magic-s2000 study: reg_delay/noadaptc flags, 4-arm queue v2, redx trajectory audit

- lt_ep_train: --reg_delay N (reg-free early phase: resreg/jr/floss/adaptc off
  for first N steps) + --noadaptc (kill hidden jacreg==0 damping feedback that
  would pollute single-reg ablation arms)
- queue v2: 4 arms delay-first (abl_delay = reg-free 2k -> proven pair)
- eig_traj/2/3: ARPACK audit of redx_traj — the run crossed the edge EARLY and
  oscillated (s1000 rotating-unstable, s1400 excursion mu=+2.1 self-recovered,
  s2000 the ONLY stable snapshot mu=-0.02, s2100/s2200 already back out) =>
  s2000 is a post-excursion STABILITY-DIP capture, dip width <100 steps;
  learning survives mild instability (val fell through unstable stretches).
  lead_rho cold-40 under-reads clusters — NOT a classifier; ARPACK for audits.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014FAPDWQ49M5Ye3NpTndTpn

1 files changed, 13 insertions, 5 deletions

diff --git a/ep_run/lt_ep_train.py b/ep_run/lt_ep_train.py
index 99a1811..d56af1d 100644
--- a/ep_run/lt_ep_train.py
+++ b/ep_run/lt_ep_train.py
@@ -407,6 +407,8 @@ def main():
     ap.add_argument('--floss_q', type=int, default=10)         # unroll horizon (steps past z_T1, with graph, sub-batch)
     ap.add_argument('--floss_rho', type=float, default=0.995)  # per-step contraction target (one-sided; matches eig_margin)
     ap.add_argument('--floss_bsub', type=int, default=4)       # sub-batch rows for the graphed unroll (memory)
+    ap.add_argument('--reg_delay', type=int, default=0)        # reg-free first N steps (resreg/jacreg/floss/adaptc all off) — magic-s2000 test
+    ap.add_argument('--noadaptc', action='store_true')         # kill the hidden jacreg==0 damping feedback (clean single-reg arms)
     ap.add_argument('--diag_cos', type=int, default=0)         # #1: every N steps, log cos(EP grad, exact BPTT grad) + res
     ap.add_argument('--fingerprint', action='store_true')      # load --init_ckpt, print (res,cos,abscissa,val) fingerprint, exit
     ap.add_argument('--opt', choices=['adamw', 'lion', 'lionlars', 'sgdm', 'sgdsai'], default='adamw')
@@ -558,12 +560,18 @@ def main():
         idx, y = get_batch('train', cfg.B, cfg.T)
         if cfg.mode == 'ep':
             sw = hw_swap() if hw_on else None
-            grads, res = ep_step(blk, idx, y, cfg.T1, cfg.T2, cfg.eps, cfg.beta, jr, cfg.holo, cfg.hr,
-                                 cfg.t1max, cfg.res_est, cfg.t2sel, cfg.corr_every, cfg.res_gate, cfg.resreg,
-                                 cfg.eigreg, cfg.eig_margin, cfg.floss, cfg.floss_q, cfg.floss_rho, cfg.floss_bsub)
+            dly = step < cfg.reg_delay            # reg-free early phase (magic-ckpt hypothesis: reach the edge unleashed)
+            grads, res = ep_step(blk, idx, y, cfg.T1, cfg.T2, cfg.eps, cfg.beta, 0.0 if dly else jr,
+                                 cfg.holo, cfg.hr,
+                                 cfg.t1max, cfg.res_est, cfg.t2sel, cfg.corr_every, cfg.res_gate,
+                                 0.0 if dly else cfg.resreg,
+                                 cfg.eigreg, cfg.eig_margin, 0.0 if dly else cfg.floss,
+                                 cfg.floss_q, cfg.floss_rho, cfg.floss_bsub)
             if sw is not None:
                 hw_restore(sw)
-            if cfg.jacreg > 0:                    # continuous controller: drive residual -> res_target (smooth)
+            if dly:                               # delay phase: no controller, no damping feedback either
+                pass
+            elif cfg.jacreg > 0:                  # continuous controller: drive residual -> res_target (smooth)
                 flo = cfg.jacreg if cfg.jr_floor is None else cfg.jr_floor
                 if cfg.jr_lrcouple:
                     flo *= sched.get_last_lr()[0] / cfg.lr
@@ -573,7 +581,7 @@ def main():
                     rtgt = math.exp((1 - u) * math.log(cfg.res_target) + u * math.log(cfg.rt_final))
                 rs = res if rs is None else cfg.res_ema * rs + (1 - cfg.res_ema) * res
                 jr = min(cfg.jr_max, max(flo, jr * math.exp(0.3 * math.log((rs + 1e-9) / rtgt))))
-            else:                                 # damping feedback (no jacreg)
+            elif not cfg.noadaptc:                # damping feedback (no jacreg) — DISABLE for clean single-reg ablations
                 if res > 1e-3:
                     blk.c = min(cfg.ccap, blk.c * 1.3)
                 elif res < 2e-4: