Align the developer-message fix with the Provider API transport router.
The fix stays scoped to the legacy /alpha/generate converter, and the
OMP advisory compat test now forces the upgrade_required fallback so the
advisory is asserted on the generate request body.
Add a fixture extension that injects an advisor-style custom message
on session start, and assert the advisory XML reaches params.messages
verbatim, in chronological position, and is not hoisted into
params.system.
Port the models phase to `omp models --json`. `--list-models` no
longer exists in current OMP (verified on 17.3.5), so the phase
failed before reaching print mode.
warc0s