plans: tick Phase 3 grade-up/down, progress log

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

plans/apl-on-sx.md

@@ -67,7 +67,7 @@ Core mapping:
 - [x] Take `↑`, drop `↓`, rotate `⌽` (last axis), `⊖` (first axis)
 - [x] Catenate `,` (last axis) and `⍪` (first axis)
 - [x] Index `⌷` (squad), bracket-indexing `A[I]` (sugar for `⌷`)
-- [ ] Grade-up `⍋`, grade-down `⍒`
+- [x] Grade-up `⍋`, grade-down `⍒`
 - [ ] Enclose `⊂`, disclose `⊃`, partition (subset deferred)
 - [ ] Membership `∊`, find `⍳` (dyadic), without `~` (dyadic), unique `∪` (deferred to phase 6)
 - [ ] 40+ tests in `lib/apl/tests/structural.sx`
@@ -118,6 +118,7 @@ data; format for string templating.
 
 _Newest first._
 
+- 2026-05-06: Phase 3 step 5 — grade-up ⍋ / grade-down ⍒ (stable insertion sort); 74/74 tests
 - 2026-05-06: Phase 3 step 4 — squad ⌷ (scalar/multi-dim/partial-slice); 66/66 tests
 - 2026-05-06: Phase 3 step 3 — catenate , (last axis, scalar promo) and first-axis; 59/59 tests
 - 2026-05-06: Phase 3 step 2 — take ↑ (multi-axis, pad), drop ↓, reverse/rotate ⌽⊖ (last+first axis); 50/50 tests