Retrofit of #99 for a chart that already carries a values.schema.json,
plus the schema type change that goes with it.
An override written without children is YAML null. Where the chart
defines a default, Helm's coalescing deletes the default before schema
validation runs, so the schema never sees the null and cannot reject it:
the container rendered "securityContext: null" - unhardened, healthy,
silent. Where the chart defines no default (resources.limits), the null
survives into validation and a strict "object" type aborted the render.
The defaultedDict helper from #96 handles the first case; widening the
types of exactly these blocks to ["object", "null"] handles the second.
All other keys stay strict, additionalProperties: false is untouched.
The probes address the container port by name, so a rebuilt default probe
needs no further context.
Rendering with normal values is byte-identical to 5.0.0.
additionalProperties: false on every chart-owned object level, so a key
the chart does not read is rejected at render time instead of being
silently ignored. Objects passed verbatim into the pod spec (probes,
securityContext, global) stay open - Kubernetes owns their schema there.
Major bump: a schema can break existing deployments that carry dead keys.
Refs #68
jklein