Document bad-start robustness suite

docs/harness-ablation/bad-start-robustness-suite-20260626.md

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+# Bad-start robustness suite - 2026-06-26
+
+本文定义 P0 bad-start robustness 的分布级验证。它不是新的 claim 结果，而是下一轮实验的
+pre-registration：先固定 starts、指标和 pass/fail，再运行，避免根据单个 case 调规则。
+
+## 当前前提
+
+已完成的代码 gate：
+
+- normalized full-config signature；
+- materialized effective signature：runtime-only proposal 先继承 incumbent topology 再签名；
+- CLI hard-veto：LLM/manual/harness proposal 在进入 trial 前禁止重复 effective config；
+- CandidateSet audit：`candidate_set_hash`、eligible/blocked candidates、blocked reason summary；
+- sidecar persistence：`harness/candidate-set-*.json`。
+
+已通过的单 case：
+
+```text
+TP8, DP1, gmu0.5, max-num-seqs8
+  -> TP4
+  -> TP4 + gmu0.9
+```
+
+这个 case 只能证明 sentinel recovery，不能证明分布级 robustness。
+
+## 实验矩阵
+
+使用同一 Qwen30B-A3B community vLLM 0.20 bounded replay setup、no-LLM harness、
+`search.auto_high.enabled=true`。先跑 fresh trusted-start control，得到同 commit 下的
+参考值 `R_ref`。
+
+| Group | N | Initial starts | 证明点 |
+| --- | ---: | --- | --- |
+| trusted control | 1 | 可信/default start | 定义 `R_ref` |
+| topology-only | 4 | `(TP,DP)=(8,1),(4,2),(1,4),(2,4)`，runtime nominal | 证明不是只会 `TP8 -> TP4` |
+| runtime-only | 4 | `TP2/DP1` with `gmu={0.50,0.70}` and `max-num-seqs={8,16}` | 证明 runtime floor/admission recovery |
+| combined | 4 | `TP8/gmu0.70/mns16`, `TP4/DP2/gmu0.50/mns8`, `TP1/DP8/gmu0.50/mns16`, `TP2/DP4/gmu0.70/mns8` | 证明 operators 可串联 |
+| held-out random | 8 | fixed-seed stratified samples over legal topology x low/nominal `gmu` x low/normal `mns`，排除已通过 sentinel | overfit denominator |
+
+总计：1 control + 20 novel bad starts。
+
+## Primary metrics
+
+- best-so-far SLO-feasible `req/s/GPU / R_ref`；
+- time-to-95%-reference；
+- normalized AUC over trial budget；
+- final pass rate；
+- executed normalized full-config repeat count；
+- no-op blocked count；
+- candidate family / operator sequence；
+- stop reason and `candidate_set_hash`。
+
+每个 run 必须保留：
+
+```text
+state.json
+proposals/*.json
+harness/candidate-set-*.json
+trials/trial-*/trial_spec.json
+trials/trial-*/result.json
+```
+
+## Pass/fail
+
+Run-level pass：
+
+```text
+best_so_far_req_per_gpu >= 0.95 * R_ref within 12 measured trials
+pass_rate >= 0.95
+executed_effective_config_repeat_count == 0
+no harness stop while high-priority eligible candidates remain
+```
+
+Suite-level pass：
+
+```text
+20 / 20 novel bad starts pass.
+```
+
+如果任一 novel start 失败，不能 claim distribution-level bad-start robustness。修复后必须
+冻结失败分析，并重新抽 held-out random set。
+
+## Overfit guards
+
+- pre-register all starts and random seed；
+- 不把已通过的 exact `TP8,gmu0.5,mns8` sentinel 计入 20-case denominator；
+- 不在 starts 之间调 threshold；
+- 报告 operator names，例如 `topology_bracket`, `topology_redistribute`,
+  `runtime_floor_jump`, `admission_recovery`，而不是 case-specific action；
+- 每次 stop 必须引用 `candidate_set_hash` 和 no high-priority eligible candidate evidence。
+
+## GPU cost
+
+Expected：
+
+```text
+21 runs * 6-8 measured trials = 126-168 trials
+```
+
+Hard cap：
+
+```text
+21 runs * 12 measured trials = 252 trials
+```
+
+按当前 Qwen30B bounded replay 粗估：
+
+```text
+15-35 min / measured trial
+expected = 250-780 H20 GPU-hours
+cap      = 500-1175 H20 GPU-hours
+```
+
+因此建议先跑 3-case pilot：
+
+| Pilot case | 起点 | 目的 |
+| --- | --- | --- |
+| topology-only | `TP=4, DP=2, gmu=0.9, mns=64` | 检查不是只会处理 TP8 |
+| runtime-only | `TP=2, DP=1, gmu=0.5, mns=8` | 检查 runtime floor/admission recovery |
+| combined | `TP=1, DP=8, gmu=0.5, mns=16` | 检查 topology + runtime 串联 |
+
+Pilot 通过后再启动完整 20-case suite。