apl: mandelbrot real-axis batched z=z²+c (+9 tests, 296/296)

plans/apl-on-sx.md

@@ -96,7 +96,7 @@ Core mapping:
 ### Phase 6 — classic programs + drive corpus
 - [ ] Classic programs in `lib/apl/tests/programs/`:
   - [x] `life.apl` — Conway's Game of Life as a one-liner using `⊂` `⊖` `⌽` `+/`
-  - [ ] `mandelbrot.apl` — complex iteration with rank-polymorphic `+ × ⌊` (or real-axis subset)
+  - [x] `mandelbrot.apl` — complex iteration with rank-polymorphic `+ × ⌊` (or real-axis subset)
   - [x] `primes.apl` — `(2=+⌿0=A∘.|A)/A←⍳N` sieve
   - [ ] `n-queens.apl` — backtracking via reduce
   - [ ] `quicksort.apl` — the classic Roger Hui one-liner
@@ -118,6 +118,7 @@ data; format for string templating.
 
 _Newest first._
 
+- 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
 - 2026-05-07: Phase 6 primes — sieve via outer-product residue + reduce-first + compress; apl-compress added; lib/apl/tests/programs/primes.apl source; +11 tests; 280/280
 - 2026-05-07: Phase 5 conformance.sh + scoreboard.{json,md} — per-suite runner; current snapshot 269/269; **Phase 5 complete**