fix(OmegaForm): deep-fill defaults for nullable nested structs

[MakhBeth]

Problem

A S.NullOr(S.Struct(...)) field has no slot in the form value until a child is filled. Once it materialises (the user fills one child), its untouched nullable siblings are still undefined — which strict S.NullOr(...) children reject with a spurious "field must not be empty" error, blocking submission.

Fix

New fillNestedDefaults (AST walk) backfills the untouched children of a materialised nullable struct with their schema default (or null). Applied in three places:

• validation and decoding — via normalizeFormValue, so submit/validate see the normalized value;
• live form state — normalizeNullableStructs() is called from OmegaInternalInput.handleChange (the only point a struct can materialise), so values stays consistent. No perpetual watch.

The always-present root struct is left untouched; only children reached through a nullable union are filled. Discriminated unions are matched by _tag; ambiguous unions are left alone.

Tests

• Defaults.values.test.ts — unit tests for fillNestedDefaults (materialised struct, tagged-union safety, array elements, reference-preservation).
• NullableNestedStructValidation.test.ts — regression repro: submits when only one child of a nullable struct is filled; keeps an untouched struct as null.

[pkg-pr-new]

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@effect-app/cli

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effect-app

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@effect-app/eslint-codegen-model

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@effect-app/eslint-shared-config

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@effect-app/infra

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@effect-app/vue

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@effect-app/vue-components

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commit: 59ff901

[Copilot]

Pull request overview

This PR fixes OmegaForm submission/validation failures caused by S.NullOr(S.Struct(...)) fields “materializing” mid-edit (after one child is filled) while their untouched nullable siblings remain undefined and fail strict S.NullOr(...) decoding/validation.

Changes:

• Add fillNestedDefaults (AST walk) to backfill missing nullable children (to schema defaults or null) only for structs reached through nullable unions.
• Normalize values before validation and decoding, and keep live form state consistent by invoking normalization after field changes.
• Add regression/unit tests plus a Storybook story and a changeset.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/vue-components/stories/OmegaForm/NullableNestedStruct.vue	New story demonstrating nullable nested-struct materialization behavior.
packages/vue-components/stories/OmegaForm.stories.ts	Registers the new NullableNestedStruct story.
packages/vue-components/src/components/OmegaForm/useOmegaForm.ts	Normalizes values for schema validation/decoding; adds live-state normalization hook on the form instance.
packages/vue-components/src/components/OmegaForm/types.ts	Exposes normalizeNullableStructs() on the OmegaForm API type.
packages/vue-components/src/components/OmegaForm/OmegaInternalInput.vue	Calls form.normalizeNullableStructs() after field changes to keep values consistent.
packages/vue-components/src/components/OmegaForm/meta/defaults.ts	Implements fillNestedDefaults AST-based backfilling for materialized nullable structs (reference-preserving).
packages/vue-components/tests/OmegaForm/NullableNestedStructValidation.test.ts	Regression test proving submission succeeds with only one nullable child filled; untouched struct remains null.
packages/vue-components/tests/OmegaForm/Defaults.values.test.ts	Unit tests for fillNestedDefaults behavior (tagged unions, arrays, reference preservation).
.changeset/omega-nullable-nested-struct.md	Patch changeset entry for @effect-app/vue-components.

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