test(crypto): add round-trip tests for Unicode and binary edge cases …

[Anadudev]

Closes #1722

Proposed Changes

Unicode & Binary Round-Trip Tests (tests/unit/crypto/envelope-roundtrip.test.ts)

• Added comprehensive round-trip tests verifying sealEnvelope -> openEnvelope behavior across diverse text encodings:
  • Multilingual Scripts: Tested Arabic, Hebrew, CJK, Devanagari, Cyrillic, and Greek scripts.
  • Emoji & ZWJ Sequences: Tested family emoji (👨‍👩‍👧‍👦), skin tone modifiers (👍🏽), flags, and variation selectors (\uFE0F).
  • Code Point Exactness: Asserted exact code point array matching (toCodePoints(opened.body) === toCodePoints(input)).
  • Combining Characters & Normalization Separation: Verified that NFC (é, U+00E9) and NFD (e + \u0301, U+0065 U+0301) retain their distinct code point sequences and produce distinct content commitments without silent normalization.
  • Null Bytes & Control Characters: Tested strings containing embedded null bytes (\u0000) and ASCII control characters (\u0007, \u001B).
  • Canonicalization Independence: Confirmed canonicalizePayload and canonicalizeJcs preserve exact string code points while sorting JSON keys deterministically.
  • Boundary Payloads & Attachments: Tested large 1MB multi-byte payloads and Unicode attachment filenames (📄_测试_отчёт_2026.pdf).

Verification Plan

Automated Tests

• Executed node node_modules/vitest/vitest.mjs run tests/unit/crypto/envelope-roundtrip.test.ts: 11 passed (11).
• Executed node node_modules/vitest/vitest.mjs run tests/unit/crypto: 26 test files passed, 240/240 tests passed.
• Executed npx eslint tests/unit/crypto/envelope-roundtrip.test.ts: 0 lint errors.