Stale __current_case__ references in workflow_state._walker

Summary

_walker.py’s walk_native_state docstring claims it uses __current_case__ as a fallback for conditional branch selection, but the implementation (_select_which_when_native) never reads __current_case__ from state. Branch selection uses only the test parameter’s value + discriminator matching + default-when fallback. The docstring is vestigial from an earlier implementation.

What to clean up

_walker.py

1. Line 95 — docstring says "Handles: conditional branch selection (with __current_case__ fallback)". Remove the parenthetical; the function does test-value matching with default-when fallback, not __current_case__ index lookup.

2. Line 72 — __current_case__ in _NATIVE_BOOKKEEPING_KEYS. This is still correct to keep — the key does appear in native tool_state dicts written by the Galaxy server runtime (galaxy.tools.parameters.grouping populates it). The walker needs to tolerate it as a known bookkeeping key when check_unknown_keys=True. The issue is only with the docstring claiming it’s used for branch selection.

Other files (no code changes needed, docstring/comment only)

• clean.py:106 — docstring mentions __current_case__ as example bookkeeping key. Accurate, keep.
• stale_keys.py:4 — module docstring lists it as BOOKKEEPING category. Accurate, keep.
• roundtrip.py:300 — SKIP_KEYS set includes it for comparison skipping. Correct behavior, keep.

Context

The Galaxy server runtime (galaxy.tools.parameters.__init__, grouping.py, evaluation.py, etc.) actively writes and reads __current_case__ as an integer index into conditional.cases[]. This is a server-side implementation detail — the workflow_state validation module correctly avoids depending on it, selecting branches via the test parameter value and discriminator matching instead. The only issue is the stale docstring implying the old behavior persists.

Scope

Single docstring fix in _walker.py line 95. No behavioral changes.