fix(runner): recognise runtime errors from the exit code, not only English text

[Chemaclass]

🤔 Background

Related #998

detect_runtime_error matched English phrases — command not found and ~20 more. bash translates its diagnostics, so under any locale with the message catalogue installed none of them matched, and a genuine failure-to-run was reported as a plain assertion failure — losing the Error/Failed distinction that exists to tell those apart.

The repo runs Spanish, Brazilian and Japanese locale jobs, so this was a supported configuration, not a hypothetical.

💡 Changes

Exit codes carry the same fact without any text: the shell reserves 127 for "could not find it" and 126 for "found it, could not run it". Both are consulted only after the text scan draws a blank, so English behaviour is unchanged — including the more specific message the text produces, which is still preferred when available.

🎁 Wider than the locale case

A test that redirects the diagnostic away still exits 127. This is a real fixture in the suite:

function test_error() {
  set -e
  invalid_function_name arg1 arg2 &>/dev/null
}

Its Error message used to be empty — the text the scan needed had gone to /dev/null. It now reads command not found (exit code 127). The snapshot diff is worth reading: it replaces an empty message with the cause.

-
+command not found (exit code 127)

🔧 Two structural notes

• extract_result_counts now runs before detect_runtime_error so the exit code is available to it — safe because it's documented and verified as a pure read that commits nothing.
• The line scan moved into its own helper: it used to return from the caller on a text miss, which would have skipped the new fallback entirely. Caught because the new tests stayed red after the first implementation.

✅ Verification

4 new tests, RED first, covering: translated text + 127, translated text + 126, an ordinary failure exit code that must not classify, and English text still winning over the code.

make sa · make lint · bash build.sh bin -v → ✅ Build verified ✅ · 1717 sequential / 1676 parallel-simple-strict.