Changelog - 2026-10-11

Error messages fill their placeholders

Enhancement Behavior Change

In one line. The response message of an intentional error is ready to show.

throw getError({
  message: { text: 'Only %{available} left of %{variantId}.', code: 'stock.unavailable' },
  messageArgs: { available: 2, variantId: 'V1' },
  statusCode: 409,
});

{
  "message": "Only 2 left of V1.",
  "normalized": {
    "text": "Only %{available} left of %{variantId}.",
    "code": "stock.unavailable",
    "args": { "available": 2, "variantId": "V1" }
  }
}

Before, message was the raw template. A client that fell back to message for a code it could not translate showed %{available} to the user.

What changed

• message is filled. The error middleware replaces each %{key} with String(args[key]) from normalized.args.
• normalized.text keeps the template. A client that translates code + args works unchanged. A transform still changes only normalized.text.
• Error.message and the log keep the template. An arg value stays in the args map, where the log redacts secret-shaped keys.
• A missing arg stays as written. Outside production, the middleware logs one warning that names the code and the missing keys. Production stays silent.
• Only an intentional error is filled. A validation, database or unexpected error writes its own text, and that text passes through unchanged.

A route error inside a Worker host goes through the same middleware, so it answers the same body.

Who is affected

• A client that shows message. It now shows readable text. No change needed.
• A client or test that compares message with the catalog template. Compare normalized.text instead, or expect the filled text.

Details

The fill runs in the response only. Filling Error.message too would print each value inline in the log line, outside the redacted args map.

Files: packages/kernel/src/base/middlewares/app-error/app-error.middleware.ts, packages/inversion/src/modules/error/message-template.ts

See Read the error response shape for the full response.