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thymikeethymikee
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test(capture-kit): pin the ax1 digest wire format the daemon persists (#2941)
`computeAxDigest` returns a ~50-byte string that is persisted as post-action evidence and compared across daemon restarts (#1047), yet nothing in the suite pinned the bytes. Every test but two compared one invocation against another, so a change to the construction moved both sides and the file stayed green. Proven by mutant: deleting the NUL separators from `hashNode` — which makes the tuple ('ab', '', '') hash the same bytes as ('a', 'b', ''), i.e. two different trees reporting identical evidence — leaves `ax-digest.test.ts` at 9 passed. It is the only cross-field collision guard in the function and no test could see it go. Three additions, each with a named mutant: - field separation: ('ab','','') vs ('a','b','') vs ('a','','b') must differ. Separator removal now fails 2 tests. - fixed width: `ax1:` + exactly 16 hex, replacing the `startsWith('ax1:')` probe, which a widened `slice()` or a dropped prefix would survive. - a golden for a fixed 3-node set, so XOR width, separator placement, and the count folding are all contract. Narrowing `PER_NODE_HASH_BYTES` to 8 fails only this one. Test-only: no production line changes.
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‎packages/capture-kit/src/snapshot/__tests__/ax-digest.test.ts‎

Lines changed: 30 additions & 3 deletions
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@@ -61,10 +61,37 @@ test('digest for an empty node array is stable and reports zero nodes', () => {
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expect(result.digest).toBe(computeAxDigest([]).digest);
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});
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test('digest is prefixed for forward-compatible versioning', () => {
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const result = computeAxDigest([{ type: 'button', label: 'Continue' }]);
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test('digest separates the tuple fields so text shifted across them cannot collide', () => {
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// `hashNode` joins (type, label, identifier) through NUL separators. Drop them and
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// ('ab', '', '') hashes the same bytes as ('a', 'b', '') — two different trees that
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// would report identical evidence.
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const labelShifted = computeAxDigest([{ type: 'ab', label: '' }]);
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const labelSplit = computeAxDigest([{ type: 'a', label: 'b' }]);
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const identifierSplit = computeAxDigest([{ type: 'a', label: '', identifier: 'b' }]);
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expect(labelShifted.digest).not.toBe(labelSplit.digest);
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expect(labelShifted.digest).not.toBe(identifierSplit.digest);
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});
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test('digest is a versioned fixed-width hex string', () => {
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const { digest } = computeAxDigest([{ type: 'button', label: 'Continue' }]);
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expect(digest).toMatch(/^ax1:[0-9a-f]{16}$/);
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});
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test('golden: the ax1 wire format is pinned to these bytes', () => {
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// A digest is persisted as post-action evidence and compared across daemon restarts
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// (#1047), so the XOR width, separators, and count folding are all wire contract.
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const nodes = [
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{ type: 'button', label: 'Continue', identifier: 'continue-btn' },
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{ type: 'text', label: 'Welcome' },
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{ type: 'image', label: 'Logo' },
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];
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expect(result.digest.startsWith('ax1:')).toBe(true);
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expect(computeAxDigest(nodes)).toEqual({
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digest: 'ax1:0a88b2cbf989ae22',
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nodeCount: 3,
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});
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});
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test('digest ignores volatile fields such as rects that are not part of the tuple', () => {

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