fix: restore origin_to_use() for link spec @link directive placement

The beta1 Component->Node migration replaced
`Component { origin: schema_definition.origin_to_use(), ... }` with
`Node::new(...)`, losing the logic that chose whether the link-to-link
@link directive should go on the schema definition or an extension.

Restore the origin_to_use() call in add_to_schema so the directive gets
the correct ExtensionId, matching pre-upgrade serialization behavior.

Also remove the promote_link_spec_directive workaround that was papering
over the symptom in expand_schema.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: tninesling

apollo-federation/src/link/link_spec_definition.rs

@@ -30,6 +30,7 @@ use crate::link::spec::Version;
 use crate::link::spec_definition::SpecDefinition;
 use crate::link::spec_definition::SpecDefinitions;
 use crate::schema::FederationSchema;
+use crate::schema::SchemaElement;
 use crate::schema::position::SchemaDefinitionPosition;
 use crate::schema::type_and_directive_specification::ArgumentSpecification;
 use crate::schema::type_and_directive_specification::DirectiveArgumentSpecification;
@@ -586,10 +587,16 @@ impl LinkSpecDefinition {
             }));
         }
 
+        let directive = Node::new(Directive { name, arguments });
+        let directive = match SchemaDefinitionPosition
+            .get(schema.schema())
+            .origin_to_use()
+        {
+            Some(ext_id) => directive.with_extension_id(ext_id),
+            None => directive,
+        };
         SchemaDefinitionPosition.insert_directive_at(
-            schema,
-            Node::new(Directive { name, arguments }),
-            0, // @link to link spec should be first
+            schema, directive, 0, // @link to link spec should be first
         )?;
         Ok(())
     }

apollo-federation/src/subgraph/typestate.rs

@@ -951,12 +951,6 @@ pub(crate) fn expand_schema(schema: Schema) -> Result<FederationSchema, Federati
     trace!("new_federation_subgraph_schema: collect_links_metadata");
     schema.collect_links_metadata()?;
 
-    // The link spec's @link directive should always live on the base schema definition
-    // (not an extension) so it serializes as `schema @link(...) { ... }`. When the input
-    // only has `extend schema @link(...) @link(...)`, the parser gives every directive an
-    // ExtensionId. Promote the link-spec @link to the base definition here.
-    promote_link_spec_directive(schema.schema_mut());
-
     // Now we fill in the missing definitions
     trace!("expand_links: on_directive_definition_and_schema_parsed");
     FederationBlueprint::on_directive_definition_and_schema_parsed(&mut schema)?;
@@ -1014,27 +1008,6 @@ pub(crate) fn has_federation_spec_link(schema: &Schema) -> bool {
         .any(|d| is_fed_spec_link_directive(schema, d))
 }
 
-/// If the `@link(url: "https://specs.apollo.dev/link/...")` directive on the schema definition
-/// has an ExtensionId (because it came from `extend schema`), replace it with a copy that has
-/// no ExtensionId so it serializes on the base `schema { ... }` definition.
-fn promote_link_spec_directive(schema: &mut Schema) {
-    let link_identity_prefix = Identity::link_identity().to_string();
-    let idx = schema.schema_definition.directives.iter().position(|d| {
-        d.name == LINK_DIRECTIVE_NAME_IN_SPEC
-            && d.extension_id().is_some()
-            && d.arguments
-                .iter()
-                .find(|a| a.name == LINK_DIRECTIVE_URL_ARGUMENT_NAME.as_str())
-                .and_then(|a| a.value.as_str())
-                .is_some_and(|url| url.starts_with(&link_identity_prefix))
-    });
-    if let Some(idx) = idx {
-        let directive = &schema.schema_definition.directives[idx];
-        let promoted = directive.same_location((**directive).clone());
-        schema.schema_definition.make_mut().directives[idx] = promoted;
-    }
-}
-
 fn is_fed_spec_link_directive(schema: &Schema, directive: &Directive) -> bool {
     if directive.name != LINK_DIRECTIVE_NAME_IN_SPEC {
         return false;

apollo-federation/tests/subgraph/subgraph_validation_tests.rs

@@ -1056,11 +1056,11 @@ mod link_handling_tests {
     // There are a few whitespace differences between this and the JS version, but the more important difference is that
     // the links are added as a new extension instead of being attached to the top-level schema definition. We may need
     // to revisit that later if we're doing strict comparisons of SDLs between versions.
-    const EXPECTED_FULL_SCHEMA: &str = r#"schema @link(url: "https://specs.apollo.dev/link/v1.0") {
+    const EXPECTED_FULL_SCHEMA: &str = r#"schema {
   query: Query
 }
 
-extend schema @link(url: "https://specs.apollo.dev/federation/v2.0", import: ["@key"])
+extend schema @link(url: "https://specs.apollo.dev/link/v1.0") @link(url: "https://specs.apollo.dev/federation/v2.0", import: ["@key"])
 
 directive @link(url: String, as: String, for: link__Purpose, import: [link__Import]) repeatable on SCHEMA