Add the shared, uuid-keyed structural s-expr comparator (README §B) used by both
the live drift check (0003) and the round-trip tests (0004), plus a vitest setup.
- wasm/collab/sexpr-diff.ts: zero-dependency module (importable from standalone
app code and the Playwright specs). Tokenizes s-expr text into nested lists,
indexes item nodes by their direct (uuid "X") child, compares item sets order-
insensitively as multisets of normalized children, emitting
{ equal, added, removed, changed } with per-property a/b. ignoreTokens drops
volatile tokens. False-positive-free only for same-serializer inputs.
- wasm/collab/sexpr-diff.test.ts: 15 cases (parse, equality, changes, ignoreTokens).
- vitest config + test scripts (node env, isolated from the app build).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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