[2520] Prove expiry transition state is scoped

[Chris0Jeky]

Summary

• add a service-level regression for archived-board skip transition state
• prove one service instance logs the repeated count once then emits the debug continuation
• prove a fresh service instance starts its own informational transition

Proof

• focused detector passes 1/1 after compile
• controlled static-field mutation made the focused detector fail (1 info instead of 2), then production code was restored byte-for-byte
• AutomationProposalServiceTests: 152 passed
• dotnet test -c Release -m:1 on the focused class
• git diff --check

The production service is unchanged; this is a test-only proof slice.

Refs #2520

No issue close or merge requested; this PR is intentionally left open for review.

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