Enables dry-run checking before committing to case adoption. The preflight
shares the same side-effect-free checks (steps 1–3) as the real take-ownership
handler, so it cannot drift from what will actually succeed. Returns the same
status codes and error shapes as the real endpoint (200 with wouldSucceed:true,
or 409/404/422 if it would fail).
Portal renders a "Vooraf controleren" button for legacy cases, surfaced through
the existing actions block pattern. Confirmed in smoke.sh with two cases: one
where preflight predicts success (and writes nothing), one where it predicts
a named invariant failure (matching what the real call reproduces).
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
ehoandClaude Haiku 4.5
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