fix(experimental): widen var-bound inputs from parent scope and customize

[ping-maxwell]

Used endpoints defined against a base var should pick up later parent-mounted v.extend and customize shadows at both the type and validation layers.

[pkg-pr-new]

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npm i https://pkg.pr.new/better-call@203

commit: b61661b

[greptile-apps]

Greptile Summary

The PR widens var-bound endpoint inputs using extensions and customized same-name vars inherited from parent builders.

• Adds full-chain type rewriting for functions exposed through nested builders.
• Treats mounted customized vars as runtime input extensions.
• Adds type and runtime tests for additive customized fields and parent-mounted extensions.

Confidence Score: 4/5

The PR should not merge until replacement customizations preserve shadow precedence instead of producing impossible input types and order-dependent runtime values.

Same-name customized schemas are intersected with their base declarations and both are applied at runtime, which breaks the existing replace customization path whenever fields are removed or changed.

Files Needing Attention: packages/experimental/src/module.ts, packages/experimental/src/fn.ts

_{Reviews (1): Last reviewed commit: "fix(experimental): widen var-bound input..." | Re-trigger Greptile}

[greptile-apps]

Replacement shadows become intersections

When a mounted var and its same-name customized re-export use replace to remove a field or change its type, VarArgsInScope and VarValuesInScope intersect both declarations instead of applying shadow precedence. For example, replacing { id: string } with { id: number } produces { id: never } at the call site and in c.input, while runtime applies both schemas in module order, rejecting valid customized calls or producing values that disagree with the declared type.