The flagged option now keeps its weight and takes part in normal draws.
It is still taken, without a draw, when constraints or weights leave
nothing to pick. Flagging an option never changes a normal pick, and a
fallback weighted 0 only ever stands in. Editors give it its normal
share and show a fallback chip beside it.
A wildcard option can be marked as the fallback. It never takes part in a
normal draw and is used only when constraints (an Only rule included), a
filter or zero weights leave nothing else to pick, instead of resolving to
an empty string. Works for top-level wildcards and nested @{} refs, and
emits an info-level `fallback_used` note in place of
`constraint_excludes_all_options`.
- engine: engine/modules/_fallback.py shared by the handler and
ref_option_pool; payload validation allows one boolean fallback on a
non-null option
- schema 9 (additive): FALLBACK_SCHEMA_VERSION stamped in TS and Python,
MAX_KNOWN_SCHEMA_VERSION 9, strict validator keeps the flag, parity
fixture regenerated
- library editor: "set as fallback" on an option's probability cell, a
fallback chip, its weight disabled and excluded from the shares
- canvas: FALLBACK badge on the option row, no share in probabilities
- WP Debug: "Fallback used" label and step fact
- docs, release note, CLAUDE.md
- bundle budget raised 420 -> 424 KB (maintainer approved)
Claude