Fallback to available shell when run_terminal_command shell is missing

[siewcapital]

Summary

• make the terminal tool choose the first available Unix shell from SHELL, /bin/bash, /bin/sh, and /bin/ash
• avoid hard-failing when SHELL points to a missing path or /bin/bash is not installed
• add a regression test that verifies command execution still succeeds when SHELL is invalid

Why

In remote/devcontainer setups, some environments do not expose the expected shell path. Falling back to an available shell prevents spawn ... ENOENT failures and keeps terminal tooling usable.

Closes #11129

---

Summary by cubic

Gracefully fall back to an available Unix shell in runTerminalCommand when SHELL is invalid or /bin/bash is missing, preventing spawn ENOENT errors in remote/devcontainer environments. Fixes #11129.

• Bug Fixes
  • Select the first available shell from $SHELL, /bin/bash, /bin/sh, or /bin/ash (non-absolute shells are resolved via PATH).
  • Added a regression test for invalid SHELL and ensured tests restore SHELL cleanly when it was unset.

^{Written for commit 63cef14. Summary will update on new commits.}

[github-actions]

Thank you for your submission, we really appreciate it. Like many open-source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution. You can sign the CLA by just posting a Pull Request Comment same as the below format.

---

I have read the CLA Document and I hereby sign the CLA

---

_{You can retrigger this bot by commenting recheck in this Pull Request. Posted by the CLA Assistant Lite bot.}

[cubic-dev-ai]

1 issue found across 2 files

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="core/tools/implementations/runTerminalCommand.vitest.ts">

<violation number="1" location="core/tools/implementations/runTerminalCommand.vitest.ts:162">
P1: Environment variable cleanup may leak SHELL state - assigning undefined to process.env creates string 'undefined'</violation>
</file>

_{Reply with feedback, questions, or to request a fix. Tag @cubic-dev-ai to re-run a review.}