feat(pfi-gx10): stage ERP-seat SFT run 3c — verified, not launched

Rehome run 3c from ana-ml2 to pfi-gx10 unchanged: same corpus, base,
recipe and hyperparameters, different host. Slower (~13.3 h vs ~2.5 h)
and correct — an Anaheim breaker trip costs a 40-minute drive each way
and 13 hosts down, three of them SureFire client machines, while the
GX10 is a ~240 W appliance at NH3 that can take nothing else down.

Verified rather than assumed, because ana-ml2 ran transformers 5.15.1
on x86-64 and this box runs 5.16.1 on aarch64 — the silent
backend-delta class that has already voided conclusions here:

  - both 49 GB base shards sha256-match ana-ml2's (size equality is a
    weaker claim and was already true)
  - a full encode was run into a throwaway dir and the encoded corpus
    compared byte-for-byte: 197,360,233 B, sha256 c08bb1fe2ecb0be3,
    identical. Every aggregate matched too. That verified artifact is
    what the run will train on — it is seeded into run-03c/encode-cache
  - the harness's own suite: 122 passed on aarch64
  - the config generator asserts key-by-key that no non-path value
    differs from run-03c.json

The encode-cache filename differs by design (base_model_path is part of
the key) — an input hash, not an output hash. Documented so it is not
misread as drift, or "fixed" by faking /tank on this box.

Corpus is copied to local NVMe; the box mounts no NFS. nh3-nas is now on
the same subnet, which makes mounting it tempting and still wrong under
a 13 h unattended run.

The launcher refuses on a live pidfile rather than a pgrep: `pgrep -f
erp_sft_harness` invoked over ssh matches the invoking shell's own argv.
That self-match cost a shell during staging.

Not launched. 13.3 h is the operator's call.

scripts/erp-tune-gx10/launch-run-03c.sh

@@ -0,0 +1,73 @@
+#!/usr/bin/env bash
+# Launch ERP-seat SFT run 3c on pfi-gx10 (NVIDIA GB10, aarch64, sm_121).
+#
+# Run this ON pfi-gx10 as infra-ops. It detaches the job from the invoking
+# shell and logs to the box, so a reaped SSH session cannot take the run with
+# it -- the failure mode that lost the first probe launch on 2026-09-01.
+#
+# Expected: 604 optimizer steps at ~79.4 s/it => ~13.3 h.
+# Checkpoints every 50 steps, ~852 MB each (~10 GB total).
+set -euo pipefail
+
+ROOT=/home/infra-ops/erp-tune
+HARNESS=$ROOT/eitri-smithy
+VENV=/home/infra-ops/ml/.venv/bin/python
+CONFIG=$ROOT/run-03c-gx10.json
+LOG=$ROOT/run-03c.log
+
+# --- Preconditions, asserted rather than assumed -----------------------------
+
+# A stuck orphan holding unified memory while PyTorch reports zero allocated
+# already doomed three relaunches on this box and got blamed on the new run
+# each time. Assert the GPU is clear.
+apps=$(nvidia-smi --query-compute-apps=pid --format=csv,noheader | tr -d '[:space:]')
+if [ -n "$apps" ]; then
+  echo "REFUSING: GPU is not clear -- compute apps still resident:" >&2
+  nvidia-smi --query-compute-apps=pid,process_name,used_memory --format=csv >&2
+  exit 1
+fi
+
+# Deliberately NOT `pgrep -f erp_sft_harness`: run this over ssh and the
+# pattern appears in the invoking shell's own argv, so the guard matches
+# itself and refuses every launch. Same self-match that makes `pkill -f`
+# unsafe over ssh. The pidfile is exact and cannot self-match; the GPU
+# assertion above catches an orphan under any name.
+if [ -f "$ROOT/run-03c.pid" ] && kill -0 "$(cat "$ROOT/run-03c.pid")" 2>/dev/null; then
+  echo "REFUSING: run-03c.pid names a live process $(cat "$ROOT/run-03c.pid"):" >&2
+  ps -p "$(cat "$ROOT/run-03c.pid")" -o pid,etime,cmd >&2
+  exit 1
+fi
+
+if [ -e "$LOG" ]; then
+  echo "REFUSING: $LOG exists. Move it aside first so two runs cannot share a log." >&2
+  exit 1
+fi
+
+for p in "$HARNESS/erp_sft_harness/__main__.py" "$VENV" "$CONFIG"; do
+  [ -e "$p" ] || { echo "REFUSING: missing $p" >&2; exit 1; }
+done
+
+# Free space for checkpoints: 12 x 852 MB + final adapter, with headroom.
+avail=$(df --output=avail -BG "$ROOT" | tail -1 | tr -dc '0-9')
+if [ "$avail" -lt 40 ]; then
+  echo "REFUSING: only ${avail}G free under $ROOT; want >=40G for checkpoints." >&2
+  exit 1
+fi
+
+# --- Launch ------------------------------------------------------------------
+
+cd "$HARNESS"
+{
+  echo "# launched $(date -Is) on $(hostname) by ${USER}"
+  echo "# harness $(git rev-parse --short HEAD) config $CONFIG"
+} > "$LOG"
+
+setsid nohup "$VENV" -m erp_sft_harness --config "$CONFIG" >> "$LOG" 2>&1 < /dev/null &
+pid=$!
+echo "$pid" > "$ROOT/run-03c.pid"
+
+echo "launched pid $pid -> $LOG"
+echo
+echo "watch:   tail -f $LOG | tr '\\r' '\\n'"
+echo "steps:   grep -ao '[0-9]*/604 \[[^]]*\]' $LOG | tail -1"
+echo "stop:    kill \$(cat $ROOT/run-03c.pid)      # by PID -- never pkill -f over ssh"