refactor(k8s): consolidate the 4 actions#341 throw sites via formatError()

actions#341 (merged 2026-06-03) replaced `JSON.stringify(error)` with
`error instanceof Error ? error.message : String(error)` at four throw
sites in k8s/index.ts. Now that `formatError()` ships in k8s/utils.ts
(introduced in the same PR as this commit), use it instead — a strict
superset that additionally:

  - extracts `response.body.message` (and `reason`) from
    @kubernetes/client-node API errors at `waitForPodPhases` and
    `waitForJobToComplete`, which currently surface a generic
    "HTTP request failed" instead of the actual K8s server message;
  - never throws on circular references (the original actions#329 bug).

Also drops the `.stack ?? .message` branch in formatError() and returns
just `.message` for Error instances. This keeps the format predictable
(no stack trace dumped into user-visible CI errors) and lets actions#341's
`error-serialization-test.ts` continue to pass unchanged.

Author: remidebette

packages/k8s/src/k8s/index.ts

@@ -14,6 +14,7 @@ import {
 } from '../hooks/constants'
 import {
   PodPhase,
+  formatError,
   mergePodSpecWithOptions,
   mergeObjectMeta,
   fixArgs,
@@ -517,7 +518,7 @@ export async function execCpToPod(
       attempt++
       if (attempt >= 30) {
         throw new Error(
-          `cpToPod failed after ${attempt} attempts: ${error instanceof Error ? error.message : String(error)}`
+          `cpToPod failed after ${attempt} attempts: ${formatError(error)}`
         )
       }
       await sleep(1000)
@@ -614,7 +615,7 @@ export async function execCpFromPod(
       attempt++
       if (attempt >= 30) {
         throw new Error(
-          `execCpFromPod failed after ${attempt} attempts: ${error instanceof Error ? error.message : String(error)}`
+          `execCpFromPod failed after ${attempt} attempts: ${formatError(error)}`
         )
       }
       await sleep(1000)
@@ -661,7 +662,7 @@ export async function waitForJobToComplete(jobName: string): Promise<void> {
         return
       }
     } catch (error) {
-      throw new Error(`job ${jobName} has failed: ${error instanceof Error ? error.message : String(error)}`)
+      throw new Error(`job ${jobName} has failed: ${formatError(error)}`)
     }
     await backOffManager.backOff()
   }
@@ -784,7 +785,7 @@ export async function waitForPodPhases(
     }
   } catch (error) {
     throw new Error(
-      `Pod ${podName} is unhealthy with phase status ${phase}: ${error instanceof Error ? error.message : String(error)}`
+      `Pod ${podName} is unhealthy with phase status ${phase}: ${formatError(error)}`
     )
   }
 }

packages/k8s/src/k8s/utils.ts

@@ -331,7 +331,7 @@ export function formatError(err: unknown): string {
   }
 
   if (err instanceof Error) {
-    return err.stack ?? err.message
+    return err.message
   }
 
   // Primitives serialise more readably via String() than JSON.stringify