fix(tests): force the non-TTY condition instead of inheriting it

[MCamner]

Symptom

mqlaunch → SELF-CHECK stops here:

SMOKE: gitmerge-safe safety contract
...
[9/10] non-interactive execution is refused

Smoke checks failed.

Step 10 never prints. Run from a pipe or CI the same suite passes.

Cause

The gate in gitmerge-safe.sh is:

[[ -t 0 ]] || die "This script needs an interactive terminal (stdin is not a TTY)."

Step 9 ran the script with stdin inherited from whatever launched the suite. That only proves something when the suite happens to run without a TTY. SELF-CHECK runs in a real terminal, so stdin is a TTY, the gate correctly passes, and the script walks on to the next check — in the step's throwaway single-branch repo that is Error: No candidate branches found to merge. The following grep -q 'interactive terminal' finds nothing, set -e aborts, and the suite reports a failure against a script that behaved exactly as designed.

Measured with a real pty on stdin, not a script wrapper:

exit: 1
refuses on TTY grounds: False
output: Error: No candidate branches found to merge.

Change

One redirect. /dev/null is never a TTY, so the condition is forced rather than inherited:

"$MERGE_SCRIPT" </dev/null >/tmp/gitmerge-safe-smoke.out 2>&1 && exit 1

Verification

$ bash tests/gitmerge-safe-smoke.sh                      # no TTY
OK: gitmerge-safe safety contract passed

$ script -q /dev/null bash tests/gitmerge-safe-smoke.sh  # TTY
[9/10] non-interactive execution is refused
[10/10] TTY gate precedes network fetch
OK: gitmerge-safe safety contract passed

$ bash tools/scripts/test-all.sh
[PASS] All selftest checks passed.

The safety contract is unchanged: the script still refuses when there genuinely is no TTY, before any network operation. Step 10 still pins that the gate precedes git fetch.

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