Require nullable function result fields in native acceptance

[SaladDay]

The native pending-action acceptance rejected a successful tool result because the request omitted error, while the pinned resource schema requires error: null. Compare the resource’s required output and error fields with the request’s nullable values, preserving exact output contents and rejection of missing resource fields.

Validation: 24 focused runner/schema checks passed. Replaying the captured durable input and result fails the old assertion and passes the corrected assertion; missing error, changed output, and changed error remain rejected. No production behavior changes. The original live failure is retained, and the remaining live rounds still need qualification.

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