Expose retained request evidence version metadata
Saved requests retain source-version lineage, but product clients cannot discover those versions through a bounded authorized operation. Adds service-only invoker list_context_request_evidence_versions: up to50 deduplicated source/version IDs and provenance metadata per page, scoped to an owned request and current actor access.
The manifest distinguishes current projection from retained history and customer assertions from observations. Failed/candidate/creative-only outputs and withdrawn/removed inputs are withheld; a withdrawn dependency withholds the whole result. Cursors must be visible in the same request. No raw content, storage URLs, new tables, rights decisions, roster changes or provider calls. Original preview-applied migration is retained; forward correction inlines the bounded query and revokes direct helper access from service_role.
Validation:12 manifest cases plus the inherited release lifecycle case in each of two subclasses,14 executions total, pass on disposable PostgreSQL15/17. Initial regressions and direct-helper denial failed before fixes. Current abea720 refreshes released main and resolves the test-index conflict; fresh-head CI/preview/review are required. Earlier-head checks do not cover this head. No production migration or customer intake. Release database before API985 after specific approval.