Deferred: Connected System full sync preview surface

[JayVDZ]

Summary

Deferred by decision (25 Aug 2026): the administrator-facing surface for previewing a full synchronisation of a whole Connected System is a nice-to-have and does not ship with the per-object Sync Preview surface (#1519). This issue is the durable record so the capability is not lost.

What already exists

The engine method is built and tested: JimApplication.SyncPreview.PreviewFullSyncAsync(connectedSystemId, FullSyncPreviewOptions?) walks the population under the zero-side-effect backstops, returning FullSyncPreviewResult (whole-population counts, bounded per-category sample trees, explicit work budget with truncation flagged). No portal, REST or PowerShell caller exists, deliberately.

When picked up

• Dispatch and retention follow Configuration change preview (impact analysis): unified framework and coverage map #827's model (estimate vs threshold, JIM.Worker task attached to an Activity, results persisted as rows on the preview Activity under RPEI retention); the analysis is on Sync Preview: complete the destructive cascade and ship the per-object administrator surface (portal, REST, PowerShell) #1519's history.
• Verify PreviewFullSyncAsync constant factors at Scale template (100K+) on a 20 GB+ host #1520 (Scale template constant-factor verification) must be run before this ships; its figures set the budget and threshold defaults.
• Surface parity applies: portal, REST and PowerShell together.