* fix(core): roadmap upgrade must not process.exit inside the no-throw hub (#1538)
The upgrade handler called process.stderr.write + process.exit(1) on an
unsupported --convention, structurally bypassing the command-routing-hub's
no-throw contract (ADR-0012). It also parsed only the space-separated
--convention <value> form, so --convention=<value> was silently dropped and
defaulted to milestone-prefixed, running the migration the user did not request.
Throw instead of exit (the hub converts to HandlerFailure and the adapter routes
it through error()); parse both --convention forms and fail closed on any
missing/unsupported value.
Claude-Session: https://claude.ai/code/session_01R88n7Q54bAaVHFkDbbH1yz
* chore(changeset): Fixed fragment for #1539 (roadmap upgrade hub contract)
Claude-Session: https://claude.ai/code/session_01R88n7Q54bAaVHFkDbbH1yz
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Co-authored-by: Tom Boucher <trekkie@nomorestars.com>
