docs+chore: out/ reorg scheme (queue-gated) + archive dead _OLD_step_format dirs

out/ is 25GB/195 loose files. Target: one subdir per datatype, per-run
artifacts under runs/<ts>_<slug>/. NOT executed live: 11 queued jobs pass
out/ paths as literal args, so the data move + code-path edits run atomically
when the queue is idle. Archived the unreferenced *_OLD_step_format dirs now.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docs/spec/20260530_out_dir_reorg.md

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+# out/ reorg — clean path scheme (by datatype, run-prefixed)
+
+## Goal
+out/ is 25GB / 195 loose files: `train_*.safetensors` checkpoints, `v_hack_*`,
+`vhack_grads_*`, and a dozen `probe_distill/teacher_pool*` dirs all at top level.
+Sort by path: one subdir per datatype, per-run artifacts grouped under a
+`<timestamp>_<slug>` run dir. Code reads+writes the new paths; old outputs moved.
+
+## Why this is NOT done live (the gate)
+11 queued/running pueue jobs pass `out/` paths as literal args
+(`--v-hack-path=out/v_hack_*.safetensors`, `--teacher-pool-dir=out/probe_distill/teacher_pool`,
+`--pairs-from-pool=out/pairsets/*.json`). Moving those files mid-queue breaks
+every job that hasn't started. So the data move + code-path edits run as ONE
+atomic change when the queue is idle (`pueue status` all Done/Queued-empty).
+Until then only the unreferenced `*_OLD_step_format` dirs are archived (done
+2026-05-30 -> `out/_archive/`).
+
+## Target scheme
+```
+out/
+  vhack/        v_hack_*.safetensors            # extracted bases (flat, named)
+  vhack_grads/  vhack_grads_*.safetensors       # raw per-pair grads (extract intermediates)
+  pools/        <pool_name>/                     # teacher pools (was probe_distill/teacher_pool*)
+  pairsets/     *.json                           # unchanged
+  baked/        <variant>/                       # unchanged
+  runs/<ts>_<slug>/  train.safetensors, first_hack.safetensors   # per-train-run
+  _archive/     dead / superseded
+```
+- `runs/<ts>_<slug>/`: checkpoints currently are `out/train_<tag>.safetensors`
+  with no timestamp. Migration maps each to its log's `<ts>` via the matching
+  `logs/<ts>_*_<tag>.log`, groups into a run dir. New runs write here directly.
+- `pools/`: drop the `probe_distill/` nesting (it was never about probes);
+  flatten `teacher_pool`, `base_pool`, `mixed_*`, the `teacher_pool_rl-*` and
+  `teacher_pool_inoc-*` variants into `pools/<name>/`.
+
+## Code edits (apply atomically with the data move)
+- `train.py`: checkpoint save path -> `out/runs/<run_id>/{train,first_hack}.safetensors`
+  (`run_id` already built for the log name). `--teacher-pool-dir` default ->
+  `out/pools/teacher_pool`. v_hack load path is an explicit arg (no default).
+- `extract_vhack_grad.py`: `--out-path` default -> `out/vhack/<name>.safetensors`;
+  `--train-grads-path` default -> `out/vhack_grads/<name>.safetensors`.
+- `probe_distill.py`: pool write dir -> `out/pools/<name>`.
+- `justfile`: every recipe with `out/v_hack_*`, `out/probe_distill/teacher_pool*`,
+  `out/pairsets/*` -> new paths. (These are the literal strings the queue
+  captured, hence the idle-gate.)
+- `scripts/results.py`: `vhack=grab(r"v-hack-path=out/(\S+?)\.safetensors")` ->
+  allow the `vhack/` prefix (strip dir for the display name).
+- `scripts/plot_dynamics.py`: same v_hack path parse if it reads one.
+
+## Migration (data move, run when idle)
+A `--dry-run`-default script that: (1) `mkdir` the new dirs; (2) `git mv`/`mv`
+loose `v_hack_*`->`vhack/`, `vhack_grads_*`->`vhack_grads/`; (3) for each
+`train_*.safetensors`, find its log `<ts>` and move to `runs/<ts>_<slug>/`;
+(4) move `probe_distill/*pool*`->`pools/`. Idempotent; logs anything it can't
+map (stays put, flagged) rather than silently dropping.
+
+## Verify
+- `just smoke` + `just smoke-vanilla` green (walks write paths).
+- `just results` still parses every run (vhack display names unchanged).
+- `find out -maxdepth 1 -type f | wc -l` ~ 0 (no loose top-level files).
+- A re-extract + a fast run write into `vhack/` and `runs/` respectively.
+
+## UAT
+"out/ has one subdir per datatype; train artifacts live under runs/<ts>_<slug>/;
+nothing loose at top level; smoke + results + a fresh run all still work."