chore(bash): record background failure-status debt

A background spawn failure currently resembles a signal-less kill, while a sandbox-runner failure resembles a completed wrapper exit. The generic task adapter cannot mark both as failed without a distinct infrastructure-failure fact on BashProcess. Mapping the existing states differently would also risk treating ordinary nonzero command exits as infrastructure failures.

Keep the current truthful model-visible diagnostics and record a scoped TODO at processOutcome. The eventual fix must widen the BashProcess seam first, then map spawn and runner failures to TaskOutcome failed while preserving completed for real command exits.

packages/bash/tool-bash/src/index.ts

@@ -221,6 +221,11 @@ export function renderProcessRead(
  * @returns the outcome for the `ctx.tasks` registration.
  */
 export function processOutcome(proc: BashProcess): { status: 'completed' | 'killed'; detail: string } {
+  // TODO(background-infrastructure-outcome): widen BashProcess with an explicit
+  // infrastructure-failure outcome, then map spawn failures and
+  // sandbox.runnerFailed to task `failed`. The current seam aliases a spawn
+  // failure with a signal-less kill and a runner failure with an ordinary
+  // wrapper exit; real nonzero command exits must remain `completed`.
   if (proc.status === 'killed') {
     return { status: 'killed', detail: proc.signal !== null ? `signal: ${proc.signal}` : 'killed before exit' }
   }