[P2-E9.8] User story: synchronizer upgrades (LSU) #125

A dedicated synchronizer takes a Splice release that needs an LSU, without breaking participants that are also on the gsync.

Prerequisite: a registered, initialized dedicated synchronizer (#122), and a release with protocol changes.

Tick a box once we have walked that step end to end. The refs are the issues that build it.

• Operator reads in the release notes that the new release needs an LSU. [P2-E8.4] Operator-driven LSU for the dedicated synchronizer #36
• Operator starts the LSU from the sync-operator app, giving a freeze time and an upgrade time.
• The app coordinates the LSU on its own, the way the SV app does for the gsync.
• Participants on both synchronizers keep working either way round, upgraded together or not, as long as they stay within one protocol version.

Step 3 is built under #36 (canton-network/splice-multi-sync#58).

Acceptance. An LSU driven from the sync-operator app completes on the two-sync LocalNet, and a dual-homed participant transacts on both synchronizers before, between and after the two upgrades, in both orders. Balances and MemberTraffic survive, migration id pinned at 0 throughout. #83, #115

Depends on. #36, #113, #102.

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Epic: #72 · Source: Appendix C story 6, 2026-08 Extension Traffic Manager Technical Design.md