Ambiguous type variable error during Stackage LTS migration

Goal

Upgrade a small Haskell application from GHC 9.6 to GHC 9.8, targeting a specific Stackage LTS snapshot, while avoiding downtime during the build and deployment cycle.

Constraints and Uncertainty

• Ambiguous type variable warnings may surface when the code uses custom type families or newtype wrappers not fully resolved by the snapshot.
• Reproducible builds rely on cabal v2-build --snapshot=lts-22, but the snapshot may introduce breaking changes that affect runtime behavior.
• Zero‑downtime deployment requires an atomic binary swap or a rolling restart behind a load balancer, and health checks must confirm readiness before traffic is redirected.

Questions

1. Will switching to the latest LTS snapshot automatically resolve all ambiguous type variable errors, or must custom type families be adjusted?
2. What is the safest strategy for an atomic binary replacement that guarantees no brief outage?
3. Which health‑check patterns best ensure that the new binary is fully ready before it receives live traffic?