feat: codex-run.sh watchdog wrapper + stub tests

tests/test-run.sh

@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+set -eu
+HERE=$(cd "$(dirname "$0")" && pwd)
+RUN=$HERE/../scripts/codex-run.sh
+TMP=$(mktemp -d)
+trap 'rm -rf "$TMP"' EXIT
+
+# 1. happy path -> status ok, thread_id captured, exit 0
+CODEX_BIN=$HERE/stub-ok/codex "$RUN" "$TMP/ok" exec "hello"
+[[ $(cat "$TMP/ok/status") == ok ]]
+[[ $(cat "$TMP/ok/thread_id") == test-thread-123 ]]
+[[ $(cat "$TMP/ok/last.md") == "stub answer" ]]
+
+# 2. stall -> watchdog kills, status stalled, exit nonzero
+if CODEX_BIN=$HERE/stub-hang/codex CODEX_STALL_TIMEOUT=4 CODEX_WATCH_INTERVAL=2 \
+   "$RUN" "$TMP/hang" exec "hello"; then
+  echo "FAIL: stall run must exit nonzero"; exit 1
+fi
+[[ $(cat "$TMP/hang/status") == stalled ]]
+[[ $(cat "$TMP/hang/thread_id") == hang-thread-456 ]]
+
+# 3. prompt.md via stdin path
+mkdir -p "$TMP/stdin"; echo "prompt from file" > "$TMP/stdin/prompt.md"
+CODEX_BIN=$HERE/stub-ok/codex "$RUN" "$TMP/stdin" exec
+[[ $(cat "$TMP/stdin/status") == ok ]]
+
+echo "ALL PASS"