Export one workflow run as a sealed XMD artifact

[taras]

Delivered baseline

Closed by PR #615 at 0962ea2d69abab66c5ad39ea06ea931ae0a93f8a as part of #599.

This issue delivered the existing WorkflowLifecycle.export, lock-held committed-frontier detachment, authenticated root/component definition closure, recovery-copy discipline, V1 sealing, xmd workflow export, no-clobber staging/publication, and XE1–XE7/WXP1–WXP6 regressions.

The retained transaction and lifecycle contracts are:

• The executor lock owns selection and detachment of one committed source frontier.
• Definition retrieval/authentication and artifact writing occur after run-owned values are detached and the source lock is released.
• The source run is never repaired, settled, replayed, appended to, or relabelled.
• Fallible pre-publication cleanup finishes before the synchronous link commit point.
• Failure before publication leaves no requested target.
• Hidden-file cleanup failure after publication leaves the completed target and reports the established warning.
• Artifact identity and final-file digest remain separate.

Agent-aware amendment

#625 extends the lock-held detachment boundary through checkpoint association selection and trusted bundle capture. It preserves every contract above and adds exact token verification, explicit unavailable markers, declared-capability refusal, source/provider immutability evidence, portability reporting, and opaque-bundle confidentiality warnings.

This issue remains closed; #625 is the blocking amendment issue. Approved plan: b42339b3d6df869d65e4b34a8ba89f60728f8a58.