test(clap): cover stateful parser features

[jdx]

Replaces #1149, which GitHub automatically marked merged when dependent branch refs temporarily matched during a restack. This is the same layer on the corrected stack.\n\n_This pull request was generated by Codex._

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Note

Low Risk
Test-only and plan-status updates; no parser or production behavior changes.

Overview
Extends the clap micro-conformance harness with four more paired CLIs so usage and clap agree on default-missing values, flatten + skip, required trailing --, and short vs long version output.

PLAN.md now lists those rows as covered; remaining matrix rows are still open.

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