fix(qa): the Golden Output gate was asserting on a coin flip, not on correctness

[noahgift]

Closes the long-running #2350 red nightly. It is not a GPU defect — the gate picked a prompt whose greedy continuation sits on a near-tie, so it flips between backends.

Measured — one binary, one model, greedy (temperature 0.0, top_k 1), 512 tokens

prompt	CPU	CUDA
Hello	Hello! How can I assist you today?	I'm sorry, but I'm not sure what you're asking
Hi	I'm sorry, but I'm not sure what you're asking	I'm here to help! How can I assist you today?
What is 2+2?	2+2 equals 4.	2 + 2 equals 4.
Hello there, how are you doing today my friend?	Hello! I'm doing well, thank you.	same
What is the capital of France?	The capital of France is Paris.	same

Read row 2. The same evasive completion this issue is named after appears on CPU — just for Hi instead of Hello. Both backends answer bare one-word greetings evasively; they only disagree about which one tips over. Substantive prompts agree on both.

So this is small, legitimate kernel numerics — F2 measures full prefill parity at cosine 0.9937 with zero argmax mismatches — amplified by greedy decoding at a near-tie. #2323 didn't break decoding; it made the CUDA path reachable on sm_89 and the coin landed the other way.

Fix

Replace the bare greeting with two wide-margin prompts, both verified to produce identical continuations on CPU and CUDA. The gate now runs three cases instead of two — this strengthens it rather than weakening it.

Verified end-to-end on GPU with a HEAD-built binary:

✓ PASS Golden Output   3 golden test cases passed   (7.4s)
✓ ALL GATES PASSED

Ratchet

golden_prompts_are_not_bare_one_word_messages rejects any golden prompt whose user message is under three words. Word count is a crude proxy for "wide argmax margin", but it's checkable without a GPU in CI and blocks the exact shape that cost 24 days of red nightly.

Mutation-verified: reinstating "Hello" turns it RED, naming the prompt and the word count.

Also fixed: apr_bin.sh was bash-only

It derived the checkout from ${BASH_SOURCE[0]}. Sourced from zsh (the dev box's interactive shell) that is empty, so dirname "" → ., the cd .. escaped the checkout, and cargo metadata reported a different workspace's target dir — the orphaned /mnt/nvme-raid0/targets/aprender.

A resolver that silently resolves against the wrong workspace is exactly what that file exists to prevent. Now uses git rev-parse --show-toplevel: portable and worktree-correct. Verified in both shells — bash resolves the fresh binary, zsh fails closed.

Harness

Adds crates/apr-cli/tests/golden_prompt_tokenization.rs, used to reach all of the above. It also proves the embedded BPE tokenizer is clean (9 tokens, correct 151644/151645 control ids, exact round-trip), which ruled out the "gate feeds malformed text" hypothesis.

🤖 Generated with Claude Code