Static review delivered 2026-10-30 (Asia/Seoul).
The following is the verbatim reviewer report, not coordinator verification.

I statically reviewed only helpers.py against the contract in requirements.txt, without executing code, editing files, or using the network; the observed model is Opus 5.5 (claude-opus-5-5), as stated in my session environment. Six defects found: (1) page treats number as 0-based, page([1,2,3],1,2) expected [1,2] actual [3], fix start=(number-1)*size; (2) discounted_price subtracts percent as an amount, (200,10) expected 180 actual 190, fix price*(100-percent)/100; (3) cache_key drops tenant, ('a',1) and ('b',1) both give '1' instead of 'a:1'/'b:1', fix f'{tenant}:{record_id}'; (4) p95 uses floor of 0.95n as a 0-based index, which is one rank too high when 0.95n is an integer, p95(list(range(1,21))) expected 19 (rank 19) actual 20, fix ordered[-(-95*len(ordered)//100)-1] (integer ceil avoids float error); (5) word_count splits on single spaces only, 'a  b' expected 2 actual 3, 'a\tb' expected 2 actual 1, '' expected 0 actual 1, fix len(text.split()); (6) mean_or_none([]) raises ZeroDivisionError instead of returning None, fix return None if not values. No defects in stable_unique (dict.fromkeys keeps first occurrence, so [1,True,1.0] gives [1] per Python equality) or clamp (correct when low<=high); the one uncertainty is that the p95 float-rounding claim (0.95*20 evaluates to 19.0) comes from reasoning, not execution, so the p95 counterexample should be confirmed by running it.