skip conditional selection separation when extractAllFieldsToTypesCompact is enabled

[ikusakov2]

Overview

When extractAllFieldsToTypesCompact is enabled, conditional fragment
spreads (@skip/@include) and conditional inline fragments should NOT
be separated into selectionNodesByTypeNameConditional. They should be
merged into the base selectionNodesByTypeName like regular (unconditional)
selections.

Problem

The extractAllFieldsToTypesCompact option is designed to produce
apollo-tooling-compatible type output, where all fields from an operation
(including those from conditional fragments) appear in a single flat type.
Apollo-tooling never differentiated conditional fields as optional.

However, commit introducing conditional selection separation (which makes
conditional fragment fields optional via intersection types) is incompatible
with extractAllFieldsToTypesCompact because:

1. Processing conditional selections separately causes the same type name
   to be generated multiple times (once from the base selection, once from
   each conditional fragment), resulting in duplicate export type
   declarations — a syntax error.

2. Conditional fragment fields from nested fragment spreads don't propagate
   transitively, causing missing fields in generated types.

3. The _seenFieldNames deduplication in buildParentFieldName prevents
   naming conflicts but not duplicate type declarations.

Fix

When extractAllFieldsToTypesCompact is enabled, skip the conditional
check in flattenSelectionSet and treat all selections uniformly. This
restores the alpha-version behavior where conditional and unconditional
selections were processed together, producing a single merged type with
all fields.

This is semantically correct for extractAllFieldsToTypesCompact because:

• The option targets apollo-tooling compatibility
• Apollo-tooling never made conditional fields optional
• Users of this option expect flat types matching the GraphQL response shape

[changeset-bot]

🦋 Changeset detected

Latest commit: 2d47844

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@graphql-codegen/visitor-plugin-common	Patch

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