spec2.md records:
- Phase 1 result (NLL cos signal +0.747 pure-hack vs +0.398 mixed)
- Phase 2: mixed-replay GRPO probe, partial impl
- Phase 3: $400/65h sweep, predicated on Phase 2 cos_in signal
User correction mid-implementation: Phase 2 and Phase 3 should share
train.py code with different --steps, not build separate replay
machinery. Mixed-replay refactor in probe_distill.py is left wired
in (replay_dirs, loss_mode, save_step_slim, heterogeneous plen
loader) but marked TODO for completion; canonical Phase 2 path is
train.py at smaller scale.
probe_distill.py gets --base-only mode and load_problems_base for the
non-hack pool, used as one half of the variance source.
Also addresses user complaint "don't save replayed batches" with
save_step_slim that drops the duplicated prompts/completions in
favour of cosine-only annotations.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Reviewer flagged 4 killer flaws: behaviour-policy logp mismatch on
teacher rows (ratio pegs to clip from step 0), frac_clipped not
ratio_mean is the saturation diagnostic, mixed-policy can produce
gradient AWAY from hacking when teacher-half has zero adv variance,
and probe_distill NLL normalizer is incomparable to train.py Dr.GRPO.
User instruction reinforces: no mixed policy. Stay with hacky teacher
+ student NLL distill (existing Phase 1 pipeline, UAT 4/4).
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
R1-R4 (Phase 1) marked done with evidence pointers to
out/probe_distill/{teacher_pool,vanilla_seed41,projected_seed41}/.
R5 = GRPO trajectory probe (mixed-policy generator to restore reward
variance). R6 = LoRA-vs-SVD arm comparison. R7 = GRPO-contrastive
v_hack re-extraction (fallback only).
Errors table records the two diagnosis/fix loops from Phase 1: the
prompt-distribution mismatch and the zero-advantage skip.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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