feat(experimental): allow null when schema is optional

[ping-maxwell]

optional already meant undefined may pass; treat null the same so callers and handlers share one nullish absence model.

[pkg-pr-new]

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commit: 6eca0b5

[greptile-apps]

Greptile Summary

This PR extends experimental optional schemas so explicit null follows the same runtime absence behavior as undefined and widens inferred outputs accordingly.

• Passes null through for optional schemas without defaults and applies defaults when present
• Widens optional output and function-schema types to include null
• Adds runtime and type-level coverage for optional null values

Confidence Score: 4/5

The PR should not merge until optional schemas with defaults expose null in their typed input contract consistently with runtime validation.

Runtime validation now deliberately accepts null and applies defaults, but InferArgs and FieldIn still reject null whenever a concrete default is declared, leaving typed callers unable to use part of the new behavior.

Files Needing Attention: packages/experimental/src/schema.ts

_{Reviews (1): Last reviewed commit: "feat(experimental): allow null when sche..." | Re-trigger Greptile}

[greptile-apps]

Defaulted inputs still reject null

When an optional schema declares a default, runtime validation accepts null and substitutes that default, but InferArgs and FieldIn still exclude null because D is concrete. Typed direct calls and object fields therefore reject inputs that the new runtime contract deliberately accepts.

Knowledge Base Used: Validation and schema contracts