docs: add repeat and multi-thread test (section 3.6) for the 1-thread sweep

docs/handoff/SESSION_HANDOFF.md

@@ -336,11 +336,18 @@ Validation-selected beta (seed 0) and test rare-class macro-F1 (global) afterwar
   confounded** with host (8 threads / 29 GiB documented earlier vs 12 / 48 GiB now), possibly a
   different PyTorch version (not recorded in metadata), and a different checkout path. A sign test
   (p = 0.86 / 1.0) is reported only descriptively because the pairs are not independent.
-- **Write-up:** `docs/research/SWEEP_1THREAD_SEED0_CHECK.md` (untracked, not yet committed)
-  summarizes the sweep, the run-to-run difference, the noise checks and the comparison above.
+- **Write-up:** `docs/research/SWEEP_1THREAD_SEED0_CHECK.md` (committed in `ad203eb`; section 3.6
+  was added afterwards and is uncommitted) summarizes the sweep, the grid-vs-sweep difference,
+  the noise checks and the comparison above.
+- **Repeat / multi-thread test** (`results/sweep_repro/`, X-IIoTID alpha 0.25 seed 0 beta 0 only):
+  a 1-thread repeat is bit-identical to the sweep run (all result JSON and the prototype
+  snapshot), so the 1-thread sweep has no run-to-run noise. An 8-thread run on this host differs
+  from the 1-thread run (test rare-F1 1.9e-3) and also does not reproduce the old grid (2.5e-3).
+  Thread count changes results but does not explain the whole grid-vs-sweep difference; host and
+  PyTorch version remain uncontrolled. 5G-NIDD and an 8-thread repeat were not tested.
 - **Exact next task:** decide with the user whether the 5G-NIDD alpha 0.5 / 0.75 disagreement
-  warrants investigating the thread-count hypothesis (needs extra runs; not started) and whether
-  to commit the handoff and the write-up. Do not change the primary pooled selection on the basis of this single-seed re-run.
+  warrants a 5G-NIDD repeat / multi-thread test (needs extra runs; not started) and whether to
+  commit section 3.6. Do not change the primary pooled selection on the basis of this single-seed re-run.
 - **Housekeeping:** the tmux session `sweep` still exists (windows `control`, `pool`); the
   `heartbeat` window was stopped on 2026-10-29. Backups of edited sweep scripts are `*.bak` in
   `results/sweep/`; orphaned attempt-1 artifacts are in `results/sweep/_orphans_20261027T011213Z/`.

docs/research/SWEEP_1THREAD_SEED0_CHECK.md

@@ -44,8 +44,10 @@ choice and the grid's pooled choice, using validation metrics only.
 | test rare-class macro-F1 | 0.0022 | 0.0127 (5G-NIDD, alpha 0.5, beta 0.75) |
 | validation selection metric | 0.0029 | 0.0328 |
 
-None of the 30 pairs is exactly equal. The cause is not established. Thread count is a
-hypothesis only; no experiment isolates it.
+None of the 30 pairs is exactly equal. The cause is not established (section 3.6 tests thread
+count for one configuration). Because the 1-thread setup turned out to be exactly reproducible
+(section 3.6), "run-to-run" in sections 3.1 to 3.4 means earlier grid versus 1-thread sweep: a
+difference between setups, not noise inside one setup.
 
 ### 3.2 Seed-0 selection
 
@@ -140,17 +142,46 @@ one partition), so the sign counts below are descriptive only.
   metadata stores no PyTorch version, so a library difference cannot be excluded (current:
   2.14.1+cpu). Whether the grid ran on a different machine is inferred, not verified.
 
+### 3.6 Repeat and multi-thread test (X-IIoTID alpha 0.25 seed 0 beta 0; `results/sweep_repro/`)
+
+Two extra runs of one configuration on this host: same partition (hash unchanged), same
+hyperparameters, same 11 GiB memory scope. A: 1 thread through `thread1_launcher.py`, identical
+to the sweep command (CPU 99 %, wall 9 704 s). B: 8 threads through `run_baseline.py` directly
+(CPU 758 %, wall 4 546 s). Script: `results/sweep_repro/compare_repro.py`.
+
+| pair | test rare-F1 abs diff | val selection metric abs diff | last-round rare-F1 diff | all result JSON equal | prototype snapshot byte-identical |
+|---|---|---|---|---|---|
+| A (1 thread repeat) vs sweep | 0 | 0 | 0 | yes | yes |
+| A (= sweep) vs grid | 6.2e-4 | 1.27e-3 | 3.4e-4 | no | no |
+| B (8 threads) vs A (= sweep) | 1.86e-3 | 4.6e-4 | 1.9e-3 | no | no |
+| B (8 threads) vs grid | 2.47e-3 | 8.0e-4 | 2.2e-3 | no | no |
+
+- **The 1-thread setup is exactly reproducible** (one configuration, one repeat): every compared
+  result file and the prototype snapshot of A equal the sweep run. The sweep therefore contains no
+  random run-to-run noise; the grid-vs-sweep differences are deterministic consequences of the
+  setup, not luck of a single run.
+- **Thread count changes the result.** B differs from A by 1.86e-3 on test rare-F1, the same order
+  as the median grid-vs-sweep difference (2.2e-3). One pair only.
+- **Thread count alone does not reproduce the grid.** B is not identical to the grid either. On
+  test rare-F1 it is farther from the grid (2.47e-3) than the 1-thread run is (6.2e-4); on the
+  validation metric it is slightly closer (8.0e-4 vs 1.27e-3). Host, PyTorch version and the grid's
+  exact thread count (CPU 741 to 746 % suggests about 7 to 8, not verified) remain uncontrolled.
+- **Not tested:** whether the 8-thread setup reproduces itself (needs an 8-thread repeat); any
+  other configuration, in particular 5G-NIDD, where the two beta disagreements occur. This
+  configuration's grid-vs-sweep difference (6.2e-4) is below the median over all 30 pairs, so it
+  is a favourable case for agreement and says little about the 5G-NIDD cases.
+
 ## 4. Interpretation limits
 
 - One seed. The grid pools three. Nothing here is a significance test.
 - Where the sweep and the grid disagree (5G-NIDD alpha 0.5 and 0.75), a different beta is the
   best of the tested candidates under a slightly different realization of training; this does
   not show that either beta is better.
-- Unverified: that thread count causes the run-to-run difference (it is confounded with hardware
-  and possibly library version, section 3.5). Two cheap runs would separate them: (a) repeat one
-  1-thread run and compare it bit-for-bit with the sweep run (is a repeat identical?); (b) run
-  the same configuration multi-threaded on this host and compare with the grid. Neither has
-  been run.
+- Thread count as the cause of the grid-vs-sweep difference is partly supported but not
+  established (section 3.6): threading changes the result, yet 8 threads on this host does not
+  reproduce the grid. Hardware, PyTorch version and the grid's exact thread count stay
+  uncontrolled. One configuration (X-IIoTID alpha 0.25 beta 0) was tested; an 8-thread repeat and
+  5G-NIDD were not.
 - No claim is made that support weighting improves detection, and the selected beta is "best
   among the tested candidates under the defined validation procedure", not a global optimum.
 - `S_j` handling remains the documented reproduction assumption.