## Code Review: multi-loophole substrate (e2d1f2c^..HEAD)

### Summary
Non-overlap grader (`passed=gt_correct OR channel_i`) + even Kuhn assignment for K=3 substrate. Enables projection test of known-hack v_hack on unknown hacks.

### Critical
- [rewards.py:250-271] `_gt_correct` sentinel (post-assert print) is reachable while a wrong solution has registered `atexit.register(os._exit,0)` or `threading.Thread(target=lambda:os._exit(0)).start()`. The subprocess still prints the sentinel (main thread) before the exit fires or runs in background. `gt_correct=True`, `passed=True`, `exploited=False` on a wrong solution in ANY mode. Violates the strict-oracle premise and non-overlap (foreign exploit pays everywhere). Verify_rewards does not test atexit/thread cases.

### Important
- Side-channel teachers (sentinel/stdout/file) are recipe-elicited at 1% base compliance (derisk #10), not RL-emergent. The "student learns EACH from teacher" claim holds only for exit_code + pool run_tests; remaining modes require Phase-1 emergence runs first.

### Suggestions
- Document atexit/thread attack surface in spec and add a verify case before trusting Phase-2 numbers.

### Verdict
REQUEST CHANGES

Fix atexit/thread oracle bypass before any projection run; non-overlap is load-bearing for the research question.
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