A code-coverage pass found two source files at 0% in the standing suite (covered
only by opt-in gates) and one large under-covered file:
- XSDParserUnion.swift (Document(composing:), the multi-document union, #161) was
exercised only by the opt-in XSTS harness, so plain `swift test` never ran
multi-document composition. SchemaComposingTests now covers it via a
cross-document substitution group (0% to 92% line).
- XSLTCollation.swift (language-tailored xsl:sort orders) was unexercised by any
standing test. XSLTCollationTests covers the Polish/Russian tables and the
fallback (0% to 88% line).
- StreamingDecoder.swift (byte-at-a-time CJK/UTF decode) had the streaming/split
path under-tested. StreamingDecoderTests feeds bytes one at a time through GBK,
Big5, Shift_JIS, EUC-KR, EUC-JP, GB18030, the UTF-16/32 BOM paths, and a
malformed sequence (48% to 80% line, 37% to 72% region). Expected scalars were
taken from the decoder and pinned.
Test-only; +10 tests; full suite green (1568).
