fix: ensure JSON encoding uses consistent request/response format (#1158)

The JSON encoding path in handleAction was expecting a raw array for action arguments,
while the client was sending {a: [...]} format. This caused "Invalid JSON" errors when
explicitly specifying encoding: "json" in the client.

This fix ensures both JSON and CBOR encodings use the same ActionRequestSchema format
for consistency, matching the client's expected behavior.

🤖 Generated with [opencode](https://opencode.ai)

Co-authored-by: opencode <noreply@opencode.ai>

Author: julionav

packages/core/src/actor/router-endpoints.ts

@@ -430,16 +430,21 @@ export async function handleAction(
 	let actionArgs: unknown[];
 	if (encoding === "json") {
 		try {
-			actionArgs = await c.req.json();
+			const body = await c.req.json();
+
+			// Validate using the action schema
+			const result = protoHttpAction.ActionRequestSchema.safeParse(body);
+			if (!result.success) {
+				throw new errors.InvalidActionRequest("Invalid action request format");
+			}
+
+			actionArgs = result.data.a;
 		} catch (err) {
+			if (err instanceof errors.InvalidActionRequest) {
+				throw err;
+			}
 			throw new errors.InvalidActionRequest("Invalid JSON");
 		}
-
-		if (!Array.isArray(actionArgs)) {
-			throw new errors.InvalidActionRequest(
-				"Action arguments must be an array",
-			);
-		}
 	} else if (encoding === "cbor") {
 		try {
 			const value = await c.req.arrayBuffer();
@@ -496,7 +501,10 @@ export async function handleAction(
 
 	// Encode the response
 	if (encoding === "json") {
-		return c.json(output as Record<string, unknown>);
+		const responseData = {
+			o: output, // Use the format expected by ResponseOkSchema
+		};
+		return c.json(responseData);
 	} else if (encoding === "cbor") {
 		// Use serialize from serde.ts instead of custom encoder
 		const responseData = {