# std79 DoE — 3(architecture) × 9(identity) × 3(replicate) randomized full-factorial

The formal successor to `experiments/std79-exerciser/`'s ad hoc campaign (see FABRIC-3.md §XII),
requested as a genuine randomized full-factorial design matching this project's own DoE
methodology (`capsules/doe.4th`'s Fisher-Yates run-matrix shuffle) rather than convenience
batching — and written entirely in FORTH, not host-orchestrated shell scripting. See
FABRIC-3.md §XV for the design writeup and §XVI for the real aarch64 Stadium/COOL scaling bug
that was found, root-caused, and fixed (`src/starkernel/vm/stadium.c`, commit pending) — the
3-boot batching workaround below is now historical only; a single boot with all 9 identities
simultaneously live works cleanly on all three architectures as of the fix.

`std79-doe.fth` is not a capsule loaded via `EXEC` — feed it as raw text to a running REPL
(e.g. `socat - UNIX-CONNECT:<serial_sock> < std79-doe.fth`), same as the original exerciser, then
invoke `EXEC-STD79-DOE ( seed lo hi -- )` once loaded. `lo`/`hi` select which identity-index
range (0-8) this boot's live VMs cover — pass `0 8` for a single boot with all 9 identities
simultaneously attached (now confirmed working on all three architectures, see §XVI); a narrower
range (e.g. `0 2`, `3 5`, `6 8`) still works too, for running the DoE across multiple smaller
boots if ever needed for an unrelated reason. Every boot must use the *same* seed so
`INIT-MATRIX`/`SHUFFLE-MATRIX` reproduce the identical 27-slot master permutation; only the
`lo`/`hi` filter differs, so `run_id` (always the slot's true position in the master shuffle,
0-26) stays directly comparable across boots.

`results-20260911/` holds the raw captured serial output from the *original* campaign (pre-fix):
`amd64-doe-raw.log` (all 27 trials, one boot, all 9 identities simultaneously live) and
`{aarch64,riscv64}-doe-batch{1,2,3}-raw.log` (27 trials each, split across 3 boots of 3
identities, the then-necessary workaround). **Result: 81/81 trials correct, 0 mismatches.**

`results-20260911-stadium-fix/` holds the *post-fix* rerun — one boot per architecture, all 9
identities simultaneously live in every boot, same seed throughout. **Result: 81/81 trials
correct, 0 mismatches, byte-identical output to the original campaign** — and the DOE-RUN
header sequence (run_id/id_idx/id_label/rep assignment) is md5-identical across all three raw
logs, confirming the master shuffle is genuinely architecture-independent. Total per-architecture
wall-clock (boot + all 9 identity attaches + full 27-trial run, one continuous QEMU session):
amd64 ~165s, aarch64 ~290s, riscv64 ~161s — aarch64's identity 04 attach alone, which stalled
90+ minutes before the fix, now completes in ~34s.