refactor: dedupe runtime error formatting

src/plugin-sdk/run-command.ts

@@ -1,3 +1,4 @@
+import { formatErrorMessage } from "../infra/errors.js";
 import { runCommandWithTimeout } from "../process/exec.js";
 
 export type PluginCommandRunResult = {
@@ -40,7 +41,7 @@ export async function runPluginCommandWithTimeout(
     return {
       code: 1,
       stdout: "",
-      stderr: error instanceof Error ? error.message : String(error),
+      stderr: formatErrorMessage(error),
     };
   }
 }

src/plugin-sdk/webhook-request-guards.ts

@@ -1,4 +1,5 @@
 import type { IncomingMessage, ServerResponse } from "node:http";
+import { formatErrorMessage } from "../infra/errors.js";
 import {
   installRequestBodyLimitGuard,
   isRequestBodyLimitError,
@@ -268,8 +269,7 @@ export async function readWebhookBodyOrReject(params: {
     return respondWebhookBodyReadError({
       res: params.res,
       code: "INVALID_BODY",
-      invalidMessage:
-        params.invalidBodyMessage ?? (error instanceof Error ? error.message : String(error)),
+      invalidMessage: params.invalidBodyMessage ?? formatErrorMessage(error),
     });
   }
 }