libtest with --test-threads=1 (the documented invariant for this file's DDP
tests) runs tests alphabetically. The new
proc_per_gpu_dropout_is_live_and_p0_matches_no_dropout ('d') runs BEFORE
proc_per_gpu_matches_single_gpu_and_thread_path ('m'). It sets ENV_DROPOUT=0.2
via std::env::set_var; if left in place, the correctness test's spawned workers
would inherit it (Command inherits parent env by default) and build with
cfg.dropout=0.2 while its single-GPU baseline (run_single_gpu → test_config →
dropout=0) stays at 0 — GATE (a) `max_rel_single < 1e-3` would blow up by
orders of magnitude.
Two defenses:
- correctness test remove_var(ENV_DROPOUT) before spawn (belt): even if the
dropout test forgot to clean up, this test starts from a clean env.
- dropout test remove_var(ENV_DROPOUT, ENV_DUMP_DIR) at exit (suspenders):
keep the invariant "each test leaves the env as it found it" so any future
test added after these two starts clean too.
Same --test-threads=1 SAFETY comment applies (no concurrent env access).
Analogue of the ddp_dropout_is_live_and_p0_bit_identical test (T21, thread-per-
GPU) for the process-per-GPU launcher. Runs launch_processes twice on the same
corpus / init / config with the ONLY difference being cfg.dropout (passed
launcher→worker via a new XTRAIN_TEST_DROPOUT env — worker re-execs cannot
inherit argv changes), reads rank 0's loss trajectory from both runs, and
asserts GATE B: max |loss diff| > 1e-3.
The threshold sits ~4 orders of magnitude above this box's KI-5 cross-rank NCCL
noise floor (~1e-7), so it is an unambiguous "dropout mask is applied" signal,
not a noise measurement. Pre-fix (missing cfg.dropout = ... in the worker /
launcher, exactly the gap the paired launcher commit closes) both traces are
bit-identical and this test FAILs.
Also wires ENV_DROPOUT into the shared worker entry so the existing correctness
test's contract is unchanged (absent env → 0.0 → same synth run as before).
p0/ and p02/ subdirs isolate the two invocations' dumps.
Enable assistant-only supervised fine-tuning and a fixed chat-prompt eval path
used by the v12 SFT runs:
- cross_entropy ignores negative targets (-100 ignore-index), normalizing by
valid rows instead of all rows; CUDA fwd/bwd skip t<0 (ops.rs, nn.cu).
- Corpus gains optional labels + load_sft_tsv_cached: two-column TSV is
formatted as 'User: .. \nAssistant:' + answer + <|endoftext|>, prompt tokens
masked to -100 while answer+EOS are supervised; i32 label cache alongside the
u16 token cache; sample() retries windows that are fully masked; eval uses
target_window so masking applies to val loss too (data.rs, train_loop.rs).
- train + train_ddp: --sft-tsv selects the TSV loader, --init-ckpt continues
training from a base checkpoint.
- greedy_sample: --prompts-file/--prompt/--temperature for fixed chat-prompt
generation eval.
Test fixtures updated for the new Corpus.labels field; dropout.rs carries
incidental rustfmt. Not rebuilt locally (no CUDA toolchain on this checkout);
correctness rests on the documented v12 base+SFT runs on the GPU box.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
