[P2-E9.10] Auto-top-up for the app-synchronizer on LocalNet

[sadiq1971]

Context. #123 step 8 asks for auto-top-up on the dedicated synchronizer to work the way it does on the global one. The fan-out is built (#40, #110) and tested in the Scala harness, with splitwell standing in for the dedicated synchronizer (SyncOperatorTrafficIntegrationTest.scala:215-232). It never runs on LocalNet:

• The LocalNet validators only set domains.global.buy-extra-traffic (app-provider/app.conf:11-14, same for app-user).
• The participants join the app-synchronizer from the console script (app-synchronizer.sc:10-11), not from domains.extra, so the app-synchronizer is not among the validator's topupTargets and the trigger never buys for it.

Deliverable.

• With -O, a LocalNet validator lists the app-synchronizer in domains.extra with a topup target. The harness does the same with a config transform (:66-89). The entry has to agree with the console script's connection, or replace it.
• LocalNetDedicatedSyncIntegrationTest checks that the validator tops up the app-synchronizer without a manual buy.

Acceptance. On LocalNet, the validator buys traffic for the app-synchronizer on its own and the operator grants it, read off the traffic state on the app-synchronizer.

Depends on. #102.

Epic: #72 · Source: #123 step 8

[sadiq1971]

LocalNet can't host this as written, so step 8 of #123 stays covered by the Scala harness.

A validator connects every domains.extra synchronizer as part of its startup (ValidatorApp.scala:222-224, SynchronizerConnector.scala:147-182). LocalNet only creates the app-synchronizer in multi-sync-startup, which waits for splice to be healthy (compose.yaml:208-216), and splice is only healthy once the app-user validator is ready (health-check.sh:7-9). Listing the app-synchronizer in that validator's domains.extra would deadlock LocalNet startup.

The harness already covers the step end to end: in SyncOperatorTrafficIntegrationTest the validator's top-up trigger buys for the registered synchronizer on its own and the operator grants it on the sequencer (:215-234), with splitwell standing in for the dedicated synchronizer. Running it on LocalNet would first need the app-synchronizer created before splice starts.

[sadiq1971]

Closing: the check this asks for already exists in the Scala integration tests, so no separate LocalNet test is needed.

SyncOperatorTrafficIntegrationTest.scala:251-271, added in canton-network/splice-multi-sync#34, with splitwell standing in for the dedicated synchronizer. After the manual and wallet buys, it resumes alice's validator top-up trigger and checks that:

• her extra-traffic limit on the dedicated sequencer rises above the manual and wallet total, so the validator bought traffic on its own and the operator granted it;
• her validator holds a ValidatorTopUpState for that synchronizer, which only the top-up fan-out creates.

It is green in the sync-operator job on the last merged PR, canton-network/splice-multi-sync#65 (run).

LocalNet stays as it is, for the startup-order reason above. Anyone deploying a validator can turn the top-up on per synchronizer with the topup block of a domains.extra entry (ValidatorAppConfig.scala:127-131), or extraDomains[].topup in the splice-validator Helm chart (validator.yaml:163-176).