fix: Update nonce schema with IPLD bytes (#593)

# Description

This PR makes the following changes:

- [x] Update the nonce schema one of IPLD bytes or empty string
- [x] Add workflow validation test that uses a nonce

The schema will be updated by the schemas action, but as a preview it
looks like this:

```json
"nnc": {
  "description": "A 12-byte or 16-byte nonce encoded as IPLD bytes. Use empty string for no nonce.",
  "oneOf": [
    {
      "$ref": "#/definitions/ipld_bytes"
    },
    {
      "type": "string",
      "const": ""
    }
  ]
},
```
```json
"ipld_bytes": {
  "title": "IPLD bytes",
  "description": "Base64 encoded binary",
  "type": "object",
  "properties": {
    "/": {
      "type": "object",
      "properties": {
        "bytes": {
          "type": "string"
        }
      }
    }
  }
},
```

## Type of change

- [x] Bug fix (non-breaking change that fixes an issue)
- [ ] This change requires a documentation update (schemas will be
updated by the action)

## Test plan (required)

A new `validate_and_parse_workflow_with_nonce` has been added that
validates a workflow with a task that uses a nonce.

homestar-invocation/src/task/instruction/nonce.rs

@@ -2,7 +2,7 @@
 //!
 //! [Instruction]: super::Instruction
 
-use crate::{Error, Unit};
+use crate::{ipld::schema, Error, Unit};
 use const_format::formatcp;
 use enum_as_inner::EnumAsInner;
 use generic_array::{
@@ -16,6 +16,7 @@ use schemars::{
     JsonSchema,
 };
 use serde::{Deserialize, Serialize};
+use serde_json::json;
 use std::{borrow::Cow, fmt, module_path};
 use uuid::Uuid;
 
@@ -103,17 +104,29 @@ impl JsonSchema for Nonce {
         Cow::Borrowed(formatcp!("{}::Nonce", module_path!()))
     }
 
-    fn json_schema(_gen: &mut SchemaGenerator) -> Schema {
-        let schema = SchemaObject {
-            instance_type: Some(SingleOrVec::Single(InstanceType::String.into())),
+    fn json_schema(gen: &mut SchemaGenerator) -> Schema {
+        let mut schema = SchemaObject {
+            instance_type: None,
             metadata: Some(Box::new(Metadata {
                 description: Some(
-                    "A 12-byte or 16-byte nonce. Use empty string for no nonce.".to_string(),
+                    "A 12-byte or 16-byte nonce encoded as IPLD bytes. Use empty string for no nonce.".to_string(),
                 ),
                 ..Default::default()
             })),
             ..Default::default()
         };
+
+        let empty_string = SchemaObject {
+            instance_type: Some(SingleOrVec::Single(InstanceType::String.into())),
+            const_value: Some(json!("")),
+            ..Default::default()
+        };
+
+        schema.subschemas().one_of = Some(vec![
+            gen.subschema_for::<schema::IpldBytesStub>(),
+            Schema::Object(empty_string),
+        ]);
+
         schema.into()
     }
 }

homestar-runtime/src/runner/file.rs

@@ -116,4 +116,26 @@ mod test {
             workflow_file.validate_and_parse().await.unwrap();
         assert_eq!(workflow, newly_validated_workflow);
     }
+
+    #[tokio::test]
+    async fn validate_and_parse_workflow_with_nonce() {
+        let path = PathBuf::from("./fixtures/test_nonce.json");
+        let config = Resources::default();
+        let (instruction, _) = test_utils::wasm_instruction_with_nonce::<Arg>();
+
+        let task = Task::new(
+            RunInstruction::Expanded(instruction.clone()),
+            config.clone().into(),
+            UcanPrf::default(),
+        );
+
+        let workflow = Workflow::new(vec![task]);
+
+        workflow.to_file(path.display().to_string()).unwrap();
+        let workflow_file = ReadWorkflow { file: path.clone() };
+
+        let (validated_workflow, _settings) = workflow_file.validate_and_parse().await.unwrap();
+
+        assert_eq!(workflow, validated_workflow);
+    }
 }