fix(cli): propagate cancellation into shell command injections - #29459

Summary

!{...} shell injections inside custom commands were executed with a brand-new AbortController().signal, so nothing could ever abort them: the caller's cancellation never reached the subprocess, and no injection had a budget of its own. A custom command containing a hung command (for example !{sleep 600}) therefore blocked the whole prompt pipeline with no way out — even though ShellProcessor already handles aborted results and appends [Shell command '…' aborted], which is what a cancelled command was always meant to produce.

Details

Each injection now runs under the caller's signal combined with a per-command ceiling (AbortSignal.any([timeout, caller]), the pattern already used elsewhere in this repo, e.g. gitUtils.ts):

export const SHELL_INJECTION_TIMEOUT_MS = 60_000;

function getCommandAbortSignal(caller?: AbortSignal): AbortSignal {
  const timeoutSignal = AbortSignal.timeout(SHELL_INJECTION_TIMEOUT_MS);
  return caller ? AbortSignal.any([timeoutSignal, caller]) : timeoutSignal;
}

The caller's signal is threaded through a new optional CommandContext.signal, wired from the non-interactive abort controller in nonInteractiveCliCommands.ts. IPromptProcessor.process is unchanged, so there is no cross-package interface change.

Two deliberate choices worth your review: the 60_000 ceiling matches the existing COMMAND_TIMEOUT_MS used by core's auth value resolver, and a pipeline with no per-command budget is precisely what made the hang unrecoverable — but it is a new bound on injections, so say the word if you would rather keep this PR to signal propagation only, or make the ceiling configurable. The interactive path has no signal to hand yet, so there the ceiling is the only escape; wiring the interactive abort signal through to CommandContext is a natural follow-up and is left out here to keep the change small.

Related Issues

Fixes #29314

How to Validate

Red before the source change (only the new tests added):

npx vitest run src/services/prompt-processors/shellProcessor.test.ts   # 2 failed | 35 passed
  should forward the caller signal to shell execution
    → expected false to be true            # the signal passed to execute never aborts
  should abort a hung command once the injection timeout elapses
    → expected "timeout" to be called with arguments: [ Any<Number> ]
      Number of calls: 0                    # no timeout signal existed at all

Green after:

npx tsc --noEmit                                  # clean (packages/cli)
npx eslint <the four changed files>               # clean
npx vitest run src/services/prompt-processors/shellProcessor.test.ts   # 37 passed

Regression surfaces: src/ui/hooks/slashCommandProcessor.test.tsx, src/nonInteractiveCli.test.ts, src/ui/commands, src/services → 690 passed; src/services/FileCommandLoader.test.ts + src/services/prompt-processors → 118 passed. Manual: a custom command containing !{sleep 600} no longer holds the prompt pipeline open — cancelling (headless) or exceeding the ceiling terminates the command and processing continues with the aborted marker.

Pre-Merge Checklist

• Updated relevant documentation and README (if needed) — not needed, no user-facing docs for this path
• Added/updated tests (if needed)
• Noted breaking changes (if any) — none; injections are now bounded at 60s, see Details
• Validated on required platforms/methods:
  • MacOS
    • npm run
    • npx
    • Docker
    • Podman
    • Seatbelt
  • Windows
    • npm run
    • npx
    • Docker
  • Linux
    • npm run
    • npx
    • Docker

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