Helm upgrade with --reuse-values ignores updated chart defaults

During a Helm upgrade, the --reuse-values flag causes Helm to retain the previously released values and apply only the new --set or -f overrides. The chart's values.yaml is not re-evaluated unless explicitly included again. This behavior is documented but creates a practical gap when a chart maintainer changes default values between versions.

If a chart updates a default (for example, changing a resource limit or enabling a new feature flag), an upgrade with --reuse-values silently preserves the old default. The operator must know which defaults changed and manually re-apply them, or omit --reuse-values and re-specify every prior override. Neither approach is clearly guided by the tooling.

What is the recommended pattern for adopting new chart defaults while preserving intentional overrides? Does Helm provide a mechanism to diff the previous computed values against the new chart defaults before upgrading? How can an automation pipeline detect when a chart's defaults have drifted from the released values?