feat(Schema): preserve encodedKey across field reuse, spread, and mapFields

[patroza]

Summary

In effect v3, a struct field's encoded key rename traveled with the field. In effect-smol, renames only existed as a top-level encodeKeys mapping on the struct AST, so:

• Struct.fields.x exposed the un-renamed encoded shape
• Spreading shared field maps lost the rename
• mapFields / Class.mapFields dropped the rename
• Reusing a field across structs forced you to repeat the rename in every parent

This PR moves the rename from a struct-level concern to a field-local annotation and threads it through the type system so it survives reuse, spreading, mapFields, encodeKeys, and flip ∘ flip.

Approach

Two alternatives were considered:

1. Expose encodedFields / encodedMapFields on the struct or adding fields/mapFields to the return value of S.encodedKeys. Keeps the rename at the struct level, still does not help when a single field schema is consumed by an unrelated struct.
2. Make the rename a property of the field schema itself. A new Schema.encodedKey("foo") combinator attaches an encodedKey annotation to the field's Key annotation bag. Struct(...) discovers those annotations at construction time and folds them into an encodeKeys(...) mapping automatically. Field reuse, spread, and mapFields then "just work" because the rename rides on the field.

Option 2 won — same author ergonomics, no new struct API, and the rename is preserved through any operation that preserves the field schema.

Type-level plumbing

A new EncodedKey extends PropertyKey parameter is appended to Bottom:

export interface Bottom<
  ...,
  out EncodedOptionality extends Optionality = "required",
  out EncodedKey extends PropertyKey = never
> { readonly "~encoded.key": EncodedKey }

[changeset-bot]

🦋 Changeset detected

Latest commit: d483e23

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

This PR includes changesets to release 27 packages

Name	Type
effect	Patch
@effect/opentelemetry	Patch
@effect/platform-browser	Patch
@effect/platform-bun	Patch
@effect/platform-node-shared	Patch
@effect/platform-node	Patch
@effect/vitest	Patch
@effect/ai-anthropic	Patch
@effect/ai-openai-compat	Patch
@effect/ai-openai	Patch
@effect/ai-openrouter	Patch
@effect/atom-react	Patch
@effect/atom-solid	Patch
@effect/atom-vue	Patch
@effect/sql-clickhouse	Patch
@effect/sql-d1	Patch
@effect/sql-libsql	Patch
@effect/sql-mssql	Patch
@effect/sql-mysql2	Patch
@effect/sql-pg	Patch
@effect/sql-pglite	Patch
@effect/sql-sqlite-bun	Patch
@effect/sql-sqlite-do	Patch
@effect/sql-sqlite-node	Patch
@effect/sql-sqlite-react-native	Patch
@effect/sql-sqlite-wasm	Patch
@effect/openapi-generator	Patch

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[jdharrisnz]

Nice to see this come back. Would this work on classes too or only structs?