feat(ack): support Draft 2020-12 runtime import and export

docs/api-reference/index.mdx

@@ -36,10 +36,9 @@ Entry point for creating schemas. See [Schema Types](../core-concepts/schemas.md
 - `Ack.any()`: Creates an `AnySchema` that accepts any non-null JSON-safe
   value. Chain `.nullable()` to allow `null`.
 - `Ack.fromJsonSchema(Object document, {Uri? baseUri, Map<Uri, Object>
-  documents = const {}})`: Strictly imports a decoded draft 2020-12
-  JSON Schema. Referenced documents must be supplied explicitly; Ack never
-  fetches files or URLs. The supported `date-time` format is asserted; see
-  [format import](../guides/json-schema-integration.mdx#importing-format).
+  documents = const {}, bool assertFormats = false})`: Imports a decoded draft 2020-12 JSON
+  Schema. Referenced documents must be supplied explicitly; Ack never fetches
+  files or URLs. Formats are annotations unless assertions are enabled.
 - `Ack.map(AckSchema valueSchema)`: Creates a `MapSchema` for a JSON object
   with arbitrary string keys whose values all match `valueSchema`. Use
   `Ack.map(Ack.any().nullable())` for a `JsonMap`.
@@ -121,10 +120,16 @@ For non-`num` boundary types (e.g. numeric strings), use
 
 ### Utility Methods
 
-- `Map<String, Object?> toJsonSchema()`: Returns a Draft-7 JSON Schema map via
-  the canonical `AckSchemaModel` boundary.
+- `Map<String, Object?> toJsonSchema()`: Returns a JSON Schema representation
+  via the canonical `AckSchemaModel` boundary, preserving imported Draft 2020-12
+  resources by default and emitting Draft-7 for native schemas.
+- `Map<String, Object?> toJsonSchemaDraft7()`: Exports imported schemas using
+  the legacy Draft-7 `definitions` / `$ref` lowering when possible.
 - `AckSchemaModel toSchemaModel()`: Returns the canonical, target-independent
-  boundary model for schema adapters, including export warnings.
+  boundary model for schema adapters, preserving imported Draft 2020-12
+  resources by default.
+- `AckSchemaModel toSchemaModelDraft7()`: Returns the matching model for the
+  legacy Draft-7 lowering.
 - `Map<String, Object?> toMap()`: Serializes the schema for debugging.
 
 See also [Schema Types](../core-concepts/schemas.mdx) for detailed usage examples.
@@ -499,7 +504,7 @@ Canonical export model for Ack schemas.
 
 - Created by `schema.toSchemaModel()`.
 - Represents the boundary/export shape, JSON-compatible defaults, discriminator metadata, target-independent constraints, and export warnings.
-- `schema.toSchemaModel().toJsonSchema()` returns the same Draft-7 map as `schema.toJsonSchema()`.
+- `schema.toSchemaModel().toJsonSchema()` returns the same JSON Schema map as `schema.toJsonSchema()`. Use `toSchemaModelDraft7()` for legacy Draft-7 lowering of imported schemas.
 - Adapters that need a JSON map should call `schema.toJsonSchema()`; adapters for non-JSON targets should convert from `AckSchemaModel` rather than traversing `AckSchema` subclasses directly.
 
 ### `AnySchema`

packages/ack/CHANGELOG.md

@@ -2,6 +2,14 @@
 
 ### Added
 
+* `Ack.fromJsonSchema()` now validates and round-trips the complete required
+  Draft 2020-12 test suite, including dynamic references, unevaluated keywords,
+  and offline standard meta-schemas. `assertFormats: true` enables optional
+  format assertions.
+* `toJsonSchema()` and `toSchemaModel()` now preserve imported Draft 2020-12
+  resources by default. `toJsonSchemaDraft7()` and `toSchemaModelDraft7()`
+  retain the legacy 1.x Draft-7 lowering for imported schemas when compatible;
+  imports that require 2020-12-only semantics reject Draft-7 lowering explicitly.
 * `Ack.fromJsonSchema()` now supports `multipleOf` for `number` and `integer`
   schemas. Non-positive or non-numeric `multipleOf` values fail import with an
   `invalid_schema` diagnostic.

packages/ack/lib/src/ack.dart

@@ -11,16 +11,20 @@ final class Ack {
   ///
   /// [document] must be a map or boolean, not a JSON string. Referenced
   /// [documents] are supplied by retrieval URI; no files or URLs are fetched.
-  /// The supported `date-time` format is asserted. Other formats remain
-  /// unsupported. Unsupported semantics throw [JsonSchemaImportException].
+  /// [assertFormats] opts into format assertions under the standard dialect;
+  /// a supplied dialect requiring the format-assertion vocabulary also enables
+  /// them. Unknown asserted formats are rejected when compiling.
+  /// Unsupported semantics throw [JsonSchemaImportException].
   static AckSchema<Object, Object> fromJsonSchema(
     Object document, {
     Uri? baseUri,
     Map<Uri, Object> documents = const {},
+    bool assertFormats = false,
   }) => ImportedJsonSchema.fromDocument(
     document,
     baseUri: baseUri,
     documents: documents,
+    assertFormats: assertFormats,
   );
 
   /// Creates a string schema. Boundary and runtime are both `String`.