fix: avoid colliding with the next task when the gap is too small

The min-spacing fallback spread from the lower bound and could hand a
batch item the exact position of the following task, which the api's
conflict repair then scatters. Address pr-swarm finding.

frontend/src/helpers/calculateItemPosition.ts

@@ -60,9 +60,9 @@ export const calculateItemPositions = (
 	const spacing = (positionAfter - base) / (count + 1)
 
 	// The gap is too small to subdivide without the values colliding after the JSON
-	// round-trip. Give up on staying inside it and only keep the batch itself ordered.
+	// round-trip. Spread past positionAfter on purpose so the batch doesn't collide with it.
 	if (spacing < MIN_POSITION_SPACING) {
-		return spread(base, MIN_POSITION_SPACING)
+		return spread(Math.max(base, positionAfter), MIN_POSITION_SPACING)
 	}
 
 	return spread(base, spacing)

frontend/src/helpers/calculateTaskPosition.test.ts

@@ -82,6 +82,13 @@ describe('calculateItemPositions', () => {
 		expect(positions).toEqual([...positions].sort((a, b) => a - b))
 	})
 
+	it('should not collide with the following item when there is nothing before and the gap is too small', () => {
+		const positions = calculateItemPositions(7, null, 0.05)
+		expect(positions).not.toContain(0.05)
+		expect(new Set(positions).size).toBe(7)
+		expect(positions).toEqual([...positions].sort((a, b) => a - b))
+	})
+
 	it('should keep distinct positions after a JSON round-trip', () => {
 		const positions = calculateItemPositions(10, null, 1)
 		const deserialized = JSON.parse(JSON.stringify(positions))