diff --git a/common/src/util/array.test.ts b/common/src/util/array.test.ts
new file mode 100644
index 0000000000..3cf99f58ad
--- /dev/null
+++ b/common/src/util/array.test.ts
@@ -0,0 +1,238 @@
+import { describe, test, expect } from 'bun:test'
+
+import { filterDefined, buildArray, groupConsecutive } from './array'
+
+describe('filterDefined', () => {
+  test('removes null and undefined values from array', () => {
+    const input = [1, null, 2, undefined, 3]
+    const result = filterDefined(input)
+    expect(result).toEqual([1, 2, 3])
+  })
+
+  test('preserves falsy values that are not null or undefined', () => {
+    const input = [0, false, '', null, undefined, 'hello']
+    const result = filterDefined(input)
+    expect(result).toEqual([0, false, '', 'hello'])
+  })
+
+  test('returns empty array when all values are null or undefined', () => {
+    const input = [null, undefined, null]
+    const result = filterDefined(input)
+    expect(result).toEqual([])
+  })
+
+  test('returns empty array for empty input', () => {
+    const input: number[] = []
+    const result = filterDefined(input)
+    expect(result).toEqual([])
+  })
+
+  test('preserves array for values with no null or undefined', () => {
+    const input = [1, 2, 3, 4, 5]
+    const result = filterDefined(input)
+    expect(result).toEqual([1, 2, 3, 4, 5])
+  })
+
+  test('works with object arrays', () => {
+    const input: (string | null | undefined)[] = ['a', null, 'b', undefined]
+    const result = filterDefined(input)
+    expect(result).toEqual(['a', 'b'])
+  })
+})
+
+describe('buildArray', () => {
+  test('flattens nested arrays', () => {
+    const result = buildArray(1, [2, 3], [[4, 5]])
+    expect(result).toEqual([1, 2, 3, 4, 5])
+  })
+
+  test('removes falsy values', () => {
+    const result = buildArray(1, null, 2, undefined, 3, false, 0, '')
+    expect(result).toEqual([1, 2, 3])
+  })
+
+  test('handles deeply nested arrays', () => {
+    const result = buildArray([[[1, 2], [3, 4]], [[5, 6]]])
+    expect(result).toEqual([1, 2, 3, 4, 5, 6])
+  })
+
+  test('returns empty array when all values are falsy', () => {
+    const result = buildArray(null, undefined, false, 0, '')
+    expect(result).toEqual([])
+  })
+
+  test('returns empty array with no arguments', () => {
+    const result = buildArray()
+    expect(result).toEqual([])
+  })
+
+  test('works with single value', () => {
+    const result = buildArray(42)
+    expect(result).toEqual([42])
+  })
+
+  test('handles mixed nested and flat values', () => {
+    const result = buildArray(1, [2, 3], 4, [5, [6, 7]], 8)
+    expect(result).toEqual([1, 2, 3, 4, 5, 6, 7, 8])
+  })
+
+  test('preserves string values', () => {
+    const result = buildArray('a', ['b', 'c'], [['d']])
+    expect(result).toEqual(['a', 'b', 'c', 'd'])
+  })
+
+  test('removes only falsy values and preserves other values', () => {
+    const result = buildArray([1, null, 2], undefined, [false, 3, 0])
+    expect(result).toEqual([1, 2, 3])
+  })
+
+  test('preserves objects that are truthy', () => {
+    const obj1 = { a: 1 }
+    const obj2 = { b: 2 }
+    const result = buildArray(obj1, [obj2])
+    expect(result).toEqual([obj1, obj2])
+  })
+})
+
+describe('groupConsecutive', () => {
+  test('groups consecutive items with same key', () => {
+    const input = [1, 1, 2, 2, 2, 3, 1]
+    const result = groupConsecutive(input, (x) => x)
+    expect(result).toEqual([
+      { key: 1, items: [1, 1] },
+      { key: 2, items: [2, 2, 2] },
+      { key: 3, items: [3] },
+      { key: 1, items: [1] },
+    ])
+  })
+
+  test('handles empty array', () => {
+    const result = groupConsecutive([], (x) => x)
+    expect(result).toEqual([])
+  })
+
+  test('handles single item', () => {
+    const result = groupConsecutive([42], (x) => x)
+    expect(result).toEqual([{ key: 42, items: [42] }])
+  })
+
+  test('handles all items with different keys', () => {
+    const input = [1, 2, 3, 4, 5]
