fix: refuse a comma in a name only where the serializer does

[Reefact]

Summary

EMN0004 reported a comma inside a declared name on every enum, and the start-up check refused one, on the reading that a comma separates values everywhere so a name carrying one can never be read back. Measured against the serializer, that is false off [Flags] — and the binder did worse than refuse the shape: once past the check it read "a,b" as a | b, a different member, silently.

What System.Text.Json actually does

Measured, not read off a specification:

enum	value	result
ordinary, declaring a, b and a,b	"a,b"	Ab — the whole name wins over the split
ordinary, same enum	"a, b"	a | b — no name is spelled with that space
ordinary, declaring news,world	write / read	"news,world" round-trips
[Flags], declaring "read,write"	first use	InvalidOperationException: "Flags enums must additionally not contain commas"

So the serializer looks the trimmed value up as one name before it splits anything, and refuses a comma inside a name on [Flags] alone. Refusing it everywhere made a registered enum stricter than the same enum left alone — which EnumContract's own remarks call the one thing this package promises never to do.

Type of change

• Bug fix
• New feature
• Breaking change to the public API
• Refactoring
• Analyzer / diagnostic change
• Tests
• Documentation
• Build / CI / tooling

Changes

• EnumContract.TryParse looks the whole trimmed value up as a name before splitting, and splits only when that misses. The reorder cannot change any contract that was legal before, since none of them could contain a comma — and the suite agrees: only the three tests pinning the old decision failed.
• MalformedNameProblem takes isFlags; the comma test is the one that reads it, because it is the one the serializer scopes that way. Problem.CommaInName → CommaInFlagsName, message reworded.
• EnumContractAnalyzer resolves System.FlagsAttribute at compilation start and reports EMN0004 only on an enum carrying it. CommaInName → CommaInFlagsName. Title, message and description in Resources.resx all say what the rule is scoped to.
• Parity fixtures rather than flipped assertions: CommaInsideAName (a, b, a,b) and CommaBesideCsharpNames join ReadParityTests, whose derived corpus compares every casing and every ordered pair against the serializer; CommaInsideAName joins FormattingParityTests. Reverting TryParse fails both with the divergence spelled out — 'a,b': System.Text.Json reads 4, this library reads 3.
• Topic joins the OpenAPI host, where the name reaches the published closed list: the document advertises news,world, the server binds it as one value, and news, world is refused — so the two readings are held apart rather than assumed distinct.
• Analyzer tests: EMN0004 stays silent on an ordinary enum, still fires on a [Flags] one whose other members are ordinary, and its message names [Flags].
• Docs: EMN0004.en/fr.md rewritten (the "Why it matters" section was two false sentences), both index tables, the EMN0002 cross-reference, and a paragraph in contract-rules.en/fr.md stating the whole-name-first order. The [Unreleased] changelog entry celebrating the widening is replaced by one describing the correction, in both languages — nothing had shipped, so leaving the pair would only contradict itself.

Testing

• dotnet build -c Release — clean, warnings are errors here
• dotnet test -c Release — 923 passed, 0 failed
• tests/PackageSmokeTest/run.sh — run because the analyzers changed; "The published package behaves as documented."

Also run: tools/style/lint-layout.sh (nothing to report), and the parity fixtures against the previous TryParse, to confirm they fail without the fix.

Public API

• No change to the public surface
• The surface changed and the baseline was updated in the same commit

The renamed descriptor is on the analyzers assembly, which carries no baseline; both packable projects are untouched.

Documentation

• README / docs/ updated
• The French counterpart was updated to match
• CHANGELOG.md and docs/for-users/CHANGELOG.fr.md both updated
• No documentation change required

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https://claude.ai/code/session_01M5U2BZXpHQr7YcfNHVx9dA

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