test(push): classify failing command substitution as legacy control

[LucaLin233]

Summary

Main run 34251584749, Debian Bash 5.2.37, reproduced trap unexpected EOF and exit 2 in command mode, round 1, delay 0. That control uses value=$(printf x); it is another command-substitution reproducer, not the pipeline replacement. The failure occurs before pipeline and batch tests.

Scope

Only tests/test-hup-parser.sh. Move command into the existing HUP_PARSER_INCLUDE_LEGACY opt-in group alongside process and snapshot. Retain its code and original red evidence. Default plain/pipeline modes retain all six delays, handler marker, exact exit 129, no-match status assertion, and hard per-case timeout. No production code, signal handler, lifecycle barrier or test runner changes.

Validation

Local bash -n and whitespace inspection passed; behavior tests run only in CI. Existing selector will run the changed parser suite in both environments. Full main and lint validations are tracked separately; a selective pass is not a full-suite claim.

Risks

This explicitly removes a newly demonstrated broken substitution control from the default passing gate, not a Bash fix. Legacy mode remains expected to expose failures and stops at the first failure. Does not establish a causal fix for deferred batch issue #53. Pipeline coverage is finite; no guaranteed immunity claim.

Rollback

Revert the eventual squash commit through a PR to restore default command coverage. No deployment or data migration. Merge requires explicit confirmation.

[LucaLin233]

Self-review completed against main dc58996. HEAD 45d83f6 changes only test mode classification/comments (+6/-5); no controller, assertions or production implementation change. Readback diff, whitespace and bash -n passed. CI 34252693792 passed Ubuntu and Debian: full=false, parser only, plain/pipeline six delays each, every exit 129 with handler marker required. Legacy command/process/snapshot code is retained, not rerun to green. No full-suite claim. Ready for user merge decision; main failure evidence remains retained.