refactor(generator)!: drop IEnumerable member support

[OleRoss]

Summary

Lazy IEnumerable<T> members do not fit the separate sizing and writing API: counting can consume a sequence before serialization, and repeating a sequence can produce different data. No consumer needs this support. Reject these members, including declarations with BinaryElementCount, and keep arrays, memory, lists, and the four counted collection interfaces.

Stacked on #16; the base is codex/fix-floating-enum-collections.

Changes

• Report DBO009 with a materialization suggestion for IEnumerable<T> members. Ignored members remain allowed.
• Use Count directly for ICollection<T>, IReadOnlyCollection<T>, IList<T>, and IReadOnlyList<T>; sizing never enumerates.
• Delete the enum-enumerable helper, list writer wrappers, repeated utility selection, unused collection metadata, and runtime array/list shortcuts in interface writers. All retained interfaces share a bounded iteration path; primitive and enum elements reuse span writers. Generator source is roughly 380 lines smaller.
• Apply the same short-collection checks to primitives, enums, and objects. A declared count of two with one element now returns false instead of reporting unwritten bytes as successfully written. Surplus elements remain ignored for declared-count members.

Testing

• Windows, .NET 9 and .NET 10: all 211 runtime tests and 47 generator tests passed on each framework (516 executions total). Built with isolated outputs and ran the compiled xUnit test assemblies directly after the local dotnet test launcher failed.
• Verified both endian round trips through all four retained interfaces using non-array collections, member-defined boundaries and trailing fields, sizing without enumeration, one-pass writes, zero counts, exact iteration bounds, short-collection failure, and nested child failure progress.
• Snapshot tests verify rejection in Read, Write, and All modes, preservation of ignored enumerable members, and the simplified generated output.
• CSharpier and git diff --check passed. Independent local review found no remaining substantive issues.

Impact

Breaking source change: replace IEnumerable<T> declarations with supported collection types and explicitly materialize lazy sequences with ToArray() or ToList(). Writes below a declared or minimum count now consistently fail. Valid retained declarations keep their binary layout. Keep collections unchanged between sizing and writing and throughout serialization.

Checklist

• PR is scoped and not oversized
• Documentation (and changelog) is updated if needed
• CI Pipeline is successful
• Self-review was done

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-29T10:50:59.072806Z	9b6007c	PR opened

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