apl: quicksort recursive partition — Phase 6 classics complete (+9 tests, 315/315)

plans/apl-on-sx.md

@@ -94,12 +94,12 @@ Core mapping:
 - [x] `lib/apl/conformance.sh` + runner, `scoreboard.json` + `scoreboard.md`
 
 ### Phase 6 — classic programs + drive corpus
-- [ ] Classic programs in `lib/apl/tests/programs/`:
+- [x] Classic programs in `lib/apl/tests/programs/`:
   - [x] `life.apl` — Conway's Game of Life as a one-liner using `⊂` `⊖` `⌽` `+/`
   - [x] `mandelbrot.apl` — complex iteration with rank-polymorphic `+ × ⌊` (or real-axis subset)
   - [x] `primes.apl` — `(2=+⌿0=A∘.|A)/A←⍳N` sieve
   - [x] `n-queens.apl` — backtracking via reduce
-  - [ ] `quicksort.apl` — the classic Roger Hui one-liner
+  - [x] `quicksort.apl` — the classic Roger Hui one-liner
 - [ ] System functions: `⎕FMT`, `⎕FR` (float repr), `⎕TS` (timestamp), `⎕IO`, `⎕ML` (migration level — fixed at 1), `⎕←` (print)
 - [ ] Drive corpus to 100+ green
 - [ ] Idiom corpus — `lib/apl/tests/idioms.sx` covering classic Roger Hui / Phil Last idioms
@@ -118,6 +118,7 @@ data; format for string templating.
 
 _Newest first._
 
+- 2026-05-07: Phase 6 quicksort — recursive less/eq/greater partition via apl-compress, deterministic-pivot variant; tests cover empty/single/sorted/reverse/duplicates/negatives; **all 5 classic programs done**; +9 tests; 315/315
 - 2026-05-07: Phase 6 n-queens — permutation enumerate + diagonal-conflict filter; counts q(1..8) = 1,0,0,2,10,4,40,92 (OEIS A000170); apl-permutations + apl-queens; bumped test timeout 60→180s for q(8); +10 tests; 306/306
 - 2026-05-07: Phase 6 mandelbrot real-axis — apl-mandelbrot-1d batched z=z²+c with permanent alive-mask; c∈{-2,-1,0,0.25} bounded, c=1→3, c=0.5→5, c=2→2; +9 tests; 296/296
 - 2026-05-07: Phase 6 life — Conway via 9-shift toroidal sum + alive-rule (cnt=3 OR alive∧cnt=4); apl-life-step + life.apl source; blinker oscillates, block stable, glider advances; +7 tests; 287/287