Companion to the import fix: a clause whose version segment does not parse
(`>=0.21.1,<0.x`) must fail admission rather than silently gate nothing.
Salvage note: the source hunk (same import fix) and the duplicate positive
test from PR #108842 were dropped in favour of the earlier #107553; only the
negative test is carried here.
538+570+296+216 lines of change-detectors → 4 files of contract tests:
seed catalog valid, bad entries skipped, kill list name-or-repo, live
fallback+union; real-git pinned install + sidecar + re-pin; kill list
blocks CLI/dashboard/TUI with only the CLI bypass; dashboard merge via
sidecar; probe get_config default; extractor live document.
