T-330's guard keys on `scoring_mode` rather than on whether hierarchy data actually exists, so collapse is disabled for an HSJ config with NO hierarchy blocks — a dataset where collapse is provably safe.

[ms609]

Severity: P3 · Area: 11 (Collapse), 10 (HSJ/XFORM kernels)

Location: src/ts_rcpp.cpp:1829-1847 (ds.scoring_mode = HSJ set unconditionally at :1847); guards at src/ts_collapsed.cpp:24-25, :153-156

Verified REAL (haiku verifier): unpack_hsj sets the mode whenever hsjConfig is non-NULL, even with hierarchyBlocks empty, and both collapse guards then refuse on scoring_mode alone without checking whether hierarchy_blocks or sankoff_n_chars are populated. Cheap fix, and the predicate already exists: guard on !ds.hierarchy_blocks.empty() || ds.sankoff_n_chars > 0, which is what DataSet::topology_independent() uses. Cost of the current form is lost collapse (inflated n_topologies, fully-resolved output) on a degenerate-but-valid config, never a wrong score.

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Migrated 2026-08-04 from dev/red-team/findings.md; pre-tracker ID T-408. References to T-408 in source comments, dev/red-team/log.md, commit messages and PR bodies mean this issue — see dev/red-team/migration-map.tsv. Cross-repo references use the fully-qualified form agent-issues/TreeSearch#<n>; a bare #n means this repo.

[ms609]

Claiming — working on branch feature/hierarchy-guards, worktree TS-hierarchy-guards.