diff --git a/apps/app/tests/component/StageHeaderCell.test.ts b/apps/app/tests/component/StageHeaderCell.test.ts
new file mode 100644
index 00000000..096ea806
--- /dev/null
+++ b/apps/app/tests/component/StageHeaderCell.test.ts
@@ -0,0 +1,73 @@
+import { describe, expect, it } from 'vitest'
+import { mountWithVuexy } from '../utils/mountWithVuexy'
+import StageHeaderCell from '@/components/timetable/StageHeaderCell.vue'
+import type { Stage } from '@/types/timetable'
+
+/**
+ * jsdom-runnable assertions for the B2 + B3 prop seam:
+ *
+ *  - the explicit row-height-px prop applies as inline blockSize
+ *  - the prop's absence falls back to the legacy CSS path (no inline style)
+ *  - the conflict count badge appears only when > 0
+ *
+ * Visual proof of the freeze panes — sticky-left alignment, pixel-perfect
+ * stacking against StageRow — is jsdom-blind and lives on TEST-VISUAL-001.
+ */
+const stage: Stage = {
+  id: 's1',
+  event_id: 'ev1',
+  name: 'Hardstyle District',
+  color: '#e85d75',
+  capacity: 1000,
+  sort_order: 0,
+  created_at: null,
+  updated_at: null,
+}
+
+describe('StageHeaderCell — explicit row-height-px prop (B3 freeze-pane alignment)', () => {
+  it('applies blockSize inline when rowHeightPx prop is provided', () => {
+    const { wrapper } = mountWithVuexy(StageHeaderCell, {
+      props: { stage, rowHeightPx: 148 },
+    })
+
+    const root = wrapper.find('[data-stage-id="s1"]')
+
+    expect(root.attributes('style')).toMatch(/block-size:\s*148px/)
+  })
+
+  it('does not set blockSize inline when rowHeightPx is omitted (legacy CSS path)', () => {
+    const { wrapper } = mountWithVuexy(StageHeaderCell, {
+      props: { stage },
+    })
+
+    const root = wrapper.find('[data-stage-id="s1"]')
+    const style = root.attributes('style') ?? ''
+
+    expect(style).not.toMatch(/block-size/)
+  })
+
+  it('passes through laneCount=10 row height (484px) without truncation', () => {
+    const { wrapper } = mountWithVuexy(StageHeaderCell, {
+      props: { stage, rowHeightPx: 484 },
+    })
+
+    const root = wrapper.find('[data-stage-id="s1"]')
+
+    expect(root.attributes('style')).toMatch(/block-size:\s*484px/)
+  })
+
+  it('shows the conflict badge only when conflictCount > 0', () => {
+    const { wrapper: withZero } = mountWithVuexy(StageHeaderCell, {
+      props: { stage, conflictCount: 0 },
+    })
+
+    expect(withZero.find('.tt-stage-header__conflict').exists()).toBe(false)
+
+    const { wrapper: withTwo } = mountWithVuexy(StageHeaderCell, {
+      props: { stage, conflictCount: 2 },
+    })
+
+    expect(withTwo.find('.tt-stage-header__conflict').exists()).toBe(true)
+    expect(withTwo.find('.tt-stage-header__conflict').text()).toContain('2')
+  })
+})
diff --git a/apps/app/tests/unit/lib/timetable/row-height.test.ts b/apps/app/tests/unit/lib/timetable/row-height.test.ts
new file mode 100644
index 00000000..3f91acc1
--- /dev/null
+++ b/apps/app/tests/unit/lib/timetable/row-height.test.ts
@@ -0,0 +1,33 @@
+import { describe, expect, it } from 'vitest'
+import { computeStageRowHeight } from '@/lib/timetable/row-height'
+
+/**
+ * One-line helper, four assertion cases — keep this surface tight; this
+ * is the canonical row-height math for both StageRow content and the
+ * sticky-left StageHeaderCell. If either side drifts, the freeze panes
+ * misalign in the browser. The math:
+ *
+ *   max(1, laneCount) × (laneHeight + lanePad) + lanePad
+ *
+ * with the canonical constants laneHeight=44, lanePad=4 → 48 per lane + 4.
+ */
+const LANE_HEIGHT = 44
+const LANE_PAD = 4
+
+describe('computeStageRowHeight', () => {
+  it('falls back to single-lane height when laneCount is 0', () => {
+    expect(computeStageRowHeight(0, LANE_HEIGHT, LANE_PAD)).toBe(52)
+  })
+
+  it('returns 52px for laneCount=1', () => {
+    expect(computeStageRowHeight(1, LANE_HEIGHT, LANE_PAD)).toBe(52)
+  })
+
+  it('returns 148px for laneCount=3', () => {
+    expect(computeStageRowHeight(3, LANE_HEIGHT, LANE_PAD)).toBe(148)
+  })
+
+  it('returns 484px for laneCount=10 (10 × 48 + 4)', () => {
+    expect(computeStageRowHeight(10, LANE_HEIGHT, LANE_PAD)).toBe(484)
+  })
+})