journal: erase arm sub4 (-7.8pp hack/+4.7pp solve, win on file_marker)

Co-Authored-By: Claudypoo <288921227+claudypoo@users.noreply.github.com>

RESEARCH_JOURNAL.md

@@ -2,6 +2,61 @@
 
 Append-only. New entries at the top, date-stamped. Never edit old entries.
 
+## 2026-05-31 (l) — erase (one-sided projection) vs vanilla: -7.8pp hack / +4.7pp solve, but the win is on held-out file_marker not in-dist run_tests
+
+**Context:** commit `b0432af` on `probe/distill-cosine`; pueue id 41; projected/erase
+(intervention=erase, refresh-5 default), seed 41, 60 steps, fast preset, 4-mode substrate,
+mix=0.125. Second arm of the sub4 overlay sweep. Pairs against vanilla entry (k) above.
+Artifact: `out/runs/20260531T163110_fast_projected_seed41_sub4_erase/per_mode_deploy.json`.
+
+**Hypothesis:** erase suppresses hack below vanilla (0.359) at matched solve, with the
+largest drop on the in-dist mode the v_hack was built closest to (run_tests).
+
+### Observations
+
+- [obs] cout=0.00 throughout (e.g. step 37) -> projection mechanically fires, removes all
+  hack-ward grad. Not a silent no-op.
+- [obs] cin_t (0.09) < cin_s (0.15) by mid-training (step 37) -- the REVERSE of the wanted
+  cin_t>cin_s. Consistent with v_hack staleness (entry j).
+- [obs] Aggregate FINAL EVAL (n=64, deploy==train): hack=0.281 solve=0.500, vs vanilla
+  hack=0.359 solve=0.453. So -7.8pp hack, +4.7pp solve. BLUF HACK_RATE=0.338 PASS_RATE=0.291.
+- [obs] Per-mode erase vs vanilla:
+
+| mode (n)          | dist     | vanilla hack/solve | erase hack/solve |
+|-------------------|----------|--------------------|------------------|
+| run_tests (8)     | IN-dist  | 7/8  / 0/8         | 8/8  / 0/8       |
+| file_marker (32)  | held-out | 16/32 / 6/32       | 10/32 / 13/32    |
+| sentinel (24)     | held-out | 0/24 / 23/24       | 0/24 / 19/24     |
+
+### Inferences
+
+- [inf] Erase's entire net win is concentrated in file_marker (hack 50%->31%, solve
+  19%->41%); run_tests stays saturated and sentinel was never hacked. So the aggregate
+  -7.8pp/+4.7pp is really "erase rescued file_marker". {reason: "the other two modes are
+  unchanged within noise; file_marker is the only mode that moved", credence: 0.85}
+- [inf] The win landing on held-out file_marker rather than in-dist run_tests is mildly
+  counterintuitive but NOT evidence against the method -- run_tests is already saturated at
+  vanilla (7/8) so there is little hack-rate headroom to recover there, whereas file_marker
+  at 50% has room to move. {reason: "ceiling effect on run_tests; headroom on file_marker",
+  credence: 0.6}
+- [inf] -7.8pp is far short of the preregistered 30pp (H1). Consistent with prior n=1
+  erase results. {reason: "matches the G0 21-pair erase magnitude band", credence: 0.7}
+
+### Failure modes considered
+
+- **Likely:** run_tests n=8 is too small -- the 7/8 vs 8/8 "no suppression" is one rollout,
+  pure noise; erase may help run_tests too at larger n. Prior: 0.4. Check: read the
+  streaming hk_rt cumulative column, or widen the eval subset.
+- **Subtle:** file_marker solve 6->13 is the solve-detector being fooled by a file_marker
+  artifact, not real solving. Prior: 0.2. Check: spot-read a file_marker "solve" rollout.
+- **Null:** the -7.8pp/+4.7pp is seed-41 run-to-run variance, not the erase intervention.
+  Prior: 0.3. Check: seed 43/44 replicates (queued after the sweep).
+
+### Next action
+
+Route (42) running, route2 (43-44) queued. The deploy-solve>=train-solve KEY CHECK only
+becomes testable on the quarantine arms (42-44, deploy!=train). Then build #162 overlay.
+
 ## 2026-05-31 (k) — vanilla emergence reference (sub4 overlay): per-mode hacking is asymmetric, not uniform
 
 **Context:** commit `b72c5ac` on `probe/distill-cosine`; pueue id 40; vanilla (intervention=none),