grader bug fix + ref reward semantics + Qwen3-4B substrate

Three independent issues that together made every prior `gt=0` measurement
bogus and the H4 hypothesis untestable:

1. Grader bug: rewards.py wrapped already-asserted gt tests with `assert (...)`
   producing `assert (assert ...)` SyntaxErrors. Every gt_pass was False
   regardless of correctness. Fixed by joining tests verbatim.

2. Reward semantics: matched reference `CorrectOrHintedCompileCode(allow_hint=True)`
   default (docs/vendor/rl-rewardhacking/src/train/rewards.py:161). Format
   paid on can_compile; correctness paid on `gt_pass OR hacked`. Magnitudes
   0.5/3.0 (was 0.25/1.0). The reference's run_no_intervention (main RL run)
   uses these defaults; ours was effectively the run_rl_baseline control.

3. Substrate: full preset repointed to Qwen/Qwen3-4B (reference's
   DEFAULT_MODEL_ID). Peaks 72.78GB at G=12/max_new=1024 on 96GB. Faster
   wall-time than 2B (35s vs 126s/step) because 4B writes shorter solutions.
   beta=1e-3 (was 0.04) per reference config.py:135.

Also: ref `pass_test` + `BASE_FORMAT_SYSTEM_PROMPT` injected via load_problems
(was dataset's baked-in CODE_SYSTEM_PROMPT which is the control prompt);
token-efficient logging (loguru single-char icons through tqdm.write, verbose
log to logs/, FIRST BATCH dump → DEBUG, per-step diag → DEBUG, final tail with
cue emoji + TSV table); docs/vendor/ clones of rl-rewardhacking and simple_GRPO
for greppable side-by-side; new RESEARCH_JOURNAL.md.

First-run 4B vanilla 5-step post-fix: PASS_RATE=0.558, HACK_RATE=0.000,
rew_std~1.5, loss alive. Substrate is competent at medhard LeetCode.

200-step gated probe queued via pueue (tasks 91→92→93→94 with --after deps):
extract-vhack-full → verify-vhack-full → vanilla seed 41 → projected seed 41.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

README.md

@@ -19,10 +19,14 @@ uv sync
 just fast-dev-run        # tiny-random model, ~1-2 min, real pipeline end-to-end
 just smoke-vanilla       # vanilla pathway smoke
 just smoke-projected     # projected pathway smoke
-just download-model      # warm Qwen3.5-2B cache (then real runs need 96GB GPU)
-just queue               # queue all sweep arms via pueue (on the GPU box)
+just download-model      # warm Qwen3-4B cache (full preset peaks ~73GB on 96GB)
+just queue-full          # queue extract + 3-seed vanilla + 3-seed projected sweep
 ```
 
+See [RESEARCH_JOURNAL.md](RESEARCH_JOURNAL.md) for session-by-session findings,
+including the 2026-05-23 grader-bug discovery that invalidated all prior `gt=0`
+measurements and the move from Qwen3.5-2B to Qwen3-4B (reference substrate).
+
 ## Hypotheses (preregistered)
 
 See [spec.md](spec.md). Headline: H1 — gradient projection in SVD basis against