review(5): §4 cron T0 MISS — busybox crond non-functional as non-root (A5-7 OPEN)

Cold-verified at 23:11Z: T0 (23:04Z) was missed; no upgrader-cron.log created.
busybox crond with -c dir requires root for setuid; silently skips all jobs as
non-root 'loops' user. Confirmed by both T0 miss and a * * * * * control probe
(waited through 23:09+23:10, nothing fired).

V9 PASS stands. Gate M5 remains open pending a working cron mechanism + re-fire.
A5-7 filed in BACKLOG-5. BUILDER-INBOX sent.

machine-docs/BACKLOG-5.md

@@ -26,6 +26,56 @@ Single-writer: `## Build backlog` = Builder-only; `## Adversary findings` = Adve
 
 ## Adversary findings
 
+### [adversary] A5-7 — §4 cron: busybox crond does NOT execute jobs as non-root user
+**Status:** OPEN — found 2026-06-01T23:11Z
+
+The §4 weekly cron was installed using busybox crond in a tmux session, invoked with:
+```
+crond -f -d 5 -c /home/loops/.cc-ci-crontabs -L /srv/cc-ci/.cc-ci-logs/crond.log
+```
+The crontab file `/home/loops/.cc-ci-crontabs/loops` contains the correct schedule (`4 23 * * 1`).
+
+**Finding: crond never executes any job.**
+
+Cold-verified T0 miss at 23:04Z (2 minutes after T0):
+- `/srv/cc-ci/.cc-ci-logs/upgrader-cron.log` does NOT exist.
+- crond.log shows only 3 startup lines; last modified 22:08:44 UTC — no entries after startup.
+- No cc-ci-upgrader session started at 23:04Z (`python3 launch-upgrader.py status` → stopped).
+
+Cold-verified with `* * * * *` test entry (every-minute control):
+- Added `* * * * * date -u >> /tmp/cc-ci-crond-test.log 2>&1` to the crontab.
+- Waited through 23:09 and 23:10 UTC — no `/tmp/cc-ci-crond-test.log` created.
+- Confirmed: busybox crond is completely ignoring ALL cron entries.
+
+**Root cause:** busybox crond's `-c dir` mode is designed to run as root. It reads each file in
+the directory as a per-user crontab (filename = username). Before executing a job, it calls
+`setgid(pw->pw_gid)` + `setuid(pw->pw_uid)`. Running as non-root user `loops`, `setgid/setuid`
+fail with EPERM, so crond silently skips all jobs.
+
+**Impact:** The §4 weekly cron is completely non-functional. T0 (23:04 UTC) was missed.
+The plan's §4 requirement ("verify the cron-equivalent path end-to-end; confirm real first fire
+at T0") is NOT met.
+
+**Required fix:** Replace busybox crond with a mechanism that works as a non-root user. Options
+per plan §4:
+1. **Claude scheduled task** (`/schedule` skill → `CronCreate` harness tool): built-in, no root
+   needed, tested mechanism.
+2. **systemd user timer** (`systemctl --user enable/start cc-ci-upgrader.timer`): requires writing
+   a user service unit file to `~/.config/systemd/user/`.
+3. **`at` one-off for T0**: doesn't provide recurring weekly schedule.
+
+**Cold repro:**
+1. `ssh loops@<orch> 'cat /srv/cc-ci/.cc-ci-logs/upgrader-cron.log 2>/dev/null || echo "(no log)"'`
+   → "(no log)"
+2. `ssh loops@<orch> 'stat /srv/cc-ci/.cc-ci-logs/crond.log | grep Modify'`
+   → Modify: 2026-06-01 22:08:44 (no update after crond start)
+3. `ssh loops@<orch> 'python3 /srv/cc-ci/cc-ci-plan/launch-upgrader.py status'`
+   → "stopped"
+
+(Only Adversary closes this after re-test with a working T0 fire.)
+
+---
+
 ### [adversary] A5-5 — V5: explanatory comment references wrong build/failures; no RESULT: SUCCESS-PENDING-TESTS
 **Status:** CLOSED — re-tested 2026-06-01T21:49Z; see `REVIEW-5.md` follow-up entry.
 ORIGINALLY OPEN — found 2026-06-01T21:38Z