ab-v3 left 36 ark empty + 15 timeout + 4 429 + 6 deepseek empty + 4
minimax timeout AFTER the existing retries=1 fired 88 times. Linear
backoff 250ms*(attempt+1) was too tight when stepping up to
retries=2 (500ms then 750ms isn't a typical Ark recovery window).
Switches to exponential 250ms*4^attempt — 250 / 1000 / 4000ms
spacing — and bumps ark + deepseek to retries=2. minimax opts in to
retries=1 (its 4 errors were wall-clock timeouts, not the model's
<think> truncation that retry can't fix anyway).
10 existing retry tests still pass; the retries=2 case now sleeps
1.25s instead of 0.75s, still well under vitest's default timeout.
ab-v3 succeeds ab-v1 (frozen 2026-04-28). Carries forward all 40
v1 obvious yaml files unchanged so the v1↔v3 overlap stays
comparable, then layers in two new dimensions.
**1. Token cost.** All clients (openai-compat, ark, bailian,
deepseek, minimax, codex-cli, stub-model) now return a
`ChatCallResult { content, usage }` instead of bare string.
Provider usage stats (`prompt_tokens` / `completion_tokens`) plumb
through realModelCall → run.ts → scoreRun → ScoreRow.{prompt,completion}Tokens.
aggregate adds avgPromptTokens{Baseline,Treatment} +
avgCompletionTokens{Baseline,Treatment} per ModelSummary.
write-report emits a new "Token cost" table with Δ columns so
narrow-tools-saves-tokens (the ab-v2 hypothesis) is measurable.
avgUsage skips rows with 0/0 usage so codex-cli (CLI doesn't
surface tokens) and harness errors don't deflate the average to
near-zero — they show '—' instead.
**2. Composite difficulty.** New 'composite' value alongside
obvious / optional. Composite prompts express multi-tool intents
where no single expected_tool_if_any applies. classifyRouting
routes composite-treatment runs into multi-tool / fallback /
garbage (3-bucket sum to 1, distinct from obvious's 4-bucket
right/wrong/fallback/garbage). aggregate adds m6_multi_tool +
m6_fallback + m6_garbage; write-report emits a "Composite routing"
table that gracefully degrades to a placeholder when no composite
yaml exists yet.
Harness side: scripts/ab-corpus/run.ts accepts --corpus ab-v3
(enum + parseArgs guard); dry-run on the v1-mirror corpus produces
a 160-row report including populated token table.
Tests: 4 new aggregate cases (composite, token avg with skip-zero,
NaN-when-no-data) + 4 new score-run cases (composite routing
multi-tool/fallback/garbage/baseline-n/a) + 2 new score-run cases
(usage plumbing) + 2 new openai-compat cases (usage parsing,
missing-usage fallback). Existing 5 retry tests updated for new
return shape. 3727 → 3740 vitest tests, all green; tsc + format
clean.
Token-cost docs and composite docs go straight into types.ts /
score-run.ts / aggregate.ts JSDoc — keeps the contract close to
the code that owns it.
ab-v2 (2026-04-28) saw kimi-k2.6 garbage rate hit 17.5% — every
failure was Ark returning empty `choices[0].message.content` or
hitting the 120s wall clock, not a model-quality issue (the model
itself routed to the right element tool 80% of the time when it
did respond). Same pattern at 7.5% on deepseek-v4-pro.
Adds optional `retries` to `callOpenAICompat` with a transient-error
allowlist: empty content, abort/timeout, HTTP 5xx, HTTP 429. Linear
250ms × (attempt+1) backoff. HTTP 4xx other than 429 stays fatal so
auth/bad-request failures don't burn retry budget.
Wires `retries: 1` through clients/ark.ts and clients/deepseek.ts.
MiniMax + Bailian + Codex stay untouched — their ab-v2 failures
were model-quality (DSL escape errors, output truncation), where
retry wastes a call without changing the outcome.
Adds an 8-case fixture in scripts/ab-corpus/clients/__tests__/ that
mocks fetch to verify: first-try success, empty-then-success,
5xx-then-success, 429-then-success, 401 fatal, retries-default-zero,
retries exhausted, and retries=2 (3 attempts total). Extends the
apps/web vitest include glob to pick up scripts/**/__tests__/.
DeepSeek wasn't in the harness; A/B v2 needed it for the 5-model run.
api.deepseek.com is OpenAI-compatible, so the client mirrors the
minimax pattern (callOpenAICompat with DEEPSEEK_API_KEY env, override-
able DEEPSEEK_BASE_URL).
Router: /^deepseek/i routes to the new client. Aliases `deepseek` /
`deepseek-pro` resolve to `deepseek-v4-pro` (current flagship per
docs); `deepseek-v4-flash` and the deprecated `deepseek-chat` /
`deepseek-reasoner` ids pass through verbatim until the 2026-07-24
sunset upstream.
Verified live with mobile-bio-textarea smoke (B emits batch_design,
T emits add_textarea_v0). Full ab-v2 results across all 5 models in
docs/notes/2026-04-28-ab-v2-results.md.
