fusion/.changeset/fn-4717-worktrunk-resolver-surface.md

@runfusion/fusion

@runfusion/fusion
patch

Widen resolveWorktreeBackend to accept an optional binaryPathResolver, allow WorktrunkWorktreeBackend to be constructed with a lazy resolver in place of a literal path, and finalize the resolveWorktrunkBinary return contract (adds installed-release / installed-cargo source variants and an optional actionGateContext). Internal surface widening that unblocks FN-4681's binary-resolver wiring; no runtime behavior change for existing callers.