+  const base = {
+    equipmentStatus: 'available',
+    equipmentActive: true,
+    startsAt: '2026-06-01T10:00:00Z',
+    endsAt: '2026-06-01T12:00:00Z',
+    now: '2026-05-16T00:00:00Z',
+    conflict: false,
+    requiresCert: false,
+    memberHasCert: false,
+    managerOverride: false,
+  }
+  it('allows a clean future reservation', () => {
+    expect(reservationEligibility(base).ok).toBe(true)
+  })
+  it('blocks archived/retired/maintenance', () => {
+    expect(reservationEligibility({ ...base, equipmentActive: false }).ok).toBe(false)
+    expect(reservationEligibility({ ...base, equipmentStatus: 'retired' }).ok).toBe(false)
+    expect(reservationEligibility({ ...base, equipmentStatus: 'maintenance' }).ok).toBe(false)
+  })
+  it('blocks past start and end<=start', () => {
+    expect(reservationEligibility({ ...base, startsAt: '2026-05-01T10:00:00Z' }).ok).toBe(false)
+    expect(reservationEligibility({ ...base, endsAt: '2026-06-01T10:00:00Z' }).ok).toBe(false)
+  })
+  it('blocks on conflict', () => {
+    expect(reservationEligibility({ ...base, conflict: true }).ok).toBe(false)
+  })
+  it('enforces the cert gate with manager override', () => {
+    expect(reservationEligibility({ ...base, requiresCert: true, memberHasCert: false }).ok).toBe(false)
+    expect(reservationEligibility({ ...base, requiresCert: true, memberHasCert: true }).ok).toBe(true)
+    expect(reservationEligibility({ ...base, requiresCert: true, memberHasCert: false, managerOverride: true }).ok).toBe(true)
+  })
+})