+    const result = groupConsecutive(input, (x) => x)
+    expect(result).toEqual([
+      { key: 1, items: [1] },
+      { key: 2, items: [2] },
+      { key: 3, items: [3] },
+      { key: 4, items: [4] },
+      { key: 5, items: [5] },
+    ])
+  })
+
+  test('handles all items with same key', () => {
+    const input = [1, 1, 1, 1]
+    const result = groupConsecutive(input, (x) => x)
+    expect(result).toEqual([{ key: 1, items: [1, 1, 1, 1] }])
+  })
+
+  test('works with object keys', () => {
+    const input = [
+      { type: 'a', value: 1 },
+      { type: 'a', value: 2 },
+      { type: 'b', value: 3 },
+    ]
+    const result = groupConsecutive(input, (x) => x.type)
+    expect(result).toEqual([
+      {
+        key: 'a',
+        items: [
+          { type: 'a', value: 1 },
+          { type: 'a', value: 2 },
+        ],
+      },
+      {
+        key: 'b',
+        items: [{ type: 'b', value: 3 }],
+      },
+    ])
+  })
+
+  test('groups by complex key function', () => {
+    const input = ['apple', 'apricot', 'banana', 'blueberry']
+    const result = groupConsecutive(input, (s) => s[0]) // Group by first letter
+    expect(result).toEqual([
+      { key: 'a', items: ['apple', 'apricot'] },
+      { key: 'b', items: ['banana', 'blueberry'] },
+    ])
+  })
+
+  test('works with numeric keys', () => {
+    const input = [1, 2, 1, 3, 3, 2]
+    const result = groupConsecutive(input, (x) => x % 2) // Group by odd/even
+    expect(result).toEqual([
+      { key: 1, items: [1] },
+      { key: 0, items: [2] },
+      { key: 1, items: [1, 3, 3] },
+      { key: 0, items: [2] },
+    ])
+  })
+
+  test('groups objects with complex keys', () => {
+    const input = [
+      { id: 1, status: 'active' },
+      { id: 2, status: 'active' },
+      { id: 3, status: 'inactive' },
+      { id: 4, status: 'active' },
+    ]
+    const result = groupConsecutive(input, (x) => x.status)
+    expect(result).toEqual([
+      {
+        key: 'active',
+        items: [
+          { id: 1, status: 'active' },
+          { id: 2, status: 'active' },
+        ],
+      },
+      {
+        key: 'inactive',
+        items: [{ id: 3, status: 'inactive' }],
+      },
+      {
+        key: 'active',
+        items: [{ id: 4, status: 'active' }],
+      },
+    ])
+  })
+
+  test('handles string comparison correctly', () => {
+    const input = ['a', 'a', 'b', 'b', 'a']
+    const result = groupConsecutive(input, (x) => x)
+    expect(result).toEqual([
+      { key: 'a', items: ['a', 'a'] },
+      { key: 'b', items: ['b', 'b'] },
+      { key: 'a', items: ['a'] },
+    ])
+  })
+
+  test('works with null and undefined values', () => {
+    const input = [null, null, 'a', 'a', undefined]
+    const result = groupConsecutive(input, (x) => x)
+    expect(result).toEqual([
+      { key: null, items: [null, null] },
+      { key: 'a', items: ['a', 'a'] },
+      { key: undefined, items: [undefined] },
+    ])
+  })
+
+  test('handles objects with deep equality', () => {
+    const input = [
+      { nested: { value: 1 } },
+      { nested: { value: 1 } },
+      { nested: { value: 2 } },
+    ]
+    const result = groupConsecutive(input, (x) => x.nested)
+    // Since isEqual does deep comparison, same nested object structure should group
+    expect(result.length).toBe(2)
+    expect(result[0].items.length).toBe(2)
+    expect(result[1].items.length).toBe(1)
+  })
+})
diff --git a/common/src/util/array.ts b/common/src/util/array.ts
index 44ac05dc29..e0c7efe6c1 100644
--- a/common/src/util/array.ts
+++ b/common/src/util/array.ts
@@ -15,8 +15,9 @@ export function groupConsecutive<T, U>(xs: T[], key: (x: T) => U) {
   if (!xs.length) {
     return []
   }
-  const result: any[] = []
-  let curr = { key: key(xs[0]), items: [xs[0]] }
+  type Group = { key: U; items: T[] }
+  const result: Group[] = []
+  let curr: Group = { key: key(xs[0]), items: [xs[0]] }
   for (const x of xs.slice(1)) {
     const k = key(x)
     if (!isEqual(k, curr.key)) {