[v3] Runtime calls fail with 422 / “Unable to parse request body as JSON”

[FoxEdit]

Description

Hello
After upgrading the frontend runtime package from @wailsio/runtime@3.0.0-alpha.76 to 3.0.0-alpha.77, all runtime/binding calls fail at runtime. Downgrading back to alpha.76 fixes the issue immediately without any code changes.

To Reproduce

Install latest wails v3 (current latest resolves to v3.0.0-alpha.46)
go install github.com/wailsapp/wails/v3/cmd/wails3@latest

Install runtime package alpha.77 in the frontend:
npm i @wailsio/runtime

Call any bound method

Expected behaviour

Runtime calls should succeed

Actual behavior:

Browser console:
Failed to load resource: the server responded with a status of 422 (Unprocessable Entity)
useFolderStore.tsx:77 Error: Invalid runtime call: Unable to parse request body as JSON: unexpected end of JSON input at runtimeCallWithID (runtime.js:55:15)

Wails log:
Dec 14 17:57:02.479 INF handleWebViewRequest: Processing request url="http://wails.localhost:9245/wails/runtime?object=0&method=0&args=%7B%22call-id%22%3A%22CJjVLVqelkCkQWyNvON7_%22%2C%22methodID%22%3A712950749%2C%22args%22%3A%5B%22%22%5D%7D"
Dec 14 17:57:02.479 ERR Invalid runtime call: Unable to parse request body as JSON: unexpected end of JSON input

Screenshots

No response

Attempted Fixes

Downgrading back to alpha.76

System Details

Wails (v3.0.0-alpha.46)  Wails Doctor 

# System 

┌──────────────────────────────────────────────────────────────────────────────┐
| Name              | Windows 10 Pro                                           |
| Version           | 2009 (Build: 22631)                                      |
| ID                | 23H2                                                     |
| Branding          | Windows 11 Pro                                           |
| Platform          | windows                                                  |
| Architecture      | amd64                                                    |
| Go WebView2Loader | true                                                     |
| WebView2 Version  | 143.0.3650.80                                            |
| CPU               | Intel(R) Core(TM) i7-7700K CPU @ 4.20GHz                 |
| GPU 1             | NVIDIA GeForce GTX 1080 (NVIDIA) - Driver: 32.0.15.7270  |
| Memory            | 16GB                                                     |
└──────────────────────────────────────────────────────────────────────────────┘

# Build Environment 

┌────────────────────────────────┐
| Wails CLI    | v3.0.0-alpha.46 |
| Go Version   | go1.24.1        |
| -buildmode   | exe             |
| -compiler    | gc              |
| CGO_CFLAGS   |                 |
| CGO_CPPFLAGS |                 |
| CGO_CXXFLAGS |                 |
| CGO_ENABLED  | 1               |
| CGO_LDFLAGS  |                 |
| GOAMD64      | v1              |
| GOARCH       | amd64           |
| GOOS         | windows         |
└────────────────────────────────┘

# Dependencies 

┌────────────────────────────────────────────────────────────────────────────────┐
| MakeAppx.exe (Windows SDK) | Not Installed                                     |
| MSIX Packaging Tool        | Not Installed                                     |
| SignTool.exe (Windows SDK) | Not Installed                                     |
| npm                        | 10.9.2                                            |
| NSIS                       | Not Installed                                     |
| docker                     | *Not installed (optional - for cross-compilation) |
|                                                                                |
└─────────────────────────── * - Optional Dependency ────────────────────────────┘

# Checking for issues 

 SUCCESS  No issues found

# Diagnosis 

 SUCCESS  Your system is ready for Wails development!

Need documentation? Run: wails3 docs
 ♥   If Wails is useful to you or your company, please consider sponsoring the project: wails3 sponsor

Additional context

No response