fix(cdk): allow EB embedded extension write

infra/cdk/README.md

@@ -62,6 +62,13 @@ The role grants only:
   the matching version-ACL write. The grant does not cover another
   environment, another application, source bundles, object content versions,
   non-version ACL mutation, tags, or retention.
+- `s3:PutObject` on only
+  `elasticbeanstalk-us-east-1-396287094661/resources/_runtime/_embedded_extensions/shoc-backend/*`.
+  After the runtime bundle copy and version-ACL operations succeeded, attempt 8
+  of run `30448885838` showed Elastic Beanstalk materializing the application's
+  embedded-extension manifest at this application-specific prefix. CloudTrail
+  recorded the exact denied action and object ARN. The grant does not include
+  reads, deletes, ACL mutation, another application, or another bucket.
 - `s3:GetObjectAcl` on objects under the service-wide
   `arn:aws:s3:::elasticbeanstalk-*/*` namespace. AWS Support case
   `178526484500047` confirmed that `UpdateEnvironment` uses the initiating

infra/cdk/deploy-dev-stack.ts

@@ -21,6 +21,9 @@ export class DeployDevStack extends cdk.Stack {
     const runtimeVersionArn =
       `${bucketArn}/resources/environments/${ENVIRONMENT_ID}` +
       `/_runtime/_versions/${APPLICATION_NAME}/*`;
+    const embeddedExtensionArn =
+      `${bucketArn}/resources/_runtime/_embedded_extensions/` +
+      `${APPLICATION_NAME}/*`;
     const oidcProviderArn = `arn:aws:iam::${ACCOUNT_ID}:oidc-provider/token.actions.githubusercontent.com`;
 
     const deployRole = new iam.Role(this, 'GithubDeployRole', {
@@ -167,6 +170,16 @@ export class DeployDevStack extends cdk.Stack {
       }),
     );
 
+    deployRole.addToPolicy(
+      new iam.PolicyStatement({
+        effect: iam.Effect.ALLOW,
+        actions: ['s3:PutObject'],
+        // UpdateEnvironment materializes the application's embedded-extension
+        // manifest under this application-specific runtime prefix.
+        resources: [embeddedExtensionArn],
+      }),
+    );
+
     deployRole.addToPolicy(
       new iam.PolicyStatement({
         effect: iam.Effect.ALLOW,