[security] test-wrapper-mcp-error.sh predictable /tmp/stderr-$$.log temp file (symlink attack vector)

[kiki830621]

Problem

test-wrapper-mcp-error.sh:144, 146, 194, 196 redirects stderr to /tmp/stderr-$$.log. On shared filesystems, attacker pre-creates /tmp/stderr-12345.log as symlink to ~/.ssh/authorized_keys — 2> follows symlink, overwrites target.

Surfaced by Security Reviewer (F1 LOW), Codex (P3 #6).

Risk

• Single-user macOS dev: zero
• Shared CI/jump host: genuine TOCTOU

Expected

Use existing $TMPDIR (already mktemp -d):

ERRLOG="$TMPDIR/stderr.log"
STDOUT=$("$FAKE_WRAPPER" < /dev/null 2>"$ERRLOG")

trap cleans up.

Priority

P3 — LOW for current dev context. Harden before CI.

Source: surfaced during /idd-verify che-msg#31 (sister bug from verify ensemble — Codex + Devil's Advocate flagged convergently)

Verify report: #90 (comment)
Related issue: PsychQuant/che-msg#31
Related PR: psychquant-claude-plugins#90 (PR-1 ships v1.3.2)

🤖 Filed by /idd-verify Step 5b follow-up triage.