Report latency stats for infeasible baseline

docs/qwen27b-chat-0-8k-tpot40-baseline-infeasible-20260507.md

@@ -19,6 +19,7 @@ Commit: `f212673 Stop tuning when baseline is infeasible`
 Changed behavior:
 
 - `study tune` now persists `tuning_stop_reason` and `tuning_stop_diagnosis` in `state.json`.
+- `study tune` also persists `tuning_stop_details`, including the lowest sampled probe's TTFT/TPOT mean, p50, p95, and p99.
 - After the automatic baseline trial is ingested, AITuner checks the worker result:
   - `status == completed`
   - `best_request_rate is None`
@@ -106,6 +107,15 @@ Baseline probe curve:
 | 0.001953125 | 0.065000 | 0.205128 | false | `slo_pass_rate_unrecoverable` |
 | 0.0009765625 | 0.035000 | 0.142857 | false | `slo_pass_rate_unrecoverable` |
 
+Lowest request rate latency summary:
+
+| Variant | request rate | pass rate | TTFT mean | TTFT p50 | TTFT p95 | TTFT p99 | TPOT mean | TPOT p50 | TPOT p95 | TPOT p99 |
+| --- | ---: | ---: | ---: | ---: | ---: | ---: | ---: | ---: | ---: | ---: |
+| no-harness | 0.035000 | 0.142857 | 1288.953ms | 446.586ms | 3011.814ms | 3011.814ms | 12.661ms | 13.141ms | 15.097ms | 15.097ms |
+| harness | 0.035000 | 0.142857 | 1268.090ms | 445.274ms | 2889.080ms | 2889.080ms | 12.658ms | 13.170ms | 15.102ms | 15.102ms |
+
+This shows that the TPOT threshold of `40ms` is not the binding constraint at the lowest sampled rate. The observed TPOT p99 is about `15.1ms`; failures are driven by TTFT and by the unrecoverable-pass-rate early stop after too many requests have already failed or been skipped.
+
 Final diagnosis written by AITuner:
 
 ```text